Robert G Goldstein. Skeptic. Volume 21, Issue 1. 2016.
The invention of the microchip has transformed molecular biology, yielding great progress in genomic medicine-especially in fields such as oncology and infectious disease. Unraveling the genetic underpinning of mental illness, however, has proved more daunting. This is hardly surprising, as many psychiatric disorders are highly heterogeneous and therefore difficult to link to specific genes. Further, most behavioral traits are likely polygenic-that is, controlled by many interacting genes. But despite slow progress in the area of behavioral genetics, psychiatry-after many decades lost in the wilderness-has benefited enormously from advances in neuroscience and has established itself as an empirically based medical discipline.
Unfortunately, psychoanalysis dominated American academic psychiatry during the middle decades of the twentieth century. Although it has since lost much of its influence, psychoanalytic thinking did much to obscure the prominent role of genetics in mental illness. Furthermore, despite significant advances in our understanding of the biological bases of behavior, psychoanalytically-tinged thinking has stubbornly hung on-having so thoroughly infected Western culture and folk-psychology. (Superstition, it has been said, may assume many disguises.) Large segments of the population, including many therapists, still assume a person’s behavioral problems and proclivities are predominantly shaped by one’s close relationships and “formative” experiences. In therapists’ offices throughout the world a watered-down version of Freud’s approach often still plays some role in the therapeutic process, as the patient (with the therapist’s guidance) concocts a “how-the-leopardgot-its spots” story of his or her current difficulties. We now know, however, that the mind is not structured along narrative principles but rather according to the laws of natural selection-from a blueprint written in digital code, composed of the base pairs that constitute our genetic endowments.
While Freud was on the continent developing that prodigally creative but highly fanciful blend of nature philosophy, philology, and crypto-science he would call psychoanalysis, across the channel in the English countryside, the true scientific revolution led by Charles Darwin had already taken shape. Darwin’s theory of natural selection is generally thought to focus chiefly on the evolution of physical characteristics and the differentiation of species; however, Darwin showed a keen interest in behavior throughout his career-from the chapter on instinct in The Origin of Species to the two major works that are in good measure devoted to the study of behavior (The Descent of Man and The Expression of the Emotions in Man and Animals). Less well known is the important role that Darwin’s cousin, Sir Francis Galton, played in the Darwinian revolution. Galton explicitly tried to extend Darwin’s project by undertaking the first empirical studies of the inheritance of mental characteristics in humans; in doing so, he became the founder of the discipline known today as behavioral genetics.
I have often wondered when the idea first took hold of Galton: that the lineaments of our destinies lay buried in our forbearers’ graves; that one is born, in a sense, fully formed according to the laws of a yet undiscovered science-the earliest particulars of which would soon be illuminated by a Moravian beekeeper named Mendel. Perhaps it was during that dreary November in 1840 while he was a student at Cambridge. He was a callow first-year but he knew one thing for certain: he was quite unwell. The rigors of academic life (mathematics in particular) had caused him to take to bed-the first in a series of mental collapses. I imagine it was then that Galton first began to wrestle with the enigma of temperament and its transmission through the generations. Maybe it was the shape of his thin, tight-set mouth that reminded him of a close relation-one who had also suffered bouts of nervous exhaustion. Perhaps, immobilized in a bath growing lukewarm he thought: someone who came before me must have experienced this exact cast of mind-this “mill… working inside my head.” He would recover and go on to complete his degree but the riddle of inheritance would occupy him for a lifetime. The youth, who was driven to bed by the calculus, would go on to become founder of the discipline of biostatistics, a close collaborator of Darwin and a prodigiously inventive scientist in his own right.
Today, however, Francis Galton is virtually unknown outside of scientific and historical circles. Among his many contributions were the forensic use of fingerprints, the concept of regression to the mean, and the first empirical studies of twins. But Galton’s greatest achievement remains his prescient ideas on the inheritance of behavioral traits. Long before there were any credible notions regarding the mechanisms of heredity, Galton set out to prove that personality, temperament, and intelligence were every bit as heritable as curly hair, blue eyes, and a high forehead. Thus it is that the modern discipline of behavioral genetics-which uses molecular and population approaches to parse the Gordian knot of human temperament-emerged from the work of this shy, eccentric Victorian.
Parentes Peremptores: A Science of Rational Breeding
Gabon’s relative obscurity may stem from his role as a pioneer of eugenics-the effort to ameliorate social and medical ills by influencing who gets to reproduce. Given the moral hazards inherent to eugenics (as well as its more sinister fellow-travelers later in the twentieth century), it is not surprising that Gabon’s stature suffered as a result of his political views. To make matters worse, Gabon’s intellectual gifts were alloyed with decidedly odd personality traits-including an obsessive drive to quantify the most trivial variables. Indeed, his was a career that encompassed extremes of fatuity and inspiration. He developed methods that would form the foundations of population genetics, but he also undertook experiments on tea brewing, gave hearing tests to the occupants of the London Zoo, and was the author of the 1896 article entitled “Three Generations of Lunatic Cats.” In his personal life he was, as his biographer Martin Brookes describes, “an immense snob”…. who wished to turn marriage into a “rutting club” for the elite and “a stud farm for intellectuals.”
Belief in selective breeding was not, strictly speaking, a nineteenth-century notion. One can find evidence of it in folk psychologies throughout the world and across the centuries. The conviction that children will carry forward the pathologies in their families of origin may underlie, along with economic considerations, the custom of arranged marriage-a custom that constitutes the world’s oldest and most common eugenic practice. The encyclopedic Renaissance treatise on mental infirmity, Robert Burton’s 1621 The Anatomy of Melancholy, illustrated the prevailing, pre-scientific assumption that temperament and mental illness were inherited; it also contains arguments in favor of selective breeding: “For now… in giving way to all to marry that will… there is a vast confusion of hereditary diseases…. It comes to pass that…we have many feral diseases raging amongst us, crazed families, parentes peremptores [our parents are our ruin], and our fathers bad, and we are likely to be worse.”
Galton, then, was following in an age-old tradition of viewing mental traits no differently from physical ones. Perhaps Galton should not be too harshly judged for his faith in eugenics. The Victorians, like those of Burton’s era, had no effective treatments for mental illness. Tallying up the incidences of the major mental disorders quickly reveals the tremendous burden that these maladies placed on families and communities. Because of this, enthusiasm for eugenics was not restricted to conservatives. George Bernard Shaw was a fan of Gabon’s work and viewed eugenics as essential for the preservation of civilization. In this light, Shaw’s literary send-ups of human courtship can also be viewed as cautionary tales revealing romantic love to be a flawed method of breeding. Infatuation-as a paradigm of human folly-surely offered the playwright a broad comedic target, but on the species level Shaw viewed it as something akin to entrapment. Like Galton, Shaw looked forward to a rational system of human reproduction. The narrator’s tongue-in-cheek comments in Shaw’s The Revolutionist’s Handbook and Pocket Companion were probably not far removed from Galton’s views: “Even a joint stock human stud farm (piously disguised as a reformed Foundling Hospital or something of that sort) might well, under proper inspection and regulation, produce better results than our present reliance on promiscuous marriage.”
It is more accurate, then, to view Gabon guilty not of political extremism but scientific idealism. As evinced by Shaw’s comments, this is a charge that could have been leveled at those of the left as well as the right in the late nineteenth century-a time of progressive movements of every stripe. But this eccentric idealist also played a significant role in the Darwinian revolution by developing statistical approaches to inheritance and by undertaking the first empirical studies to prove the inheritance of mental traits.
An Informational Concept of Heredity
Galton realized that the inheritance of complex traits appeared “capricious” at the level of individual families. Clues to the rules and mechanics of heredity could only be revealed through a change in scale-by scrutinizing patterns of inheritance in large populations. Galton subjected all sorts of traits to statistical analysis: height, arm strength, the speed at which word associations were generated. But his main interest, as a eugenicist, was charting variation in human mental abilities. In his 1865 paper “Hereditary Talent and Character,” Galton tried to show that intellectual gifts were heritable by demonstrating that talent clustered in families. By studying persons of exceptional talent (in fields least impacted by nepotism), Galton created a statistical lever of sorts that could yield significance despite a thicket of confounding variables. Like a lot of Galton’s work, this paper contained methods that were at once crude and inventive; nonetheless, the results are difficult to attribute to chance alone. He estimated that Europe had produced 330 individuals of prodigious literary and scientific genius over the preceding four centuries out of a total of approximately one million highly educated persons. This yielded a “genius incidence” of roughly one per 3000. However, of these 330 geniuses, 51 (approximately one sixth of them) also had a close blood relative with exceptional gifts. This represented an odds ratio of 465-that is, a close relation of a creative or scientific genius would be 465 times more likely to possess great talent than any unrelated but highly educated individual.
Although Galton focused on population-based methods to prove the heritability of mental traits, he understood that any workable theory of heredity also had to be able to account for individual exceptions to the trend seen in groups. Why, for example, did two gifted parents frequently produce unexceptional offspring? In fact, as Galton observed, parents who showed extreme variation in a particular trait often produced children who showed less variation from the mean than their parents. He dubbed this statistical phenomenon “regression to the mean” and postulated that it arose because of the way heredity operated-namely, children were not a blend of their parents’ features but instead derived their traits from a population of ancestors stretching back over the generations. The collective genetic legacy of these ancestors pushed the offspring of outliers back toward the mean.
Galton’s effort to explain regression to the mean led him to a related discovery-his theory of “the ancestral law,” which posited that offspring often possessed traits not found in their parents but which were present in more distant ancestors. This implied a distinction between phenotype and genotype-a distinction that the Danish botanist Johansson more explicitly elucidated. Galton’s concept of ancestral inheritance was prescient in other respects as it implied that the germ cells contained a storehouse of particulate information which made its way down the generations unaltered-sometimes going unexpressed, other times popping up in an unpredictable fashion. According to Galton’s notion of reversion, offspring were not so much the product of two parents but rather the descendants of a chain of ancestral embryos.
Galton’s ideas on inheritance predated the rediscovery of the work of Mendel, yet his speculations were quite insightful for a man stumbling about in the dark. His notion of particulate units of heredity-carriers of information that could remain latent or be expressed, that were segregated from somatic influence precisely because they were fundamentally of a different nature than the structures they instantiated-prefigured aspects of August Weissmann’s theory of the “continuity of the germ plasm,” which is generally regarded as the first purely informational concept of inheritance.
Oxen, Twins, and Ill-tempered Families
Galton’s work was also influenced by Darwin’s research on animal behavior. Both men viewed the highly species-specific behaviors found in various animals as proof of the heritability of even the most complex behavioral repertoires. Galten was particularly interested in the social behavior of domesticated animals and cited the limited number of species that could be domesticated as proof of the innate nature of behavior: “only a few species of animals are fitted by their nature to become domestic, and .. .these were discovered long ago through the exercise of no higher intelligence than is to be found among barbarous tribes of the present day…. All the suitable material whence domestic animals could be derived has long since been worked out…. The finality of the process of domestication must be accepted as one of the most striking instances of the inflexibility of natural disposition.”
To Galten, people were fundamentally no different from oxen: some were pleasant, agreeable and easily led; others were obstinate and quarrelsome. Long before the scientific age, people had no trouble distinguishing the various dimensions of temperament and the basic human personality types. Although these types were easy enough to spot, the empiric study of personality and its inter-generational transmission was certainly beyond crude nineteenth century science; true to form, Galten dove right in. In his 1887 study, “Good and Bad Temper in English Families,” Galten gathered narrative descriptions of informants’ family members, which he had obtained by survey, and turned these descriptions into categorical data in order to measure correlation of temperament within families. Many of the negative traits approximate the modern psychiatric criteria for the more severe personality disorders with an added sprinkling of mood symptoms. The ill tempered were described as “acrimonious, rageful, arbitrary, capricious, impetuous, easily-offended, despotic, irritable, vindictive.” In short, this group represents that five percent of the population that, while not acutely mentally ill, makes the rest of humanity miserable. Galten believed that these sullen, ungovernable people were the scourge of domestic tranquility-adding to the societal ills of violence, pauperism, and debauchery.
Galten predicted that looking across many families would reveal patterns of family transmission that were not necessarily apparent when examining individual families due to the tendency of offspring to display traits inherited from more distant relations. Out of the approximately 70 families that he studied, he found that good tempered offspring were three times more likely to emerge from good tempered parents than from bad tempered parents. From the union of two bad tempered parents, there was a greater than ten to one ratio of ill to good tempered children.
Galten knew that studies of temperament were open to criticism, given the difficulties of controlling for the influence of environment. He realized that twins represented a unique opportunity for resolving this dilemma. In 1875, Galten undertook the first twin study described in the paper “The History of Twins, as a criteria of the Relative Powers of Nature and Nurture.” Despite a purely anecdotal approach, a lack of access to twins raised apart, and Galton’s poor understanding of the distinction between mono and dizygotic twins, the paper is filled with uncanny insights. Galten followed the development of 35 pairs of identical twins and 20 pairs of dissimilar twins who, like regular siblings, had quite distinct temperaments. He found that the identical twins remained extremely similar in temperament even as they grew older and were exposed to varying influences outside the home. As borne out in modern twin studies, Galten discovered that identical twins actually seemed to converge as they aged as time brought out “hidden weaknesses in their constitutions.” Regarding the impact of a shared environment upon the dissimilar twins, Galten found that without exception there seemed to be little convergence in those born with distinct temperaments despite being subject to the same school and home environments. Galten concluded “there is no escape from the conclusion that nature prevails enormously over nurture when the differences of nurture do not exceed what is commonly to be found among persons of the same rank of society and in the same country.”
Interestingly, here Galten appeared to give a passing nod to the impact of environment by noting that environment will count for little as long as it is reasonably typical-therefore implying that exceptional environments might have a significant impact. This nicely anticipates modern studies of I.Q. that suggest that social class negatively impacts on I.Q. scores under conditions of deprivation, but that once the environment achieves adequacy, the main determinant of I.Q. reverts to genetic endowment. Remarkably, Galton also perceived a critical reason why genetic transmission can easily be confused with environmental influence:
Much stress is laid on the persistence of moral impressions made in childhood, and the conclusion is drawn, that the effects of early teaching generally, must be important in a corresponding degree. I acknowledge the fact, but doubt the deduction. Its parents usually teach the child, and their teachings are of an exceptional character, for the following reason. There is commonly a strong resemblance, owing to inheritance, between the dispositions of the child and its parents. They are able to understand the ways of one another more intimately than is possible to persons not of the same blood, and a child instinctively assimilates the habits and ways of thought of its parents. Its disposition is educated by them, in the true sense of the word; that is to say, it is evoked earlier than it would otherwise have been.
Here Galton appears to anticipate the contemporary notion of a dynamic interaction between genes and environment, with genetic endowment playing a role in conditioning the experience of environment. This may also help to explain why monozygotic twins tend to show greater similarity as they age and dizygotic twins less so. Darwin, himself, eventually weighed in on the relative contributions of nature and nurture, indicating in his autobiography that he agreed with Galton that psychological traits were largely innate, environment playing only a minor role.
Galton might have been disappointed by the findings of modern twin research that suggest a significant role for environmental influence; in many behavioral domains, monozygotic twins only show a concordance of 0.4 to 0.7. However, as we also now know, this concordance ratio does not vary whether twins are raised together or apart; therefore “shared environment” (Galton’s nurture) appears to contribute slightly if at all to the degree of behavioral commonality found in identical twins. Galton would have no doubt felt vindicated by this finding as it is now generally accepted that the 30 to 50 percent that is considered nonheritable cannot be attributed to the shared environment but to each individual’s personal course (the socalled “non-shared” environment) as well as to complex developmental contingencies. A number of these developmental contingencies, such as epigenetic effects (factors that determine how or when genes are transcribed), fall between traditional notions of the genetic and the environmental as they may be influenced by stochastic as well as environmental factors. Such epigenetic effects, as well as other non-sequence based variability in gene expression, help explain why concordance rates for complex traits could never approach 100 percent.
Galton’s hereditarian enthusiasms were no doubt tainted by elitism and racism; he was-as we all are-a product of his times. Nonetheless, his remarkable insight and ingenuity lent scientific credence to what common people have known for millennia; namely, human offspring closely resemble their forbearers both mentally and physically. He sought to debunk the common-sense assumption that emotional make-up was, to a significant degree, the byproduct of emotional experience. Although Galton’s era witnessed the apogee of the novel and the invention of “the talking cure,” this Victorian decided that, in certain domains, narrative was perhaps overrated.