Theories of Crime and Justice: Biological Theory

Angela D Crews. 21st Century Criminology: A Reference Handbook. Editor: J Mitchell Miller. Sage Publication. 2009.

Biological theories within the field of criminology attempt to explain behaviors contrary to societal expectations through examination of individual characteristics. These theories are categorized within a paradigm called positivism (also known as determinism), which asserts that behaviors, including law-violating behaviors, are determined by factors largely beyond individual control. Positivist theories contrast with classical theories, which argue that people generally choose their behaviors in rational processes of logical decision making, and with critical theories, which critique lawmaking, social stratification, and the unequal distribution of power and wealth.

Positivist theories are further classified on the basis of the types of external influences they identify as potentially determinative of individual behavior. For example, psychological and psychiatric theories look at an individual’s mental development and functioning; sociological theories evaluate the impact of social structure on individuals (e.g., social disorganization, anomie, subcultural theories, opportunity, strain) and the impact of social function and processes on individuals (e.g., differential association, social learning, social bonds, labeling). Biological theories can be classified into three types: (1) those that attempt to differentiate among individuals on the basis of certain innate (i.e., those with which you are born) outward physical traits or characteristics; (2) those that attempt to trace the source of differences to genetic or hereditary characteristics; and (3) those that attempt to distinguish among individuals on the basis of structural, functional, or chemical differences in the brain or body.

This chapter is organized in rough chronological order and by historical figures associated with an important development. It is difficult to provide an exact chronology, because several important developments and movements happened simultaneously in various parts of the world. For example, although biological theories are considered positivist, the concept of positivism did not evolve until after the evolution of some early biological perspectives. In addition, biological theories of behavior that involve some aspect of evolution, genetics, or heredity are discussed in terms of those scientific developments, although physical trait theories still continued to be popular.

The following sections discuss some of the more important and relevant considerations in scientific developments that impacted biological theories of behavior. A brief history of positivism also is provided, tracing the development and use of the biological theories from early (largely discredited) beliefs, to the most current theories on the relationship of biology to behavior. This section also provides a conclusion that discusses the role of biological theories in the future of criminological thought.

Classical and Positivist Views of Behavior

Biological theories are a subtype of positivist theory. Positivism evolved as instrumental in explaining lawviolating behaviors during the latter part of the 19th century as a response to the perceived harshness of classical school philosophies. Classical thought, which emerged during the Age of Enlightenment (mid-1600s to late 1700s), asserted that man operated on the basis of free will and rational thought, choosing which courses of action to take. According to classical theorists, individuals would engage in behaviors that were pleasurable and avoid behaviors that were painful. Punishment (of the right type and in the right amounts) would deter an individual from committing an act if that punishment resulted in pain that outweighed the pleasure. Classical theorists, for the most part, denounced torture as a type of punishment because it was more punishment than was necessary to prevent a future occurrence of the act; they believed that punishment should be proportionate to the crime to be effective as a deterrent.

Classical views were not very concerned about the causes of behavior. Behaviors were seen as the result of choice rather than as the result of inherent or external factors largely uncontrollable by the individual. The significant progression of scientific thought and method, however, led to the application of science in the study of human and social behavior. The central focus of these new ideas was that the aim of any social action toward individuals who violated law should be curing them, not punishing them.

Positivist criminology is distinguished by three main elements: (1) the search for the causes of crime, whether biological, psychological, or sociological; (2) the use of the scientific method to test theories against observations of the world; and (3) the rejection of punishment as a response to law-violating or deviant behavior, replaced with treatment based on the medical (rehabilitation) model. Positivism rejects free will and replaces it with scientific determinism. Finally, it rejects focus on criminal law and replaces it with a study of the individual.

The Scientific Method

The scientific method is important to positivism and to biological theories of crime because it provides a systematic way to examine a particular problem or issue, rather than relying on spiritual or mystical explanations or haphazard guesswork. The development of the modern scientific method is credited primarily to Ibn al-Haytham (965-1039), an Iraqi-born scientist who wrote The Book of Optics between 1011 and 1021. It consists of the following seven steps:

  1. Observation: Visual examination of a problem or issue, noticing characteristics and patterns.
  2. Statement of the problem: A verbal description of the problem or issue, noting how it impacts and relates to other events or factors. An explanation of why and how the issue or problem is a problem.
  3. Formulation of hypotheses: Development of potential explanations or solutions, educated and informed statements about the expected nature of the problem and relationships among the various components of the problem, specification of variables involved in the problem so that the potential explanation can be tested.
  4. Testing of the hypotheses using controlled experimentation: controlled manipulation of the variables to determine whether the hypotheses are supported.
  5. Analyses of experimental results; this usually involves examination of statistics.
  6. Interpretation of data obtained from the testing and analyses and the formulation of a conclusion: Taking into account all the factors, the researcher makes a conclusion about the nature of the problem or issue.
  7. Publication or dissemination of findings to inform interested populations and future research: providing information to the scientific community about your findings to help future researchers or to inform policy and practice.

Although some variation of the scientific method has been used since ancient times to evaluate and solve many problems, its use to explain social problems, such as crime and criminality, developed more recently. Early types of biological theories of crime were among the first efforts. Given the use of the scientific method in the “hard” or “natural” sciences, early researchers of the causes of crime attempted to explain criminal behaviors by applying the scientific method. The most obvious place to look for differences between criminals and other individuals was on the outside, by studying physical traits.

Physical Trait Theories

The belief that one can determine a person’s character, moral disposition, or behavior by observing his or her physical characteristics is ancient. Pythagoras, a philosopher, mathematician, and scientist who lived during the period around 500 BCE, may have been one of the first to advocate this practice, known as physiognomy.


The term physiognomy comes from the Greek words physis, meaning “nature,” and gnomon, meaning “to judge or to interpret.” It refers to the evaluation of a person’s personality or character (i.e., his or her nature) through an examination of that person’s outward appearance. Early physiognomy concentrated on characteristics of the face through which to judge the person’s nature. Aristotle, a Greek philosopher who lived from 384 to 322 BCE, was a proponent of physiognomy, as were many other ancient Greeks. The practice flourished in many areas of the world and was taught in universities throughout England until it was banned by Henry VIII in 1531.

Giambattista della Porta (1535-1615)

The publication of On Physiognomy in 1586 by Italian scholar Giambattista della Porta once again brought renewed focus to this belief and practice of the ancient Greeks. Della Porta, often considered the first criminologist, examined patients during his medical practice and concluded that appearance and character were related. He approached the study of this relationship from a magico—spiritualistic metaphysical perspective instead of a scientific one, classifying humans on the basis of their resemblance to animals. For example, men who look like donkeys are similar to donkeys in their laziness and stupidity; men who resemble pigs behave like pigs.

Johann Kaspar Lavater (1741-1801)

Della Porta’s ideas were extremely influential to Johann Kaspar Lavater, a Swiss pastor who published his painstakingly detailed study of facial fragments in 1783. He concluded that one could determine criminal behavior through an examination of a person’s eyes, ears, nose, chin, and facial shape.


Phrenology, from the Greek words phren, meaning “mind,” and logos, meaning “knowledge,” is based on the belief that human behavior originated in the brain. This was a major departure from earlier beliefs that focused on the four humors as the source of emotions and behaviors: (1) sanguine (blood), seated in the liver and associated with courage and love; (2) choleric (yellow bile), seated in the gall bladder and associated with anger and bad temper; (3) melancholic (black bile), seated in the spleen and associated with depression, sadness, and irritability; and (4) phlegmatic (phlegm), seated in the brain and lungs and associated with calmness and lack of excitability. Theoretically and practically relocating responsibility for behavior from various organs to the brain represented a major step in the development of the scientific study of behavior and in the development of biological explanations of crime and criminality.

Franz Joseph Gall (1758-1828)

Around 1800, Franz Joseph Gall, a German neuroanatomist and physiologist who pioneered study of the human brain as the source of mental faculties, developed the practice of cranioscopy, a technique by which to infer behaviors and characteristics from external examination of the skull (cranium). According to Gall, a person’s strengths, weaknesses, morals, proclivities, character, and personality could be determined by physical characteristics of his or her skull.

Gall mapped out the location of 27 “brain organs” on the human skull. A bump or depression in a particular area of the skull would indicate a strength or weakness in that particular area. For example, several areas of Gall’s map of the skull were believed to correspond to that person’s tendencies to engage in criminal or deviant acts. One area corresponded to the tendency to commit murder; another area corresponded to the tendency to steal. Although not widely accepted in Europe, the English elite (and others) used Gall’s ideas to justify the oppression of individuals whose skulls had bumps or depressions in the wrong areas. The practice also was widely accepted in America between 1820 and 1850. Although crude, and somewhat ridiculous by today’s standards, Gall’s efforts had significant impact on subsequent research that attempted to identify the brain as the origin of behavior. Although similar to physiognomy in that it tried to make inferences about character and behavior from outward characteristics, cranioscopy attempted to correlate those outward physical characteristics to internal physical characteristics (i.e., brain shape), which was a significant advance.

Johann Spurzheim (1776-1832)

Spurzheim, a German physician and student of Gall’s, actually coined the term phrenology to replace cranioscopy. Spurzheim also expanded the map of the brain organs, developed a hierarchical system of the organs, and created a model “phrenology bust” that depicted the location of the brain organs.

While the German scientists were focusing attention on the brain as an important determinant of individual behavior, various other scholars were theorizing about the development of man as a biological organism; about the nature of social and political organizations; and about the place of man, as an individual, within those organizations. The synthesis of these ideas would significantly advance the progress of research related to biological perspectives of behavior.

The Origins of Humanity and the Mechanisms of Inheritance

Since the beginning of time, humans have questioned their origins. Earliest explanations focused on mystical/magical and spiritual forces, often centered on creationism, the theory that life originated from a divine source. The power of the organized religions in shaping man’s social, political, economic, and legal systems is testament to their immense influence. For example, religious perspectives dominated philosophical thought until the Scientific Revolution began in the mid-16th century, when advances in theory and practice provided explanations alternative to those promulgated by the church. Galileo Galilei (1564-1642), Johannes Kepler (1571-1630), René Descartes (1596-1650), and Isaac Newton (1643-1727) all made significant contributions that brought scientific reasoning to the forefront of thought as a competitor to spiritual explanations. Although usurping the philosophies of the church were not their main goals, their revolutionary ideas (that natural events and human behaviors may be explained by the development and application of certain scientific principles) had just that effect. Needless to say, secular science was not very popular with the church and organized religion. However, these changes were vital in advancing understanding of human and societal behavior.

Persistence of Human Traits and Characteristics

In addition to having been the potential source of physiognomy, ancient Greek philosophers also were among the first to recognize and attempt to explain the persistence of traits and characteristics from one generation to the next. Plato and Aristotle used the concept of association to explain how current mental processes (especially memories) generate from prior mental processes. These beliefs broadened to include all mental processes in the hands of philosophers such as Hume, Mill, and Locke.

Given that memories and other, possibly undesirable, characteristics and traits could potentially persist through generations, Plato advocated the control of reproduction by the state (government). Infanticide was practiced as a form of population control in ancient Rome, Athens, and Sparta. Many of the ancient societies also engaged in practices to weed out weak, diseased, malformed, or otherwise unfit members, such as exposing young children to the elements to see which ones had the strength, intelligence, and wit to survive.

Scientists began studying the nature of persistent traits in plants and animals prior to the application of these ideals to humans. Once established, however, it took relatively little time and relatively little effort to explain human patterns with these principles. As readers will note, the mid-to late 18th century was characterized by rapid progress in the natural sciences, which positively impacted biologically oriented research in the social sciences.

Carolus (Carl) Linnaeus (1707-1778)

Linnaeus, a Swedish botanist, zoologist, and physician, was among the first to document traits, patterns, and characteristics among plants and animals, creating hierarchical taxonomies (systems of classification). In Systema Naturae (System of Nature), published in 1735, Linnaeus grouped humans with other primates, becoming one of the first to recognize similar characteristics across species, hinting at an evolutionary progression.

Pierre-Louis Moreau de Maupertuis (1698-1759)

In 1745, French philosopher and mathematician Maupertuis published Venus Physique (Physical Venus), in which he proposed a theory of reproduction in which organic materials contained mechanisms to naturally organize. He subsequently discussed his views on heredity and examined the contributions of both sexes to reproduction, examining variations through statistics. Whether Maupertuis can be credited with being among the first to attempt to elucidate a theory of evolution is actively debated. He is generally credited with outlining the basic principles of evolutionary thought, along with his contemporary, James Burnett (see James Burnett, Lord Monboddo [1714-1799] section).

David Hartley (1705-1757) and the Associationist School

Hartley (borrowing somewhat from philosopher John Locke) published his most influential work—Observations on Man, His Frame, His Duty, and His Expectations—in 1749. In it, he attempted to explain memory and thought, in general, through the doctrine of association. This was significant, because he attempted to link the processes of the body to the processes of the brain. He explained that actions and thoughts that do not result immediately from an external stimulus are influenced by the constant activity of the brain because of man’s past experiences, mediated by the current circumstances, causing man to act in one way or another. This brain activities that Hartley called sensations are often associated together and become associated with other ideas and sensations, forming new ideas. Hartley’s work was important in that it brought scientific focus to the process of thought, the origin of emotions, and the impact of feelings on the creation of voluntary action. This is a positivist philosophy in that action is not viewed as being the direct result of strict free will.

George-Louis Leclerc, Comte de Buffon (1707-1788)

From 1749 to 1778, Leclerc published his most famous and influential work in 36 volumes, with an additional 8 volumes published postmortem. It was a study of natural history, from the general to the specific. In this work, he proposed the idea that species, including humans, change (i.e., evolve) throughout generations. Following in the footsteps of Linnaeus, he also proposed the radical idea of a relationship between humans and apes.

In another controversial publication, The Eras of Nature (1778), Leclerc questioned the long-standing and sacred belief that the universe was created by a divine power, instead suggesting that our solar system was created by celestial collisions. Finally, he contradicted the notion that seemingly useless body parts on animals were spontaneously generated but instead were vestigial, remnants of evolutionary progress.

Leclerc’s influence was widespread and impacted subsequent beliefs about the transmission of traits from one generation to the next (inheritance, heredity) as well as about changes that occur over time with each passing generation (evolution). These ideas significantly impacted biological theories of behavior. Charles Darwin, in fact, credited Leclerc with being the first modern author of the time to treat evolution as a scientific principle.

James Burnett, Lord Monboddo (1714-1799)

Burnett, a Scottish judge, is credited with being another of the first to promote evolutionary ideas, in particular, the idea of natural selection. In The Origin and Progress of Language (1773), Burnett analyzed the development of language as an evolutionary process; he clearly was familiar with the ideas of natural selection, although he differed with Leclerc in his support of the notion that humans were related to apes.

Erasmus Darwin (1731-1802)

One individual who took Leclerc’s ideas to heart was Erasmus Darwin, grandfather of Charles Darwin and Francis Galton (see subsequent sections on Charles Darwin and Galton). Darwin also integrated ideas from Linnaeus, translating Linnaeus’s works from Latin to English and publishing his own book of poetry about plants, The Botanic Garden (1791). Between 1794 and 1796, Darwin publishedZöonomia, which discussed the concept of generation (reproduction) and used Hartley’s theory of association (and possibly Linneaus’s taxonomies). Many scholars believe Darwin’s propositions were the forerunners of a more well-defined theory of inheritance later argued by Jean-Baptiste Lamarck (see Jean-Baptiste Lamarck [1744-1829] section).

Thomas Robert Malthus (1766-1834)

In 1798, Malthus, an English demographer and political economist, published An Essay on the Principle of Population, in which he proposed that populations struggle for existence in competition over resources. His main premise was that increases in population result in increased competition for scarce resources, primarily food. As a society becomes overpopulated, those at the bottom of the socioeconomic strata suffer the most (and often die). He explained that some natural events and conditions serve to control population growth (e.g., war, disease, famine) and that moral restraint (e.g., abstinence, late marriage) could serve the same function.

Contrary to many economists of the time who believed that increasing fertility rates and populations would provide more workers and would increase the productivity of a society, Malthus argued that the provision of resources could often not keep pace with population growth and would result in more poverty among the lower classes. This depiction of a struggle for existence was applied by subsequent scientists to plants and animals and was instrumental to Charles Darwin (and others) in arguments about “natural selection” and “survival of the fittest” (a phrase coined by Herbert Spencer; see Herbert Spencer [1820-1903] section).

Jean-Baptiste Lamarck (1744-1829)

Lamarck was a French naturalist, mentored by Leclerc (see preceding section on Leclerc), who published Recherches sur l’Organisation des Corps Vivans (Research on the Organization of Living Things) in 1802. Lemarck was among the first to attempt to classify invertebrates and was among the first to use the term biology. He primarily is known for promoting and advocating a theory of soft inheritance, orinheritance of acquired characters, in which characteristics developed during the lifetime of an organism (e.g., larger or stronger muscles) are passed along to subsequent generations, making them better suited for survival (or better adapted).

Lemarck is considered the first to articulate a coherent theory of evolution, although he believed that organisms came into being through spontaneous generation instead of sharing a common source. His theory was characterized by two main arguments: (1) that organisms progress from simpler to more complex through generations and (2) that organisms develop adaptations because of their environments or because of the necessity (or lack thereof) of particular characteristics (the use-it-or-lose-it aspect).

The Impact of Positivism

In the early 1800s, following the advancement of arguments, proposals, and theories related to the biological sciences, and during the discussions of Malthus’s revolutionary “struggle for existence,” groundbreaking ideas also were being propagated about the place and function of man within social groups. These developments were instrumental to the application of biological perspectives to human behavior within social groups.

Auguste Comte (1798-1857)

Known as the “Father of Sociology,” Comte was a French scholar who published Plan de Travaux Scientifiques Nécessaries Pour Réorganizer la Société (Plan of Scientific Studies Necessary for the Reorganization of Society) in 1822. In this work, he argued for a universal law of three phases: (1) theological, (2) metaphysical, and (3) scientific, through which all societies have, or will, progress.

The theological stage is the most primitive stage, characterized by supernatural, religious, or animistic explanations for events, situations, and behaviors and a lack of interest in the origins of causes. The metaphysical stage is slightly more advanced and identifies abstract forces (fate, accident) as the origin of causes. The most advanced stage, the scientific stage, is what Comte called the positive stage. At this point, there is little concern for the origin of actions, but a focus on the outcomes, which man can control.

Positive stages are characterized by observation, experimentation, and logic and attempt to understand the relationships among components. Comte’s positivism attempted to apply scientific principles (i.e., the scientific method) to the behavior of societies and to the behavior of groups within societies and emphasized the connectedness of all the elements involved in behavior. Positivism is one of the first theories of social evolution, attempting to explain how societies progress. Comte claimed that the only real knowledge is knowledge gained through actual sense experience (i.e., observation).

Comte’s scientific stage also is exemplified by the use of quantitative, statistical procedures to make logical, rational decisions based on evidence. Statistical procedures had been used for some time in the hard sciences (e.g., math, physics), but a positivist perspective required that the use of such measurement techniques be applied to the social sciences, as well.

Statistics and the Social Sciences

Adolphe Quetelet (1796-1894) and Andre-Michel Guerry (1802-1866)

Despite the overwhelming complexity of social phenomena, Quetelet and Guerry were convinced that it was possible to apply statistical techniques to the investigation of social behavior. Both men were primarily interested in unraveling the statistical laws underlying social problems such as crime and suicide. This idea was controversial at the time, because it contradicted prevailing belief in free will. Quetelet’s most influential publication was Sur L’Homme et le Développement de ses Facultés, ou Essai de Physique Sociale (Treatise on Man; 1835), in which he described the “average” man, developed from the calculation of mean values to form a normal distribution. Quetelet called this process social physics, a term that Comte had earlier used. Quetelet’s appropriation of the phrase social physics prompted Comte to adopt the term sociology instead.

Guerry is known for developing the idea of moral statistics in an 1829 one-page document containing three maps of France, shaded in terms of crimes against property, crimes against persons, and a proxy for education (school instruction). A subsequent publication, Essay on Moral Statistics of France (1833), expanded on this technique and developed shaded maps to evaluate crime and suicides by age, sex, region, and season. He found that these rates varied by region but remained remarkably stable across the other factors.

This preliminary work emphasized the possibility that social measurements could provide insight into the regularity of human actions, forming a basis for the development of social laws, similar to the physical laws that govern the behavior of other objects and events in nature. Quetelet and Guerry were instrumental in the development of sociology and criminology, illustrating the possibility of measuring, determining the nature of relationships, and identifying patterns and regularities in social situations.

Heredity and Evolution

As the search for explanations of individual and social behavior improved through the application of statistical methods and the positivist insistence that the only real knowledge was that obtained through systematic observation (i.e., the scientific method), beliefs about the nature and potential of man within society became more sophisticated and grounded. Although Lemarck had earlier discussed the passage of certain acquired traits from generation to generation (soft inheritance), theorists in the mid-1800s benefited from Malthus’s propositions about the progress of society and from increasingly sophisticated inquiries into the nature and source of biological and behavioral predispositions.

Herbert Spencer (1820-1903)

An early English social theorist and philosopher, Spencer articulated a theory of evolution in Progress: Its Law and Cause (1857), prior to the publication of Charles Darwin’s On the Origin of Species in 1859. Spencer proposed that everything in the universe developed from a single source and progressed in complexity with the passing of time and generations, becoming differentiated yet being characterized by increasing integration of the differentiated parts. Spencer also coined the phrase survival of the fittest, in 1864, after reading Darwin’s On the Origin of Species, and he applied the idea of natural selection to society.

Charles Darwin (1809-1882)

Although the preceding paragraphs illustrate the development of scientific thought on the concepts of heredity and evolution, most scholars primarily note the impact of Charles Darwin. Darwin described his theories in two main publications: (1) On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life (1859) and (2) The Descent of Man and Selection in Relation to Sex (1871).

In On the Origin of Species, Darwin detailed the theory that organisms evolve over generations through a process of natural selection. Darwin reached his conclusions and supported his observations through evidence that he collected during a sea voyage on a boat, the HMS Beagle, during the 1830s.

The Descent of Man and Selection in Relation to Sex applied Darwin’s theory to human evolution and described the theory of sexual selection. Although he had earlier hinted that natural selection and evolution could and should be applied to the development of man, others (Thomas Huxley in 1863, Alfred Wallace in 1864) had actually applied his theories to the human animal first.

Cesare Lombroso (1835-1909)

Among the first to apply Darwin’s findings to criminal behavior and criminals, Lombroso was an Italian criminologist and founder of the Italian School of positivist criminology. Lombroso rejected the established Classical School, which held that crime was a characteristic trait of human nature. Instead, using concepts drawn from earlier perspectives, such as physiognomy, Lombroso argued, in essence, that criminality was inherited and that someone “born criminal” (this phrase was coined by his student, Enrico Ferri) could be identified by physical defects, which confirmed a criminal as savage, or atavistic.

Lombroso published Criminal Man in 1876, helping to establish the newly forming Positive School of criminology. Inspired by Charles Darwin’s evolutionary theory, he believed that criminals were not as evolved as people who did not commit crime and that crime is a result of biological differences between criminals and noncriminals.

A central focus of Lombroso’s work is the concept of atavism. Atavism describes the reappearance in an organism of characteristics of some remote ancestor after several generations of absence. It often refers to one that exhibits atavism, that is, a throwback. It can also mean a reversion to an earlier behavior, outlook, or approach. Lombroso approached this concept believing that criminals were throwbacks on the evolutionary scale. He believed that modern criminals shared physical characteristics (stigmata) with primitive humans. In his later years, he eventually thought that social and environmental factors can contribute to criminality.

Lombroso reached his conclusions by studying the cadavers of executed criminals for physical indicators of atavism, developing a typological system (with four main criminal types) to categorize these individuals. Although his methods were flawed, and most of the traits he listed failed to distinguish criminals from matched samples of noncriminals, he was among the first to apply scientific principles to the collection of data and to use statistical techniques in his data analysis. In addition to examining the physical characteristics of the criminal, he also evaluated the conditions under which crime is committed. He also was among the first to study female criminality, speculating that females were more likely to be criminals “by passion.”

Lombroso determined that serious offenders inherited their criminal traits and were “born criminals,” atavistic throwbacks to earlier evolutionary ancestors. They had strong jaws, big teeth, bulging foreheads, and long arms. These types of offenders constituted about one third of all criminals. The remaining two thirds were “criminaloids” (minor offenders) who only occasionally commit crime.

Although primarily remembered for his claim that criminal behaviors were inherited, Lombroso also argued that environmental factors can play an important role in crime. He speculated that alcoholism, climate changes, and lack of education may contribute to criminality.

Lombroso’s work started other researchers on the path to determine a hereditary source for criminal behavior. His student, Enrico Ferri (1856-1929), disagreed with Lombroso’s focus on the physiological, preferring instead to examine the interactive effects of physical factors, individual factors, and social factors and to blame criminality on a lack of moral sensibility.

Another Italian contemporary, Raffaele Garofalo (1851-1934), developed a theory of natural crime, focusing on those acts that could be prevented or reduced by punishment. Garofalo also suggested the elimination of individuals who posed a threat to society, to improve the quality of the society and ensure its survival. Like Ferri, he believed crime was more the result of a lack in moral sensibilities rather than a physiological problem.

Lombroso’s conclusions were challenged and refuted by Charles Goring (1870-1919), who wrote The English Convict in 1913. In a carefully controlled statistical comparison of more than 3,000 criminals and noncriminals, Goring found no significant physical differences between the two populations except height and weight (criminals were slightly smaller). His findings essentially discredited Lombroso’s idea of the born criminal, although research into the search for criminal types continued.

The Criminal Physique

Evaluations and categorizations of a person’s body build or physique also became popular as researchers attempted to link crime with some outwardly observable differences. In 1925, Ernst Kretschmer (1888-1964), a German psychiatrist, published Physique and Character, in which he described three categories of body type (asthenic, athletic, pyknik) associated with three categories of behaviors (cyclothemic, schizothemic, and displastic). Cyclothemes were manic-depressive and typified by soft skin, a round shape, and little muscle development, and tended to commit the less serious offenses that were more intellectual in nature. Schizothemes were antisocial and apathetic, committing the more serious violent offenses, and were either asthenic (thin and tall) or athletic (wide and strong). Displastics could be any body type but were characterized by highly charged emotional states and unable to control their emotions. Kretschmer associated displastics with sexual offenses. Although Kretschmer attempted to develop a typology that associated behaviors with physique, he did not put much consideration into the complex nature of behavior and its interaction with the environment.

Among those who continued this search was a contemporary of Goring, Harvard anthropologist Ernest Hooten (1887-1954). Dissatisfied with Goring’s findings, Hooten spent 12 years conducting research into the criminal nature of man to disprove Goring and to support Lombroso. His first influential publication, Crime and the Man (1939), documented his study of 14,000 prisoners and 3,000 nonprisoner controls in 10 states. Hooten was more rigorous than Goring in his methods, differentiating his subjects on the basis of types of crime and by geographic, ethnic, and racial backgrounds.

Hooten agreed with Lombroso’s idea of a born criminal and argued that most crime was committed by individuals who were “biologically inferior,” “organically inadaptable,” “mentally and physically stunted and warped,” and “sociologically debased.” He argued that the only way to solve crime was by eliminating people who were morally, mentally, or physically “unfit,” or by segregating them in an environment apart from the rest of society.

As Hooten was conducting his research and developing his conclusions, the sociological world was developing an interest in the contribution of social factors and social environments to the development of criminal behavior. Sociological research out of the University of Chicago (i.e., the Chicago School) stressed the impact of the social environment rather than an individual’s biology as crucial to the development of crime. Hooten was widely criticized because of his failure to consider social factors and his myopic focus on biological determinism.

Gregor Mendel (1822-1884)

While scholars debated Darwin’s claims and investigated whether criminals were born and were atavistic throwbacks to earlier historical periods, a piece of research on heredity in plants that was largely overlooked at the time it was published in 1866 was being rediscovered. This work provided quantitative evidence that traits were passed on from one generation to the next (or inherited), making it one of the most critical pieces of research related to biological theories of crime.

Mendel, an Austrian scientist, is known as the “father of genetics” (Henig, 2000). Although Mendel’s work was largely ignored until after 1900 (in part because of the popularity of Darwin’s theories), application of his laws of inheritance to individual and social development resulted in significant advances in biological theories of behavior.

Mendel’s experiments with plants (in particular, peas) and with animals (in particular, bees) provided scientific support to some of the propositions suggested by Darwin in 1868, although Mendel’s research predates that of Darwin. Darwin theorized that pangenesis explained the persistence of traits from one generation to the next. He discussed transmission and development in his laws of inheritance, arguing that cells within bodies shed “gemmules” that carried specific traits from the parent organism to the subsequent generation. Darwin insightfully proposed that a parent organism’s gemmules could transmit traits to the following generation even though those traits may not have been present in the parent and that those traits could develop at any later point.

Mendel, however, was the one who developed support for the theory of inheritance through his experiments with the cultivation and breeding of pea plants, and the scientific support for dominant andrecessive characteristics, passed from one generation to the next. His work also led to focus on the study of traits at the cellular level (geno-types) instead of at the observable level (phenotypes).

The Implications of Heredity and Evolution: Eugenics and Social Darwinism

Francis Galton (1822-1911) and Eugenics

It was in the work of Galton, a cousin of Charles Darwin, that statistics, biology, and sociology reached a harmonic state. Reading Darwin’s theories about variations in the traits of domestic animals set Galton on a path to study variations in humans. In doing so, he developed measurement techniques and analytic techniques to help him make sense of what he was observing. He first was interested in whether human ability was hereditary, and he collected biographical information about numerous prominent men of the time to chart the families’ abilities over several generations. He published his results in a book called Hereditary Genius (1869), in which he concluded that human ability was inherited. He followed this work with a survey of English scientists (1883) in which he attempted to determine whether their interest and abilities in science were the result of heredity (nature) or encouragement (nurture). Galton stimulated interest in the question of (and coined the phrase) nature versus nurture.

Although Galton’s work at that point was useful and had resulted in the development of numerous measurement tools (e.g., the questionnaire; fingerprint analysis) and statistical concepts (standard deviation, correlation, regression), it was his work with twins that provided the impetus for future inquiries into the nature-versus-nurture debate. Galton surveyed sets of twins to determine whether twins who were identical exhibited differences if raised in different environments and whether twins who were fraternal exhibited similarities if raised in similar environments. This work was published as “The History of Twins as a Criterion of the Relative Powers of Nature and Nurture” in 1875.

In 1883, Galton developed the concept of eugenics, his most controversial and abused philosophy. Eugenics advocated the encouragement, through the distribution of incentives, of “able” couples to reproduce in an effort to improve human hereditary traits. Part of his proposals included manipulating social morals to encourage the reproduction of the “more fit” and discourage reproduction of the “less fit.” Galton’s proposals were to change social mores and values rather than forcibly manipulating reproduction or eliminating those who were considered less fit. He believed that, without encouragement, it was the natural state of man (and thus of society) to revert to mediocrity, a phrase that came to be clarified as “regression toward the mean,” which he viewed as repressive of social and individual progress.

Prevailing thought at the time was receptive to such ideals, in the belief that these policies would reduce or eliminate poverty, disease, genetic deformities, illnesses, and crime. Eugenics was originally conceived as a concept of social responsibility to improve the lives of everyone in society by encouraging individuals to selectively breed good traits in and bad traits out, but many who followed would use Galton’s philosophies toward less than desirable ends.

After Galton’s efforts, others attempted to document that crime was a family trait. In 1877, Richard Dugdale (1841-1883) published The Jukes: A Study in Crime, Pauperism, Disease and Heredity, in which he traced the descendants of matriarch Ada Jukes and found that most of the Jukes family members (although they were not all biologically related) were criminals, prostitutes, or welfare recipients. Another family study, published in 1912 by Henry H. Goddard (1866-1957), traced 1,000 descendants of a man named Martin Kallikak, comparing his descendants who were conceived within wedlock to a woman of “noble birth” to his descendants who came from the bloodline he conceived out of wedlock with another woman, one of ill repute. Goddard concluded (although he later retracted his conclusions) that the legitimate bloodline was “whole-some,” whereas the illegitimate bloodline was characterized by “feeblemindedness.”

Social Darwinism

Developments that ensued after Galton’s propositions of eugenics, and after the rediscovery and replication of Mendel’s work on the heritability of traits, were crucial to the study of man’s behavior, its potential biological roots, and to the study of man’s role and obligation in society. Malthus’s struggle for existence, Comte’s sociology, Quetelet and Guerry’s social physics and moral statistics, and the work of scientists (most notably Darwin) on transmutation, natural selection, survival of the fittest, and evolution resulted in perfect conditions under which scientific principles and statistical analysis could be applied to the human condition and to human behavior. A compilation of these philosophies resulted in the theory of social Darwinism, originally applied to the structure and function of social processes and organizations (e.g., government), with the primary belief that competition drives all social progress and only the strongest survive.

Mendel’s contribution was critical to the ideas of social Darwinism, explaining how observable characteristics (phenotypes) were inheritable and how a trait may appear in one generation that had not appeared in many prior generations. These atavisms, or throwbacks to an earlier evolutionary period, could be physical (e.g., vestigial tails, useless appendages) or behavioral (e.g., violence). Social Darwinists became interested in the question of whether social development (progress, evolution) could be engineered or controlled through manipulation of these traits. Other scientists studying the more undesirable behaviors of man (e.g., crime) were interested in whether social problems could be controlled through this type of manipulation. Many, however, such as noted political economist William Graham Sumner (1840-1910), advocated a laissez-faire philosophy with respect to the survival and progress of societies, noting that problems like poverty are the natural result of inherent inequalities and that the process of natural selection and survival of the fittest would mean a natural reduction in the problems over time (without social engineering or interference; Hodgson, 2004). Viewing society through the lens of social Darwinism, however, inevitably led to viewing man through the lens of social Darwinism.

During the late 1800s and early 1900s, while Goring, Hooten, and others were debating the role of biology in criminal behavior, others were quietly merging Malthus’s ideas on competition and survival among societies, Spencer’s insistence that individual evolution leads to social evolution, Mendel’s ideas on the heritability of traits, Darwin’s ideas on natural selection and evolution, and Galton’s ideas on eugenics into warped interpretations and applications of eugenics and social Darwinism.

The Legacy of Eugenics and Social Darwinism

With unprecedented immigration in the late 19th and early 20th centuries, American society struggled with increasing crime, poverty, suicide, and other social problems. Some, such as the theorists of the Chicago School, saw the solution in sociological explanations, whereas others turned to solutions implied in eugenics. Although a complete description of the misapplication of eugenics is beyond the scope of this chapter, it is important for the student of biological theories to understand the impact that eugenics had on the study of biological explanations of behavior.

In theory, eugenics argued for the improvement of human genetic qualities. Positive eugenics aims to increase the reproduction of desirable qualities, and negative eugenics aims to discourage the reproduction of undesirable qualities, to improve humanity and society. The underlying premise is that both positive and negative traits are inherited and passed down through generations. Early eugenicists focused on traits such as intelligence and on hereditary diseases or defects presumed to be genetic (Barrett & Kurzman, 2004). These eugenicists, following Galton’s philosophies, focused on societal changes (the provision of incentives) to encourage reproduction among those with positive traits and to discourage reproduction among those with negative traits.

In practice, however, and following a logical progression of thought, some believed eugenics to mean that persons with undesirable traits should be prevented from reproducing, or even be eliminated.

Although social Darwinists and eugenicists are alike in their goal to improve humanity and society through survival of the fittest, social Darwinists were more likely to assert that this improvement would take place in a natural process, with weak, diseased, undesirable, and unfit individuals being eventually weeded out. It is for this reason that social Darwinists opposed government intervention into problems such as poverty and crime, believing that natural forces would result in the reduction of elimination of these undesirable conditions. Eugenicists, on the other hand, encouraged active intervention.

It is this active intervention that became problematic, although it was not initially viewed as such. Activists promoted the use of contraception to prevent unwanted pregnancies, and state laws were written regulating marriages. Individuals who had ailments thought to be genetic were prohibited from marrying and forcibly sterilized. This included individuals deemed to be “feeble-minded” or mentally ill.

The popularity of eugenics spread throughout the United States during the late 1800s and early 1900s. Charles Davenport (1866-1944), an influential American biologist, directed the Cold Spring Harbor Laboratory in 1910 and founded the Eugenics Record Office, hiring Harry H. Laughlin (1880-1943) as superintendent (Kevles, 1985).

Between 1907 and 1914, several states had passed sterilization laws. Laughlin, however, perceived these as ineffective and full of holes, prompting him in 1922 to draft a “model” law that was passed by 18 additional states (Lombardo, n.d.). In this model law Laughlin defined the populations that would be targeted by forced sterilization, including criminals, the very poor, epileptics, alcoholics, the blind, the deaf, the insane, and those who had a physical deformity. These practices were upheld as constitutional by the U.S. Supreme Court in 1927 in the case of Buck v. Bell and continued until 1981. More than 64,000 individuals in 33 states were forcibly sterilized under these laws.

With increased immigration came increased concerns about the quality and purity of the races. Responding to these concerns, Madison Grant (1865-1937), an American lawyer, wrote one of the first and most influential books about racial integrity, The Passing of the Great Race (1916). Grant wrote that the Nordic (i.e., white) racial line was the pinnacle of civilization. He warned against miscegenation (race mixing) and supported legislation against it. He argued for racial hygiene because the Nordic race was superior to any other, and any mixing would taint Nordic bloodlines, making them impure. He also warned that “undesirables” breed in greater numbers and would over-run the superior Nordic population if not controlled. He advocated the eradication of “undesirables” from the human gene pool coupled with the promulgation of more desirable and worthy racial types.

Grant’s work was immensely popular and was instrumental in the drafting and passage of the Immigration Act of 1924, which restricted the numbers of immigrants from the less desirable regions, such as southern and eastern Europe. His book also was translated into several languages. In 1925, it was translated into German, in which Nordic was replaced by the word Aryan. Adolph Hitler, who read the book shortly after its translation into German, would later call Grant’s work his “bible.”

In 1928, with sterilization laws and immigration restrictions in full swing, E. S. Gosney (1855-1942) founded the Human Betterment Foundation, an entity whose primary purpose was to compile and distribute propaganda about compulsory sterilization. Gosney hired Paul E. Popenoe (1888-1979) to assist him in the study of the impact of these sterilization laws in California. Their collaboration resulted in the publication of Sterilization for Human Betterment: A Summary of Results of 6,000 Operations in California, 1909-1929 (Gosney & Popenoe, 1929), used by Nazi Germany to support its 1934 Law for the Prevention of Hereditarily Diseased Offspring. Furthermore, these arguments were used to justify policies of racial hygiene and racial cleaning that Nazi Germany enacted against Jews and other “undesirable” or “unfit” persons who did not meet the model of the Aryan ideal. The Nuremburg Laws enacted in 1935 consisted of the Law for the Protection of German Blood and German Honor, and the Reich Citizenship Laws, which prohibited the mixing of Germans with Jews (which really meant anyone not deemed to be German) and stripped so-called undesirables of their citizenship.

Although population control policies based on eugenics enjoyed widespread support in many countries prior to World War II, Nazi use of its philosophies to justify the eradication of approximately 6 million Jews and an additional 3 to 5 million others brought an immediate halt to its proliferation. However, sterilizations, marriage restrictions based on fitness, and prohibitions of racial intermarriage continued for decades. Marriage counseling, ironically developed by Paul Popenoe as a eugenic tactic to ensure marriage between fit individuals, also became a viable area of practice.

Despite the fact that the word eugenics is usually avoided, modern efforts to improve humanity’s gene pool persist. The Human Genome Project is one notable scientific effort to understand the genetic makeup and properties of human beings with an eye toward eradicating or preventing inheritable diseases and defects. Advances in science and the development of ethical guidelines provide hope that struggles to better understand the transmission and development of human traits and characteristics are not yet abandoned. This is especially important to the future of biological theories of criminality.

Post-World War II Research on Biology and Behavior

Body Physique and Crime

After World War II, research into the biological roots of crime persisted. Following in the footsteps of Lombroso in 1876, Kretschmer in 1925, and Hooten in 1939, William H. Sheldon (1898-1977) attempted to document a direct link between biology (specifically, physique) and personality (specifically, crime) through the development of a classification system of personality patterns and corresponding physical builds (Sheldon, 1940).

Running contrary to prevailing sociological emphases on the environmental correlates of crime, Sheldon chose to instead employ beliefs about Darwin’s survival of the fittest, Lombroso’s criminal man, and Galton’s eugenics. Sheldon argued for an “ideal” type, in which perfectly formed physique joined perfectly formed temperament and disposition. Any combination that deviated from this ideal was associated with disorders of both personality and behavior. He claimed a physical basis for all variations in personality and body build.

During the 1940s, Sheldon developed and tested his classification system, known as somatotyping. He created three classifications: (1) ectomorphs, who were thin, delicate, flat, and linear; (2) endomorphs, who were heavy or obese, with a round, soft shape; and (3) mesomorphs, who were rectangular, muscular, and sturdy.

In subsequent studies of juvenile delinquency, Sheldon argued that mesomorphic types were more likely to engage in crime, ectomorphs were more likely to commit suicide, and endomorphs were more likely to be mentally ill. Although Sheldon linked physical and psychological characteristics and concluded that both were the result of heredity, he failed to support that conclusion with valid statistical methods.

Also during the late 1940s and early 1950s, Sheldon Glueck and Eleanor Glueck conducted longitudinal research into juvenile delinquency using control groups and added to Sheldon’s list of somatotypes. They suggested the addition of a fourth type they called balanced. In their research, they found support for Sheldon’s proposition that mesomorphs are more likely to commit crime. Among the juveniles they studied, the mesomorphic somatotype was disproportionately represented among delinquents by a ratio of nearly two to one as compared with nondelinquent controls. In addition, whereas only about 14% of delinquents could be classified as ectomorphs, nearly 40% of the nondelinquent controls could be placed in this category. Instead of concluding that body type led to delinquency, the Gluecks (1956) concluded that participation in delinquency (for which individuals are more likely to get arrested) may be facilitated by having a mesomorphic body type rather than an ectomorphic, endomorphic, or balanced body type.

Biological explanations for behavior lost much of their popularity during the 1960s with the belief that their inherent implication of inferiority often was misused to justify prejudice and discrimination. In addition, the 1950s and 1960s brought significant advances in the natural sciences and in the social and behavioral sciences. Once again, criminologists and other scientists turned to evaluating the internal components and processes of the human body.

Genetics in Modern Biological Theories

Efforts to find a genetic explanation for violence and aggression have been met with strong resistance, primarily because of painful memories of how research linking biology and crime were used in the past (eugenics). In 1992, a conference related to the Human Genome Project at the University of Maryland had its federal funding withdrawn for attempting to discuss any particular linkage between genes and violence (Murphy & Lappé, 1994). Objections by groups who believed that any such research would be used to oppress poor and minority populations overpowered the quest for knowledge.

Although genetic research began with Mendel’s laws of inheritance, our understanding of how genes influence our behaviors is still evolving. Discovery of the genetic code in the mid-1950s took us beyond recognizing that genes were involved in heredity to a greater understanding of the process through which hereditary traits are passed from one generation to another. Part of this discovery process was the clarification of the structure and function of chromosomes, which carry human genetic material.


Human cells normally have 22 pairs of chromosomes, plus a pair of chromosomes that determines sex, for a total of 46. Sex chromosomes are termed X and Y. Females carry a combination of XX, and males carry a combination of XY. During conception, the male’s sperm carries genetic material to the female’s egg. If the sperm that fertilizes a female egg is carrying a Y chromosome, the resulting embryo will develop into a male fetus (XY). If the sperm is carrying an X chromosome, the resulting embryo will develop into a female fetus (XX).

During this process, however, things can develop abnormally. For example, during the process, some men are left with an extra Y chromosome (XYY). Erroneously termed XYY syndrome, a “supermale” carrying this chromosomal pattern usually has a normal appearance and will probably never know that he carries an extra Y chromosome, unless he is genetically tested for some other reason. Given the Y chromosome’s association with the male sex and with increased production in testosterone, many claims have been made in the research literature that XYY males are more aggressive and more violent. This supposition has not been supported with scientifically valid research.

Scientific progress made inquiry into genetic correlates of behavior more precise and less speculative. Although scholars are reluctant to associate criminal behavior with any specific gene, researchers continue to investigate the inheritability of behavioral traits. Some of the most promising work involves the study of twins and adoptees.

Twin Studies

Since Galton’s work with twins, twin studies have become more sophisticated and have attempted to respond to methodological criticisms. Distinctions between fraternal (dizygotic [DZ]) and identical (monozygotic [MZ]) twins have contributed to the sophistication of this type of research. DZ twins develop from two eggs and share about half of their genetic material, whereas MZ twins develop from a single egg and share all of their genetic material.

Twin studies attempt to control for the impact of the social environment, hypothesizing that these environments are similar for twins. Twins generally are raised in the same social environment, so the impact of the social environment is considered to be equal and consistent (and thus controlled). Therefore, any greater similarity between identical twins than between fraternal twins would provide evidence for a genetic link.

One of the earlier and simpler twin studies was conducted in the 1920s by Johannes Lange (1929). He studied 30 pairs of twins who were of the same sex. Seventeen of these pairs were DZ twins, and 13 of these pairs were MZ twins. At least one of each twin pair was known to have committed a crime. However, Lange found that both twins in 10 of the 13 MZ twin pairs were known criminals, compared with both twins in only 2 of the 17 DZ pairs.

More sophisticated and extensive studies have followed. In 1974, Karl O. Christiansen evaluated the criminal behavior of 3,586 twin pairs born in Denmark between 1881 and 1910. He found that the chance of one twin engaging in criminal behavior when the other twin was criminal was 50% among the MZ twin pairs but only 20% among the DZ twin pairs. The correlation between the genetic closeness of the biological relationship and crime was especially true for serious violent crime and for more lengthy criminal careers.

These findings were supported by additional work on the self-reported delinquency of twins in the 1980s and 1990s by David C. Rowe and his colleagues. This research found that MZ twins were more likely than DZ twins to both be involved in delinquent activity. Moreover, MZ twins reported more delinquent peers than did DZ twins (Rowe, 1983). The work of Rowe and his colleagues supported a genetic component to delinquency but also provided evidence of a social component.

Although twin studies have provided some support for a genetic component to behavior, it is difficult to separate the influence of genetics from the influence of social factors. There also are theoretical problems with the assumption that twins raised in the same home are subject to the same treatment and the same social environment. Even scholars who study the link between criminal behavior and genetics are cautious with their conclusions, arguing that these types of studies reveal only that the similarities between twins have some impact on behavior. Whether these similarities are genetic, social, or some combination of the two is still open for debate. Studies of adopted individuals constitute one attempt to resolve this issue.

Adoption Studies

In adoption studies, the behavior of adoptees is compared with the outcomes of their adopted and biological parents. The aim is to separate out the impact of the environment from the influence of heredity. This research asks whether a child will exhibit traits of the adopted parents or of the biological parents.

Research indicates that an adoptee with a biological parent who is criminal is more likely to engage in property crime than other adoptees and that this effect is stronger for boys. The findings, from a study of 14,427 Danish children adopted between 1924 and 1947, provide evidence that there may be a genetic factor in the predisposition to antisocial behavior (Mednick, Gabrielli, & Hutchins, 1984). Studies in both Sweden and in the United States confirm these conclusions.

A meta-analysis of adoption studies, conducted by Walters and White (1989), reinforced the importance of adoption studies as the best way to determine the impact of both environment and genetics on criminal behavior but also emphasized the theoretical and methodological difficulties inherent to this approach. Knowing, for example, whether an adoptive parent has a criminal history provides no information on the social environment provided in the adoptive parent’s home. The definitions of crime and criminality also widely vary in these studies and can be challenged. For example, one study may consider as criminal behaviors perhaps best classified as antisocial (e.g., using bad language, adultery). Furthermore, these studies do not account for the quantity or quality of social interactions experienced within the various settings (adoptive vs. biological). Finally, the determination that someone is a criminal simply on the basis of a conviction or incarceration is problematic and does not consider undetected criminal behaviors.

According to researchers who worked on the Human Genome Project, however, twin and adoption studies are the best source for evaluating individual differences in human behavior. Recent studies have consistently demonstrated that genetic variation substantially contributes to behavioral variation across all types of behavior. Two primary conclusions are derived from these studies: (1) Nearly all of the most frequently studied behaviors, characteristics, and conditions (e.g., cognitive abilities, personality, aggressive behavior) are moderately to highly heritable, and (2) nonshared environments play a more important role than shared environments and tend to make people different from, instead of similar to, their relatives.

Most biological scholars now cautiously conclude that there may be a genetic predisposition toward criminal behavior but that the manifestation of these predispositions is dependent on social and environmental factors. However, belief (or not) in a genetic link to criminality does not pre-clude other potential biological explanations of crime.

Biochemical Explanations: Hormones, Neurotransmitters, Diet

Another biological explanation for criminal behavior involves the body’s hormones, released by some of the body’s cells or organs to regulate activity in other cells or organs. Androgens are hormones associated with masculine traits, and estrogens are associated with feminine traits. Progesterone is another hormone associated primarily with female reproductive processes, such as pregnancy and menstruation.


Testosterone is considered the male sex hormone. Although persons of both sexes secrete testosterone, males secrete it in higher levels. Researchers have found that higher levels of this hormone are associated with increased levels of violence and aggression, both in males and females. Criminal samples have been found to have higher testosterone levels when compared with noncriminal samples, although these levels were still within normal limits.

Problems with attempting to explain criminal behavior by testosterone levels, however, are problematic. Testosterone levels naturally fluctuate throughout the day and in response to various environmental stimuli. For example, levels among athletes increase prior to competitions, perhaps indicating that testosterone is produced to increase aggression instead of as a response to aggression. This makes correlating levels to behavior and controlling for environmental stimuli extremely difficult.

Recent research conducted by Ellis in 2003, however, has added an evolutionary component. In his evolutionary neuroandrogenic theory, Ellis argued that increased levels of testosterone reduce the brain’s sensitivity to environmental stimuli, making a person act out, with reduced abilities to control emotions. He also speculated that the development of testosterone’s “competitive-victimizing” effects is the result of natural selection, as described by Darwin.

Scholars who study the relationship between testosterone levels and crime cite as support the differences between males and females in terms of levels of crime in general and levels of violence in particular. This work has led to the “treatment” of male sex offenders with chemical derivatives from progesterone to reduce male sexual urges through the introduction of female hormones (e.g., Depo-Provera, a brand of birth control for women). This has been effective in reducing some types of sex offenses (e.g., pedophilia, exhibitionism), but it has had little or no impact on other crimes or violence.

Premenstrual Syndrome and Premenstrual Dysphoric Disorder

Researchers also have investigated the impact of female hormones on behavior in women, beginning with two English cases in 1980 in which two women used premenstrual syndrome (PMS) as a mitigating factor in violent offenses. These efforts led to female defendants in the United States being able to argue reduced culpability due to PMS.

More recently, a more severe form of PMS has been identified. Premenstrual dysphoric disorder (PMDD) is a severe and debilitating form of PMS, distinguished by the level of interference the menstrual process has on the ability of the woman to engage in the functions of everyday life. Interestingly, researchers have established a genetic link to the development of PMDD. Women with a certain genetic structure have increased (abnormal) sensitivity to their own normal hormones, resulting in increased symptoms of emotional and physical stress.

Another phenomenon associated with female hormones is postpartum depression syndrome. Although most new mothers experience symptoms of depression in the weeks or months following birth, which is primarily thought to be due to a decrease in progesterone, approximately 1% to 2% of these mothers exhibit severe symptoms, such as hallucinations, suicidal or homicidal thoughts, mental confusion, and panic attacks. As with PMS and PMDD, postpartum depression syndrome has successfully been used as a mitigating factor in the legal defense of women accused of crimes while suffering from its effects. Both PMS and PMDD, however, are controversial concepts, difficult to diagnose as medical conditions, and argued by some to be social constructions and psychiatric problems instead of medical conditions.


In addition to the possibility that human hormones may directly impact behavior, they also may directly impact chemicals that regulate brain activity. Neurotransmitters are chemicals that transmit messages between brain cells, called neurons, and have a direct impact on the many functions of the brain, including those that affect emotions, learning, mood, and behavior. Although researchers have extensively studied more than 50 of these chemicals, research on the biological bases of crime has focused on three of these: (1) norepinephrine, which is associated with the body’s fight-or-flight response; (2) dopamine, which plays a role in thinking and learning, motivation, sleep, attention, and feelings of pleasure and reward; and (3) serotonin, which impacts many functions, such as sleep, sex drive, anger, aggression, appetite, and metabolism.

High levels of norepinephrine, low levels of dopamine, and low levels of serotonin have been associated with aggression. Results from research that has examined the impact of these neurotransmitters are mixed. With all of these chemicals, fluctuations in their levels may result in certain behaviors, and certain behaviors may contribute to fluctuations in their levels (in a reciprocal interaction effect).

Although there is little doubt that there is a direct relationship between levels of various neurotransmitters and behavior, this relationship is extremely complex and nearly impossible to disaggregate. Chemical changes are part of the body’s response to environmental conditions (e.g., threats) and to internal processes (e.g., fear, anxiety), and environmental conditions and internal processes produce chemical changes in the body. This creates a chicken-and-egg question about whether our responses and reactions are the result of changes in our chemistry or changes in our chemistry are the result of our responses and reactions.

Diet, Food Allergies, Sensitivities, Vitamins, and Minerals

What one eats impacts one’s body chemistry. High-protein foods, such as fish, eggs, meat, and many dairy products, contain high levels of the amino acid tryptophan. Tryptophan produces serotonin (see preceding section). Another amino acid, tyrosine (also found in high-protein foods), is related to the production of both dopamine and norepinephrine. These relationships have suggested that many aggressive behaviors may be controlled with a diet higher in protein and lower in refined carbohydrates.

Carbohydrates—specifically, refined carbohydrates, such as white refined flour, white rice, white refined sugar, and any processed foods with high levels of sugar—also are examined as related to problem behavior. Complex carbohydrates are slowly transformed into glucose, which stimulates the production of insulin in the pancreas, which in turn produces energy for the body. Simple or refined carbohydrates are not processed slowly and result in the rapid release of insulin into the bloodstream, causing a sharp decrease in blood sugar, depriving the brain of the glucose necessary for proper functioning. This sharp decline in blood sugar also triggers the release of hormones such as adrenalin and increases in dopamine. This combination has been associated with increased aggression, irritability, and anxiety.

The state of having chronically reduced blood sugar caused by the excessive production of insulin is called hypoglycemia. Individuals who are hypoglycemic experience increased levels of irritability, aggression, and difficulty in controlling their emotional expressions. Hypoglycemia has successfully been used to mitigate criminal behavior. The most infamous example occurred during the late 1970s when Dan White killed San Francisco Mayor George Moscone and City Supervisor Harvey Milk after consuming nothing but junk food such as Twinkies and soda for several days. At trial, White’s attorney successfully argued that White suffered from “diminished capacity” due to his hypoglycemia. His argument has come to be known as the “Twinkie Defense” (Lilly, Cullen, & Ball, 2007).

Experimentation with the diets of criminal populations have indicated that reducing intake of refined carbohydrates and increasing consumption of fruits and vegetables have significantly decreased behavioral problems and disciplinary write-ups. It is difficult, however, to separate the impact of diet from other potential factors that may affect behavior.

Other potential contributors related to food intake involve food allergies and the consumption (or not) of various vitamins and minerals. Once again, refined carbohydrates may be a culprit. These types of foods contain particularly high levels of cadmium and lead, two minerals known to cause damage to brain tissue and impact the production of neurotransmitters.

Several food components have been associated with reactions that may include aggressive, violent, or criminal behavior. Some people may be allergic to or exhibit increased sensitivity to chemicals contained in chocolate (phenylethylamine), aged cheeses and wine (tyramine), artificial sweeteners (aspartame), and caffeine (xanthines).

Others may react to food additives, such as monosodium glutamate and food dyes. Criminal populations also have been found to lack vitamins B3 and B6 in comparison to noncriminal populations.

Environmental Toxins

The frontal lobe of the brain, an area that has become the focus of biological investigations into criminal behavior, is particularly sensitive to environmental toxins, such as lead and manganese. Behavioral difficulties, such as hyperactivity, impulsivity, aggression, and lack of self-control, have been associated with increased levels of these heavy metals.

Examination of the impact of environmental toxins on human behavior is very promising because it integrates biological with sociological and criminological theories. Facilities that produce, store, treat, and dispose of hazardous wastes are largely to blame for the production of environmental toxins. Research has shown that proximity to these types of facilities increases the impairment of the brain and of the general central nervous system, producing lower IQs; reductions in learning abilities, frustration tolerance, and self-control; and increases in impulsivity, hyperactivity, antisocial behaviors, violence, and crime.

Researchers who study the relationship of environmental toxins to crime argue that our environment is producing crime by producing neurological damage. Scholars emphasize the fact that minority populations and lower-income groups are the ones most likely to live near these facilities and as a result are more likely than white and higher-income groups to be negatively impacted by these toxins. This, according to the researchers, may help explain why minorities and people from the lower classes seem to catch the attention of the criminal justice system in higher rates than others.

Brain Structure and Function

Whereas earlier biological theories considered the brain to be an organ with various areas of specialized function, modern theories recognize that the brain is a complex organism. Some areas of the brain are associated with specific functions (e.g., speech and vision), but all areas of the brain work together, and a problem or event in one area inevitably affects other areas. Although our understanding of the brain’s structure and function has significantly advanced, we still know little about the relationship between the brain and many behaviors, such as those related to crime. In addition, we know little about how the environment affects the brain’s structure and function.

The frontal lobe and the temporal lobe are two parts of the brain examined by researchers interested in criminal behavior. The frontal lobe is responsible for regulating and inhibiting behaviors, and the temporal lobe is responsible for emotionality, subjective consciousness, and responses to environmental stimuli.

Tools to evaluate brain structure, brain function, and behavior rely on sophisticated medical equipment and measurements, such as electroencephalography, computed tomography, magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography. These devices have been used by researchers to compare the brain structures and brain functions between criminal and noncriminal populations. In addition to providing images of structure, many of these technologies can track real-time changes in the brain’s neural activity before, during, and after exposure to physical or emotional stimuli.

Preliminary studies indicate that the brains of violent offenders and the brains of other individuals differ in both structure and function, but many of the studies have relied on very small sample sizes, which reduces the generalizability of these findings. Moreover, these studies also are plagued by questions of whether the brain causes the violence or whether violence results in changes to the brain. Evidence of structural or functional abnormalities in the brain has, however, resulted in the mitigation of criminal offenses, such as reducing charges of murder to manslaughter.

Studies of brain development have shown that early and chronic exposure to stress (e.g., abuse, neglect, violence) may cause physiological changes in the brain that impact the way a person responds to stress. Human brains under stress produce the hormone cortisol, which helps to return body functions to normal after a stressful event. However, repeated exposure to cortisol may result in decreased sensitivity to its effects and either contribute to criminality or contribute to a person’s acceptance of being victimized. In addition, this research is supported by studies on the brain development of children raised in high-stress environments (inner city, urban, high-crime areas) that found enhanced fight-or-flight impulses among these children.

A recent study by Diana Fishbein in 2003 concluded that behavioral problems may originate in the hypothalamic-pituitary-adrenal axis (HPA) that connects the brain to the adrenal glands, which regulate the production of important hormones. Fishbein claimed that increased levels of cortisol, produced in response to stressors, cause the HPA to shrink and become ineffective. An ineffective HPA depletes cortisol and results in the inability to regulate emotions and behavior. A dysfunctional HPA may be caused by stress in childhood that impedes its development, or it may be caused by damage later in life.

Biosocial Perspectives

Some scholars who study criminal behavior began to synthesize sociological perspectives with biological perspectives. One of the most influential publications in this area was Sociobiology: The New Synthesis, written by E. O. Wilson in 1975. Wilson was among the first criminologists to express disillusion with current sociological and behavioral theories by emphasizing that an individual was a biological organism operating within social environments. Publications by Dawkins in 1976 (The Selfish Gene) and by Ellis in 1977 (“The Decline and Fall of Sociology, 1975-2000”) illustrated criminological disillusion with purely sociological explanations and renewed hope for improved biological perspectives that would not operate under the faulty assumptions of earlier biological research. Major scientific developments from the 1950s to the mid-1970s (e.g., in the study of genetics) also contributed to the resurgence of interest in explanations of behavior with biological bases. Other advances in the mid- 1980s led scholars to examine the brain more closely as a potential factor in criminal behavior.

Modern biosocial theories attempt to integrate beliefs about the sociological development of behavior (i.e., social learning, conditioning) with the biological development of the individual who engages in behavior. In contrast to earlier biological theories that imply the heritability of behaviors, biosocial theories suggest there may be a genetic predisposition for certain behaviors.

These predispositions are expressed in terms of biological risk factors associated with increased probabilities of delinquency and crime when paired with certain environmental (social) conditions. Various risk factors that have been evaluated include IQ levels and performance, attention deficit hyperactivity disorder, and conduct disorder. Although low IQ is not directly associated with crime or delinquency, individuals with lower IQs may experience frustration and stress in traditional learning environments, resulting in antisocial, delinquent, or criminal behaviors. A diagnosis of attention deficit hyperactivity disorder also has been associated with increased levels of delinquent and criminal behavior. However, some scholars point out that this is true only for individuals who also are diagnosed with conduct disorder. Both disorders can be traced to abnormalities in the frontal lobe, so it is difficult to disentangle the relationship of each to undesirable behaviors.

In contrast to risk factors that may enhance the probabilities of an individual engaging in delinquency and crime, biological protective factors, such as empathy, may inhibit this development. Empathy is the ability of one person to identify with another person and to appreciate another person’s feelings and perspectives. Research has indicated that empathy is largely (68%) inherited. This biological tendency may counter the impact of biological risk factors. Research on these inhibiting protective factors is still quite sparse but may help explain why some people who have genetic predispositions toward delinquency and crime refrain from those behaviors.


Biological theories have evolved significantly with advances in our theoretical understanding of human behavior and in our technological capabilities of measuring human biological characteristics and processes. Whereas earliest attempts to understand the relationships between biology and behavior focused on the outwardly observable, modern efforts are looking inward, to the chemical and structural foundations of our bodies. Contemporary biological theories also recognize the interactive relationship between internal biological events and external sociological events. Moreover, increasing awareness of the complex interrelationships among our environment, our biology, and our behavior is contributing to the development of a rich and promising epistemology of criminal behavior.

Our scientific advancements, however, still have not reached the level where we can definitively determine that antisocial, deviant, or criminal acts have biological roots or correlations. Increasing awareness of how our genes pass along (or do not pass along) our behavioral characteristics, of how our brain structures and functions are interrelated, of how our body chemistry affects and is affected by our behavior and reacts to environmental stimuli, and of how our development in a social environment impacts all of these biological processes will bring us closer to being able to predict behavior and therefore being able to better control it.

Care must be taken to separate the act from the actor and to avoid the atrocities of the past. As our ability to determine biological correlates of behavior expands, so too does the danger of using such information in unethical and inhumane ways that would stigmatize or punish people on the basis of what prohibited behaviors their biological profiles suggest they might do. It is hoped that progress in these areas of inquiry will parallel corresponding advances in our capabilities to prevent initial undesirable behaviors and to treat individuals who do behave undesirably because of biological or biosocial influences.