Larry Arnhart. Perspectives on Political Science. Volume 34, Issue 3. Summer 2005.

The most obvious facts of human identity are sex and age. The first things we notice about people are that they are either male or female and either young or old. Human social life is shaped by the consequences of these natural facts. The natural desire of men and women for sexual mating, the natural reproduction of the young through that mating, the natural need of the young for parental care, and the natural division of labor between fathers and mothers in producing, nurturing, and educating the young—these facts of human nature shape every human society. These biological inclinations of human nature would seem to constitute the minimal core of a natural law that we can all recognize.

And yet, some people would say that even these apparently most natural facts of human life are actually social constructions-malleable conventions or customs of social life that can be changed for the sake of social reform. From the time when Plato wrote The Republic to the present, there have been many Utopian projects designed to abolish sex differences and parent-child bonding. However, the failure of those schemes confirms the stability of these natural biological facts as the basis of natural law.

Quoting Justinian’s Institutes, Thomas Aquinas spoke of natural law as “that which nature has taught all animals,” because it conforms to natural biological desires such as self-preservation, sexual union, parental care of the young, and living in social groups. Aquinas believed that “something is good insofar as it is desirable,” and, thus, that the natural goods could be known through reason’s grasping of the natural desires or inclinations as good.

The biological character of Aquinas’s reasoning about natural law is evident in his account of sex, marriage, and familial bonding. He spoke of the disposition to marry as a “natural instinct of the human species,” and he insisted that in regulating marriage, “positive laws should proceed from the instinct of nature.” He compared human beings with those animals whose offspring could not survive or flourish without extensive parental care. The primary natural end of marriage is to secure the parental care of children. The secondary end is to secure the conjugal bonding of male and female for a sexual division of labor in the household. Comparing human marriage with the mating systems of other animals, Aquinas judged every form of human sexual mating as natural or unnatural depending on how well it satisfies the natural desires for parental care and bonding of male and female.

In recent decades, proponents of sociobiology and evolutionary psychology have applied Darwinian biology to the explanation of human nature. A few people—myself included—have argued for a revival of natural law reasoning rooted in Darwinian theory. Conservatives such as James Q. Wilson and Francis Fukuyama have claimed that this reasoning provides scientific confirmation for the conservative understanding of natural law as supporting the traditional morality of marriage, family life, sexual differences, and social order generally.6 Wilson and Fukuyama have pointed to the breakdown of social order in the 1960s-with rising rates of crime, divorce, and single-parent families-as showing the disastrous consequences of rejecting conservative moral norms. But at the same time they have predicted a restoration of those norms that would show them to be rooted in the spontaneous order of human biological nature.

Yet, conservatives are ambivalent about Darwinian biology. On the one hand, they like the idea of rooting traditional morality in human biological nature. On the other hand, many conservatives are deeply suspicious, if not scornful, of Darwinian science because they think it promotes materialism and atheism. This suspicion of Darwinism has led many conservatives to embrace “intelligent design theory” as an alternative to Darwinian science.

This conservative ambivalence about Darwinian natural law is clear in the debate over the nature of sex differences. Liberals tend to agree with the gender-feminist assumption that the behavioral differences between men and women are mostly social constructions rather than natural propensities, and that as social constructions, they can be changed by social policy to promote an ideal of sexual equality in which sex differences would disappear. But conservatives are inclined to believe that many of the traditional differences between men and women are manifest in their biological natures and cannot be radically changed, and that the attempt of social policy to bring about an androgynous society must bring emotional harm and social disorder.

To support this stance, conservatives have often adopted Darwinian arguments about how evolution by natural selection has shaped the biological differences between men and women. Men have evolved to be more aggressive, dominant, and sexually promiscuous than women, whereas women have evolved to be more nurturing and more inclined to childcare. Men compete with other men for sexual access to physically attractive women, whereas women compete with other women for marriage to men willing and able to invest resources in their children. The violent aggressiveness of young men becomes socially destructive when it is not domesticated by marital and familial duties. Conservatives believe, therefore, that a fundamental concern of traditional morality is to use marriage to put men under the civilizing influence of wives and children.

This dispute between those on the Left who think sex differences are socially constructed and those on the Right who think sex differences are biologically natural is at least two centuries old. Socialists have tried to establish absolutely egalitarian societies in which marriage and private families would disappear and where men and women would become indistinguishable. The conservative opponents of such utopian projects have criticized them as contrary to human biological nature and thus contrary to natural law. So, for example, in Socialism-first published in 1922-Ludwig von Mises agreed with the liberal feminists who argued that men and women should be equal under the law, but he disagreed with the socialist feminists who argued for abolishing sex differences. “It is a characteristic of socialism,” Mises observed, “to discover in social institutions the origin of unalterable facts of nature, and to endeavour, by reforming these institutions, to reform nature.”

In response to a new wave of radical feminism in the 1960s and 1970s, conservatives argued for the naturalness of sex differences by appealing to Darwinian biology. In the early 1970s, books by Steven Goldberg and George Gilder on the biological nature of sex differences supported the traditional conservative morality of sex and marriage. Goldberg stressed the male desire for dominance that explained why there has never been a truly matriarchal society. Gilder stressed the turbulent aggressiveness of young unmarried males and their need for the civilizing effects of marriage. In the 1990s, conservatives cheered Camille Paglia’s zesty attack on the feminist assumption that sex differences were cultural artifacts rather than biological facts. Later, conservatives like Christina Hoff Sommers made the case for respecting the natural sex differences in the moral education of boys and girls.

Most recently, Steven Rhoads’s book Taking Sex Differences Seriously has continued this tradition of conservative reasoning about the biological nature of sex differences. Against gender feminists’ claim that sex differences are mostly “socially constructed” and, thus, subject to change through social policy, Rhoads argued that men and women differ by nature because their biological natures incline them to have different preferences, abilities, and interests. Compared with women, men tend by nature to be more aggressive, dominant, and sexually promiscuous. Women tend by nature to be more nurturing, more attentive to children, and less physically aggressive. Most women find their greatest happiness in being married and having children. Men are less inclined to commit themselves to marriage and parental care, although in the long run, men are generally happier when their restlessness has been calmed by marriage and children.

Rhoads surveys various kinds of scientific research suggesting that these sex differences are rooted in biological nature. Most often, he cites research about the differing hormonal constitutions of men and women-for example, men having higher levels of testosterone and women having higher levels of estrogen-which promote different patterns of behavior in men and women. He also employed research on biological development to show how sex differences arise in fetuses and infants, research in neuroscience to show how sex differences show up in the brain, and research on animal behavior to show how sex differences arise in other animals closely related to human beings. He also refers repeatedly to research in evolutionary psychology that explains how these biological sex differences could have been shaped by natural selection in the evolutionary history of the human species. So, for example, if the reproductive fitness of males was enhanced by their being more sexually promiscuous and more physically aggressive than females, and if the reproductive fitness of females was enhanced by their being more selective in their mating and more attached to children, then it is likely that natural selection would have shaped the human species to show such sex differences.

The debate over whether sex differences are socially constructed or biologically natural has implications for social policy. Rhoads’s primary illustration is the federal policy in the United States concerning the participation of men and women in sports. Title IX of the Education Amendments of 1972 prohibits sex discrimination in athletics in publicly funded schools. The Department of Education has interpreted this to require that the proportion of male and female athletes should conform to the proportion of men and women in the student body as a whole. Men tend to be more interested than women in participating in intercollegiate sports. The feminist proponents of Title IX assume that this is a consequence of a discriminatory culture that discourages women from being interested in athletics, and, therefore, changing the cultural environment to encourage female athletes will eliminate this sex difference. Although the number of women participating in intercollegiate sports has increased, the Title IX requirements have forced the elimination of many men’s teams in many sports because the number of men interested in athletics still tends to be greater than the number of women. Rhoads argues that this difference is a part of biological nature because men are biologically inclined to have a greater interest in the aggressive competition of athletics than do women, although many women are attracted to sports such as gymnastics, tennis, and cheerleading. Moreover, male athletics is important for social order because it channels male competitiveness in ways that promote the formation of good male character.

The reviews of Rhoads’s book in conservative publications have been enthusiastic in their praise. And yet, one can detect an uneasiness about Rhoads’s reliance on evolutionary biology. For example, Harvey Mansfield, writing in the Weekly Standard, suggested that “taking sex differences seriously” means that rather than viewing them as “socially constructed,” we need to trace them back to “unchangeable nature.” But “we no longer have a way of understanding the permanent structure of things as nature.” Evolutionary theory does not satisfy this need, because “evolution suggests that nothing is permanent and everything is constructed over time, only very gradually and in a sense not by human choice.” Darwinian science teaches us that “we are progressive beings full of hope for a better future but fitted out with conservative natures made long ago that constitute a heavy drag on our hopes.”

Mansfield went on to observe:

What evolutionists think is the closest we usually get to the notion of nature these days. But it is not close enough. For evolution sees everything as organized for survival and cannot recognize our better, higher nature. Thus it sees no difference in rank between the male desire for an active sex life and the male interest in being married, or between the promptings of desire and the instruction of reason.

Mansfield suggested that Rhoads implicitly recognized these problems by speaking of what “evolutionists think” without ever explicitly declaring that evolutionary psychology is true.

Mansfield’s meaning is vague when he stated that the evolutionary notion of nature denies “unchangeable nature” and “the permanent structure of things as nature.” His language resembles the assertion of Russell Kirk that conservatives who cherish “the permanent things in human existence” must see Darwinian science as a threat to their principles. Mansfield and Kirk seem to think that human nature is not a solid ground of moral norms unless it is eternally unchanging. Darwinian science sustains the idea that the nature of the human species is stable over long periods of evolutionary history but not eternal. Many conservatives would say that the eternal ground of human nature is God as the Creator.

What Mansfield says about evolution not recognizing “our better, higher nature” suggests that he would agree with the criticisms of evolutionary theory made a few years ago by Andrew Ferguson in the Weekly Standard. According to Ferguson, conservatives like Fukuyama and James Q. Wilson have made a big mistake in embracing Darwinian science, because they do not see the morally corrupting effects of the determinism and materialism that it promotes. To sustain the moral dignity of human nature, we need to affirm the existence of “autonomous selves” with a “free will” that cannot be explained by the scientific materialism of Darwinian biology.

Ferguson dismissed the evolutionary explanation of human nature as a “speculative theory” that is “untestable” and, thus, “unverifiable.” There can be no fossil record of human psychological traits inevolutionary history, and, therefore, the theories of the evolutionary psychologists are unproven conjectures. Proponents of “intelligent design theory”—such as Philip Johnson, Michael Behe, and William Dembski—have argued that Darwin’s whole theory of evolution by natural selection is an unproven dogma of scientific materialism that ignores the “irreducible complexity” in living things that points to an Intelligent Designer. Many conservatives have adopted this “intelligent design” position because they think it avoids the degrading materialism and atheism of Darwinian science.

This suggests at least five objections from conservatives against the possibility of a Darwinian conservatism of natural law rooted in human biology. The first is that Darwinian evolution weakens the natural ground of moral norms by denying an “unchangeable nature.” The second is that Darwinism subverts the moral dignity of human beings by promoting atheism. The third is that Darwinism denies moral freedom by promoting deterministic materialism. The fourth is that “intelligent design theory” has refuted Darwinism. A final objection is that a Darwinian view of evolved human nature opens the way to the use of biotechnology to change, or even abolish, human nature.

I will defend Darwinian conservatism against these objections. And I will use the biological account of natural sex differences as surveyed by Rhoads to illustrate my points.

The first objection is suggested by Mansfield. He is disturbed by the thought that if we accept Darwin’s theory of evolution, then the human species, like every other species, is not eternal but a contingent result of evolutionary history that can pass away; and that, therefore, the human good as relative to the desires of the human species is also contingent. But this should not disturb us unless we believe that the objective reality of the natural human good depends on its being an eternal good.

Even if species are not eternally fixed but have evolved from ancestral species, that does not make them any less real for as long as they endure. That human beings now exist and exist with the nature they have means that we can judge as good whatever conforms to their nature and as bad whatever does not. As Aristotle said in response to Plato, “the Idea of the Good will not be any more good because it is eternal, seeing that a white thing that lasts for a long time is not whiter than a white thing that lasts for a day.” Something good for us because it serves a natural human desire is no less good if our species survives for only a few hundred thousand years. If a huge meteorite were to collide with the earth tomorrow and kill us all, would not we still have to say it was good while it lasted?

That men and women have the natures that they do is the product of evolutionary history that will endure for as long as the human species endures. That these natural sex differences are not eternal does not make them any less real as persistent traits of the human species. Because the human species has evolved as a sexually reproducing species, with males and females having somewhat different propensities,the goodness of our lives will depend, in important respects, on our sexual identity as males or females. As Rhoads indicates, many women who believed that they were not naturally different from men are now deeply unhappy because their feminine desires for children and marriage have been frustrated. Similarly, many men who believed that they could live as sexually promiscuous loners with no enduring marital commitment are now deeply unhappy because they lack the stabilizing satisfaction of conjugal love. That what is naturally good for us depends to some degree on our biological nature as men or women with sexual, conjugal, and parental desires is true regardless of whether that biological nature is eternal or evolved.

Religious conservatives would say that our nature as men or women was created by God. And so the second objection to Darwinian natural law comes from religious conservatives who fear that Darwinian evolution is morally corrupting because it denies God’s creative power, promotes atheism, and, thus, denies God’s law for us as men and women, husbands and wives, parents and children.

Yet, the Darwinian view of life as having evolved by natural law is atheistic only if one assumes that God was unable or unwilling to execute His will through the laws of nature. I see no support for this position in the Bible. Theistic evolutionists such as Howard Van Till, Keith Ward, and John Haught have argued that the Bible presents the Creator as having fully gifted His Creation from the beginning with all of the formational powers necessary for evolving into the world we see today.

To be sure, there are militant Darwinian atheists, such as Richard Dawkins. But I see no reason to accept Dawkins’s and others’ claim that Darwinian science dictates atheism. In contrast to people like Dawkins, Charles Darwin insisted that ultimate questions of First Cause-questions about the origin of the universe and the origin of the laws of nature-left a big opening for God as Creator. As he said, “the mystery of the beginning of all things is insoluble by us.”

The fundamental idea of natural moral law is that it can be known by natural experience by all human beings regardless of whether they are religious believers or not. So it is that Rhoads can present the observable evidence for the natural biological differences between men and women, and we can see the natural moral implications of these differences. We can see, for example, that marriage is good for both men and women and for social order generally. Religious beliefs can reinforce our natural moral sense about sex differences and the importance of marriage. But even those without such religious beliefs can see how sex differences and marriage conform to our human biological nature as shaped in evolutionary history. And some religious conservatives (such as Leon Kass, for example) can see how a Darwinian explanation of natural sex differences confirms the Biblical view of human nature.

One expression of the special status that human beings have as created in God’s image is that they have a moral freedom that other animals do not have. As a third objection to Darwinian natural law, some religious believers warn that a Darwinian view of human nature promotes a materialistic determinism that denies this moral freedom because a Darwinian science assumes that everything human beings do must have a natural cause. According to this argument, if human behavior were as completely determined by the material laws of nature as animal behavior is, then human beings would not have “free will,” and we could not hold them morally responsible for their actions. A biological science of human nature cannot explain human morality if morality presupposes a human freedom from nature that sets human beings apart from the animal world.

In response to this argument, I would agree that if moral freedom required a “free will” understood as an uncaused cause—that is to say, will acting outside the causal laws of nature—then Darwinian science would deny moral freedom. But this notion of “free will” understood as an uncaused cause is contrary both to our common experience and to Biblical religion.

This idea of “free will” as uncaused cause is a Gnostic idea that treats the human will as an unconditioned, self-determining, transcendental power beyond the natural world. This Gnostic idea came into modern moral philosophy through the influence of Immanuel Kant.

Such a notion contradicts Biblical religion because the only uncaused cause in the Bible is God. I agree with Jonathan Edwards, who argued that whatever comes into existence must have a cause. Only what is self-existent from eternity-God-could be uncaused or self-determined. In contrast to the nonsensical notion of “free will,” the commonsense notion of human freedom means the power to act as one chooses, regardless of the cause of the choice. Edwards was arguing against the Arminian notion of moral freedom as the absolute self-determination of will. That same Arminian notion of “free will” as separated from natural causality was adopted by Kant.

A Darwinian science of the moral sense would support this commonsensical notion of moral freedom as described by Edwards. A biological explanation of human nature does not deny human freedom if we define that freedom as the capacity for deliberation and choice based on one’s own desires. We hold people responsible for their actions when they act voluntarily and deliberately. They act voluntarily when they act knowingly and without external force to satisfy their desires. They act with deliberate choice when, having weighed one desire against another in the light of past experience and future expectations, they choose that course of action likely to satisfy their desires harmoniously over a complete life.

This is Darwin’s understanding of moral responsibility. Because he believes that “every action whatever is the effect of a motive,” he doubts the existence of “free will” understood as uncaused cause. However, he believes that we are still morally responsible for our actions because of our uniquely human capacity for reflecting on our motives and circumstances and acting in the light of those reflections. He writes: “A moral being is one who is capable of reflecting on his past actions and their motives—of approving of some and disapproving of others; and the fact that man is the one being who certainly deserves this designation is the greatest of all distinctions between him and the lower animals.”

As sexual animals, our nature is deeply formed by our natural identity as male or female. Consequently, we are not utterly self-determining beings because our sexual identity influences our choices in life.The mistake of the radical gender feminists is assuming that in a gender-neutral society we would be able to disregard our sexual identity and act freely as androgynous beings. The evidence surveyed by Rhoads reminds us of how we cannot escape the particular sexual identities that nature has given us. We do not have the freedom of disembodied spirits. But we do have the freedom to deliberate about how best to satisfy the natural desires that we have as male or female creatures.

As a fourth objection to Darwinian natural law, some conservatives claim that Darwinian science has been refuted by “intelligent design theory.” Both the strength and the weakness of “intelligent design theory” as an intellectual movement come from the rhetorical technique of negative argumentation from ignorance. The strength of such rhetoric comes from exposing the ignorance of one’s opponents. The weakness comes from one’s failure to offer any positive explanation of one’s own. This creates a rhetorical situation in which the winner of the debate is whichever side can put the other on the defensive.

If you have ever attended one of the public debates on intelligent design theory versus Darwinian biology, you have heard each side trying to put the other side on the defensive by assuming a purely negative stance. The proponents of intelligent design appear to win when they ask their Darwinian opponents to explain the exact causal pathways by which natural selection formed the living mechanisms that show apparent design. The Darwinians appear to win when they ask the proponents of intelligent design to explain the exact causal pathways by which the disembodied intelligent designer created those same living mechanisms.

Jonathan Wells understands this rhetorical strategy very well. In his book Icons of Evolution, Wells shrewdly employs a purely negative approach-attacking weaknesses in Darwinian theory while refusing to defend intelligent design in any positive way. He encourages the reader to assume that if Darwinian evolution has not been absolutely demonstrated to be true, then the idea of creation by an intelligent designer wins by default as the only reasonable alternative. But in doing this, Wells demands standards of proof for Darwinian biology that are unreasonably high. After all, Wells himself could never satisfy those standards if he had to show the exact causal mechanisms by which a disembodied intelligence shapes natural objects in the living world.

Darwin acknowledged that there were many serious objections to his theory. In his book The Origin of Species, he devoted more than one-third of his chapters to considering the “difficulties” for his theory, and these are the same difficulties that are emphasized by the intelligent design critics. Darwin admitted that some of the objections “are so serious that to this day I can hardly reflect on them without being in some degree staggered.” And yet, he answered those objections and insisted that his theory would emerge as highly “probable” if one considered the “facts and arguments” in its favor.

Evolutionary biology is not a mathematical science that allows absolute demonstration. Evolutionary biology permits only probable reasoning that is more or less persuasive. Evolutionary biology has all of the difficulties that come from being a historical science concerned with unique events in the past that cannot easily be directly observed or experimentally replicated in the present. The record of the past-such as the geological record of fossils-is incomplete, and, therefore, Darwin’s theory of evolutionary history cannot be proven conclusively. Proponents of intelligent design theory can exploit this limitation by demanding complete historical and experimental evidence for Darwin’s theory. They can then conclude that the theory is unsupported by the evidence whenever the evidence is incomplete, as it always will be. But this rhetorical strategy is unreasonable because it denigrates the impressive evidence for Darwin’s theory and because it demands a standard of proof that the intelligent design proponents themselves have not met in showing exactly how an omnipotent, disembodied intelligence works in the world.

There is an easier way around the objection to Darwinian natural law coming from intelligent design theory. Although the proponents of intelligent design object to evolutionary explanations of the distant causes of human biological nature, they do not seem to object to biological explanations based on more proximate causes. To find common ground among conservatives for accepting a biologically rooted natural law, we could set aside the arguments from evolutionary biology and rely only on arguments from behavioral biology. Even if we cannot agree on the evolutionary causes of human nature, we might still agree on the proximate causes of human behavioral biology. Evolutionary causes are difficult to judge because they often are not directly observable, and we have to infer evolutionary history from indirect evidence (such as the fossil record). In contrast, proximate causes are often open to direct observation. For example, we can measure fluctuations in hormonal levels and correlate that with behavioral changes.

In surveying the evidence for natural sex differences, Rhoads relies on both the proximate causes of behavioral biology and the distant causes of evolutionary biology. Even if some conservatives reject the latter, they might still accept the former. In appealing to behavioral biology, Rhoads draws evidence from endocrinology, developmental biology, genetics, neuroscience, and animal behavior. For the most immediate causes, he relies on opinion surveys or anecdotal reports from men and women about their desires and emotions. He also uses cross-cultural anthropological studies of sex differences. Even conservatives who object to evolutionary biology could accept Rhoads’s account of behavioral biology as supporting his conclusion for biological sex differences.

For example, Rhoads refers to studies showing that the higher average levels of testosterone among men as compared with women create sex differences in their athletic interests and abilities. He then adds that “evolutionists believe these hormonal differences are explained by natural selection.” Conservatives who accept intelligent design theory will say that what “evolutionists believe” is wrong. But these same conservatives can accept the hormonal evidence for natural sex differences. So this kind of evidence from behavioral biology could sustain a biologically grounded natural law even for those conservatives who are skeptical about evolution.

Yet, even if we set aside evolutionary theory and rely only on behavioral biology, any biologically grounded natural law will be unacceptable to many conservatives who worry that biological science without religious belief cannot sustain traditional morality. For these conservatives, the debate over biotechnology manifests the problem.

Rhoads hints at the problem in one sentence, but he does not face up to it. Declaring that the sex differences between men and women are natural because they are biological, Rhoads observes: “They won’t disappear unless we tinker with our fundamental biological natures.” To which some radical feminists might respond, So let’s start tinkering!

Shulamith Firestone is a radical feminist who would agree with Rhoads that the differences between men and women are biologically natural. She argues that sexual inequality is ultimately rooted in the biological nature of the reproductive process that ties women to reproduction and parenting in a manner that supports a sexual division of labor that favors the rule of men over women. She rejects as too shallow the gender feminist claim that sex differences are merely “social constructions” that can be changed by social reforms. The true feminist revolution, she insists, will require the use of technology to conquer nature-including the biological nature of reproduction—so that the natural differences between men and women are abolished. So, for example, the use of biotechnology to turn reproduction into a purely artificial process (including artificial wombs) would finally liberate women from enslavement to their reproductive functions.

Rhoads makes much of the hormonal differences between men and women that cause differences in men’s and women’s abilities and interests. The higher levels of testosterone among men, for example, elevate their athletic abilities and interests above those of women. But, as we know, athletes can now inject themselves with testosterone and anabolic steroids (chemicals related to testosterone) to enhance their athletic performance. So, why not use such biotechnological pharmacology to turn women into men or, perhaps, to turn both women and men into androgynous beings? In the 1970s and 1980s, many female athletes in East Germany were artificially injected with testosterone to the point that they took on many masculine traits. Perhaps the Department of Education should interpret Title IX as requiring that all publicly funded schools must provide performance-enhancing drugs to female athletes so that they can compete equally with male athletes. Furthermore, those people who have undergone complete sex changes show us how far we have already gone in gaining technological control over the biological nature of sexual identity. Rhoads never explains what is wrong with Firestone’s argument that recognizing the biological roots of sex differences invites us to look for biotechnological ways to abolish those differences.

Many religious conservatives would answer Firestone by warning that to try to change human nature through biotechnology is wrong because it is playing God. For these conservatives, we cannot ground moral law on human biological nature unless we can see that nature as sanctioned by a supernatural Creator. Without such religious belief, they worry, a biological understanding of human nature puts no moral limits on our power to use our biological knowledge for altering, if not abolishing, human nature through biotechnology.

Carson Holloway has stated this objection very well. Darwinian science does not support a cosmic teleology. If we accept the Darwinian theory that all life has arisen in evolutionary history through natural selection working on random heritable variations to adapt species for survival and reproduction, then the living world was not designed by a cosmic intelligence to serve some cosmic purpose. Even the human species is a product of evolutionary contingency because the emergence of the human species is a result of an evolutionary history that could have turned out differently. There is an immanent teleology in the sense that once the human species exists, human beings will strive purposefully to satisfy the desires inherent in their nature. But there is no cosmic teleology that would allow us to judge human purposes as fulfilling some cosmic purposes written into the universe. If there is no such cosmic teleology that sanctions the goodness of human nature, Holloway objects, then there is no reason why human beings should not use biotechnology to change, or even abolish, their human nature if they find that nature unsatisfactory. In contrast, Holloway argues, religious believers who think that human beings were created by God in His Image will see humanity as having supreme worth according to God’s cosmic purposes, and they will see the biotechnological transformation of human nature as a violation of God’s law. Without such religious beliefs, Holloway worries, there would be no good reason to stop biotechnology from creating a “posthuman future.”

Part of that “posthumanity” might be the biotechnological abolition of natural sex differences. We might be persuaded by radical feminists like Firestone that it would be a great liberation to transform human beings into androgynous animals because this would eliminate the biological differences between the sexes that impede human harmony and cooperation. The only good reason to reject such a proposal, Holloway would suggest, is the religious objection that because God created human beings as male and female to serve his cosmic plan, it would violate divine law for us to abolish natural sex differences. Without such a cosmic teleology founded on religious belief, we would have no persuasive objection on the grounds of secular reasoning to Firestone’s proposal.

I agree that religious belief can be important in reinforcing traditional morality. That is why conservatives generally support religious belief. But I do not agree that the natural moral sense requires religious belief. Any appeal to God as the supernatural source of morality creates more controversy than it resolves. First, we would have to agree on the existence and benevolence of God, but that raises issues that are even more controversial than morality. Second, even if we could agree on God’s existence and benevolence, we would have to communicate with him to determine his will, but human beings have never found any authoritative way to choose between contradictory claims to divine communication. Conservatives like Holloway commonly appeal to the Judeo-Christian tradition of the Bible. But, of course, there are deep disputes between Jews, Catholic Christians, Protestant Christians, and Muslims over the Biblical texts.

Conservatives like Holloway might argue that all we need for moral purposes is the Old Testament teaching of God as Creator who created human beings in His Image. Like many religious conservatives, Holloway assumes that Biblical religion promotes the idea of the equal moral dignity of all human beings as human beings. But that is not at all clear. The Hebrew Bible teaches that the Jews are the chosen people of God, and they are often commanded by God to extinguish their enemies, even when this means killing innocent women and children (see, for example, Numbers 31:1-19; Joshua 6:17-24; 1 Samuel 15:3). But then the New Testament suggests that the Jews will be condemned by God if they reject salvation through Jesus, and this supports the Christian tradition of anti-Semitism. The anti-Semitism of Martin Luther was so brutal that it could be used by the Nazis in Germany to justify their attack on the Jews. The Book of Revelation predicts that earthly history will end with the forces of the Christian Church annihilating the forces of Satan. Both the Old Testament and the New Testament sanction slavery (see, for example, Ephesians 6:5-9). In fact, an important part of the proslavery arguments in the American South before the Civil War was that slavery was based on the law of God as conveyed in the Bible. The modern assumption that the Bible teaches the universal moral equality of all human beings has arisen largely from the strained interpretation of the Biblical texts by political philosophers like John Locke.

I am not persuaded that the Imago Dei doctrine has the moral clarity and specificity to resolve our debates over biotechnology. After all, many Jewish and Christian theologians have argued that the Hebrew Bible would sanction biotechnology as an expression of human mastery. Because human beings have been created in God’s image, and because God is the Creator, then human beings must share somehow in God’s creativity. The Bible is explicit in declaring that when God made man in his image, this was to include “dominion” or “mastery” over all the earth, including all animals. In the phrase of Christian theologian Philip Hefner, human beings are “created cocreators.” As “created,” we are creatures, and we cannot create as God-who can create ex nihilo, “from nothing”-creates. But as “cocreators,” we can contribute to changes in creation. Christian theologian Ronald Cole-Turner concludes that “genetic engineering opens new possibilities for the future of God’s creative work.”

Presumably, religious conservatives like Holloway would say that these theologians have misinterpreted the Bible. But how do we escape such disagreements over the interpretation of God’s message? And is this not particularly a problem with biotechnology, because the Bible says nothing about the specific techniques of biotechnology?

It is not even clear that the Bible teaches us that our given human nature is good and should never be changed. After all, if one accepts the doctrine of original sin, the nature that we have is not the original human nature created by God but the depraved human nature that we inherit as a consequence of the sinful choices made by Adam and Eve. Indeed, it seems that some of the natural differences between men and women-such as the pain of childbirth for women and the dominance of men over women-arose only as a punishment for this original sin (Genesis 3:16). Firestone argues that biotechnology could be used to undo the curse inherited from Adam and Eve and restore the earthly Garden of Eden. Holloway would probably respond by insisting that it would violate God’s law for human beings to attempt to redeem themselves from Adam’s curse. But, again, this brings up the problem that religious believers cannot agree on interpreting God’s will as it applies to the technological conquest of nature.

So how, then, would a Darwinian conservatism handle the possibility of a biotechnological transformation of human nature? My main point would be that the power of biotechnology for changing human nature has been exaggerated. The most fervent advocates of biotechnology welcome the prospect of using it to transform our nature to make us superhuman. The most fervent critics of biotechnology warn us that its power for transforming our nature will seduce us into a Faustian bargain that will dehumanize us. Both sides agree that biotechnology is leading us to a “posthuman future.” But this assumption is false. It ignores how evolution has shaped the adaptive complexity of our human nature-our bodies, our brains, and our desires-in ways that resist technological manipulation. A Darwinian view of human nature reveals the limits of biotechnology so that we can reject both the redemptive hopes of its advocates and the apocalyptic fears of its critics.

Biotechnology will be limited both in its technical means and in its moral ends. It will be limited in its technical means because complex behavioral traits are rooted in the intricate interplay of many genes that interact with developmental contingencies and unique life histories to form brains that respond flexibly to changing circumstances. Consequently, precise technological manipulation of human nature to enhance desirable traits while avoiding undesirable side effects will be very difficult, if not impossible. Biotechnology will also be limited in its moral end, because the motivation for biotechnological manipulations will come from the same natural desires that have always characterized human nature.

To illustrate these points, consider, again, the possibility of using the biotechnological manipulation of testosterone to make women the same as men. The difference in testosterone between men and women is a matter of degree. Women have testosterone as well as men, but women, on average, have lower levels than men. There is great individual variability-there are high-testosterone women just as there are low-testosterone men. The sex difference arises from the differences in the normal levels for men and women. Actually, of course, sexual identity depends on more than just hormonal levels, which is why people who attempt total sex changes discover that this is frustrating in its complexity.

Before the fall of the Berlin Wall, the East German government enhanced the performance of female athletes by injecting them with testosterone so that their levels of testosterone were seventy times higher than is normal for women. This did improve their athletic performances but only with severely harmful side effects-such as severe acne, spreading growth of pubic hair, uncontrolled libido, tumors, internal bleeding, deformed babies, and deep depression. Christiane Knacke-Sommer won a bronze medal in swimming at the 1980 Moscow Olympics. But later she testified against the officials who had forced her to take testosterone pills while telling her that they were only vitamins. At the end of her testimony, she pointed at the defendants and shouted, “They destroyed my body and my mind!” She then threw her Olympic medal on the floor.

This case illustrates the limits on the technical means of human biotechnology. Any biological manipulation to make major changes in the human body or mind-such as making female athletes perform just like men-is likely to have severely harmful side effects because it will upset the natural balance in the human organism as adapted by natural selection.

This issue also illustrates the limits on the moral ends of biotechnology. High athletic performance satisfies human desires for recognized excellence and physical achievement. But with the possible exception of people with serious mental disorders, human beings desire to maintain their sexual identity as male or female. Of course, we can make mistakes and desire something that turns out to be undesirable, as happens with athletes who take performance-enhancing drugs and later regret some of the consequences. But we would not deliberately, with full understanding of what we were doing, desire to manipulate our bodies and minds through biotechnology if this meant that we would lose our identity in the process. Some women might want to be more manly in their traits, just as some men might want to be more womanly in their traits. And such desires might motivate us to use biotechnological manipulation to modulate our sexual identities. But normal men and women would not choose to obliterate their identity as men and women for the sake of androgynous gender neutrality because to do so would be psychic suicide.

The potential harm in trying to eliminate natural sex differences should be evident in the famous case of David Reimer. David was originally born in 1965 in Winnipeg, Canada, as Brace Reimer, with an identical twin brother Brian. When he was eight months old, a doctor botched his circumcision so badly that his penis was cut off. His parents were referred to Dr. John Money of Johns Hopkins University, who was one of the world’s leading experts on gender identity. He believed that gender identity was flexible enough that a boy could be turned into a girl under the right conditions. To test his theory, he advised Bruce’s parents to raise him as a girl-Brenda. The new girl was feminized through sexual surgery, estrogen supplements, and a social upbringing as a girl. The case was widely reported by radical feminists as proof that sex differences were not fixed by nature because here was a case of a boy turned into a girl, and the contrast with his identical twin seemed to provide the perfect experiment.

Only later did it become known that this sex reassignment was not a success. As a child, Brenda tore off her dresses. She refused to play with dolls. She complained that she felt like a boy. But Dr. Money had advised her parents never to tell her what had happened. When Brenda was fourteen, she was finally told the truth. Later, she said, “Suddenly it all made sense why I felt the way I did. I wasn’t some sort of weirdo. I wasn’t crazy.” She went back to her original male sex, taking the name David. Surgery was required to remove the breasts that had grown from estrogen therapy and then to create an artificial penis and testicles. Injections of testosterone masculinized his body. Eventually, he married a woman and seemed happy for a few years. But he never fully recovered from his experience, and he was angry at what had been done to him. John Colapinto wrote a book about David’s story as an illustration of the great harm that can come from denying the nature of sex differences. In 2004, David was thirty-eight years old. On May 5, he got a shotgun, sawed off the barrel, and ended his painful life.