Undetermined: there is danger in assuming that genes explain all.

THE delineation of the double-helix structure of DNA by Watson and Crick in 1953 will almost surely rank as one of the most epochal scientific discoveries in human history. Following rapidly upon the synthesis of Darwinian evolution with Mendelian genetics in the 1930s and '40s, it enabled a research program that now seeks to explain a vast array of physical phenomena, from the functioning of individual organisms to the development of species over geological time. This success has led some science popularizers to believe that we have found a new Rosetta Stone enabling us to understand many of the mysteries of human existence. But if translated into public policy, their belief would likely have disastrous results. In the coming decades, it will be important for conservatives to walk a fine line: on one hand, to resist such hubris; on the other, not to throw the baby out with the bathwater by denying valid biological science.

Driven by the genetic revolution, biology has displaced physics as the world's most important and exciting science. A substantial majority of all U.S. academic-research spending in science and engineering is now in life sciences. More than twice as many of the developed world's most widely cited scientific research papers are in the life sciences as are in physics and chemistry combined. Successful new scientific paradigms change how we see the world, and therefore exert intellectual influence well outside of the technical specialties that produced them. The more fundamental the paradigm, the wider and deeper are these radiating influences. In the case of modern biology, they are profound. Proceeding from the sociobiology movement of the 1970s, some biologists have sought to explain all individual behavior and social organization as the predictable result of genes-plus-environment. The reigning presumption of academic America is that over time this movement will sweep all before it.

This perspective inevitably trickles down into mainstream opinion. To choose just a few illustrative examples, within the past few months both Time and The New York Times Magazine have had cover stories on the evolutionary roots of morality; Time has had a second cover story on the biological basis of romance; Newsweek has had one article on the genetic explanation of psychological resilience and another arguing that varying incidences of disease-causing pathogens explain the degree to which different countries' policies are individualist or collectivist; NBC News has broadcast a story on the genetic basis for smoking addiction; ABC has had a story on the evolutionary origins of the incest taboo; and CBS has run a story titled "Eureka: Happiness Gene Found." Mass media are inundated with this biology-explains-all ideology.

OLD THOUGHTS, NEW ERRORS

Now, the idea that the vast majority of people share a set of stable, inherent characteristics--that is, the idea that there is such a thing as human nature--is not new. Nor are the subsidiary ideas that individuals have somewhat varying inborn natures; that this variation is partially heritable; and that individuals who share a lineage will demonstrate common traits and tendencies. All of these beliefs are at least several thousand years old, and probably predate written records.

What's new is that--because we believe that we have uncovered at least a component of the physical manifestation of human nature, in the form of the genome--many now believe that we can operationalize these old ideas: that we can explain the causes of the behaviors of individuals and groups sufficiently to predict these behaviors scientifically. Those who believe this, believe that we can remove the mind-body problem from the purview of philosophy by reducing the mind to a scientifically explained physical phenomenon. When pushed, such theorists will generally admit that we cannot yet do much of this, but will then state confidently that we "are starting to understand" or "are on the verge of explaining" various human behaviors.

Media outlets will often speak loosely of things such as a "happiness gene," a "gay gene," or a "smart gene." The state-ofthe-art method for finding such a link is something called a "genome-wide association study" (GWAS). In a GWAS, scientists use blood or saliva samples to sequence the DNA for a group of several thousand people who exhibit a trait or behavior of interest (the "case group"), and for a second group of several thousand who do not exhibit the trait or behavior (the "control group"). Scientists then look for genetic differences between the two groups. In cases where a single malfunctioning gene creates, for example, a catastrophic disease that overwhelms other genetic and environmental factors, a GWAS can quickly pinpoint the culprit. Sometimes, however, the behavior or trait is caused by several interacting genes--so that, for example, Gene 1 has some effect only if Gene 2 has a special structure. This is called "epistatic interaction," and can involve a large number of genes. Epistatic interactions make genetic effects harder to identify. Scientists deal with this problem and others by creating larger and larger case and control groups. The scaling up of such studies is among the most exciting frontiers in genetics. It is essentially an engineering problem, and money poured into solving it will likely improve human health through genetic screening and, ultimately, therapies.

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Seeing this momentum, it is natural to assume that eventually we will have explained all human behavior, not just diseases caused by one or a small number of interacting genes. But the GWAS technique hits structural limits when applied to conditions that involve epistatic interactions among lots of genes. Mental activity is now widely believed by scientists to depend on many genes (though mental illnesses such as schizophrenia or bipolar disorder may turn out to be partial exceptions). A person has about 20,000 genes, of which more than 5,000 are believed to play some role in regulating brain function. Consider a simplified case in which some personality characteristic--aggressiveness, for example--is regulated by 100 genes, each of which can have two possible states ("on" or "off"). The combinatorial math is daunting: There are more than a trillion trillion possible combinations of these gene states. Thus we could sequence the DNA of all 6.7 billion human beings and still not know which genes are responsible for aggressiveness.

A second limitation of a GWAS is that it detects association rather than causation. Suppose we found that a case group of persons suffering from a disease had a greater incidence of some gene than did a control group, but that we failed to notice that the case group was disproportionately of Chinese ancestry. Culturally transmitted behaviors in the case group might be responsible for the disease, even if these behaviors had nothing to do with the gene in question. That is, the gene could be nothing more than a marker for Chinese ancestry, and hence for participation in behaviors that cause the disease. Geneticists call this problem "stratification," and deal with it by carefully matching individuals in the case and control groups to ensure that the groups really are comparable. The problem is that these stratification effects can be fiendishly subtle. No matter how carefully we match cases with controls, there can always be some unobserved environmental factor correlated with, but not caused by, a genetic difference between groups, and this environmental factor might be what is actually causing the disease.

Further, to think in terms of genes is to abstract away from a biochemical reality that is far more complex. On one hand, a gene is not an atomic entity, but a sophisticated machine with many components. Much as in the progress of particle physics over the past century, we keep discovering components-within-components of the genetic mechanism that are relevant to physical and mental outcomes, and it's entirely plausible that we will eventually get all the way down to subatomic quantum effects as drivers of behavior. On the other hand, as we move away from the genome itself, we see that other dimly understood biochemical processes have a large impact on how the information contained in the gene gets expressed as an observable human characteristic. And all of this is before we consider interactions of the human organism as a whole with those factors that we typically term "environmental," ranging from nutrition and exposure to pathogens to parenting styles and childhood experiences.

CORRELATION IS NOT CAUSALITY

So how is a GWAS showing an association between Gene X and aggressiveness different from a social-science study showing a correlation between watching lots of violent TV and aggressiveness? Mathematically, it's not. In both cases we start by measuring aggressiveness for each person. We then compile for each person a list of data providing information on potential causes of aggressiveness: in one case genomic information, and in the other, sociological observations on childhood experiences, school quality, and so on. In the first case we observe that aggressive people have a higher incidence of Gene X; in the second that they watch a lot of violent TV. The reliability of GWAS studies is thus subject to the same limitations that we think of in connection with sociology or economics (as opposed to, say, chemistry). The only way around this--the only way to attain the precision of chemistry --would be actually to show the chain of biochemical processes by which a set of named genes creates the observable brain functions collectively defined as "aggressiveness." Of course, if we could do that, we would have no need for a GWAS study.

The claims of causality that arise from such studies should accordingly be treated with the appropriately intense skepticism that we apply to sociological or econometric studies. In the middle of the 20th century, Friedrich Hayek and the libertarians he inspired faced those who asserted that that an economy could be successfully planned. The libertarian position was not that such planning could be proved impossible in theory, but that we lacked sufficient information and processing power to accomplish it. The world of economic interaction is so complex that it overwhelms our ability to render it predictable; hence the need for markets to set prices. This is the same analytical problem we face when trying to predict a mental state that depends upon a large number of genes. It is unclear whether we will ever understand how this complicated machinery and its interactions with the environment come together to create characteristics of mind. It is certain, however, that we do not have such an understanding now, and that we won't know such a project is achievable until we achieve it.

Consider a prominent example of the debate over genetic causality: the assertion that there is a genetic basis for IQ differences between racial groups. Because it is both so consequential and so fraught with emotion, this claim has been subject to an almost unique degree of critical scrutiny, descending into the kind of irresolvable debate that we see in economics and the social sciences.

Let's start with some facts. There are sustained, statistically significant differences in IQ-test performance between self-identified racial groups in the U.S., and these self-identified racial groups also have statistically significant differences in genetic content. But those who assert that these genetic differences cause the difference in test scores have never been able to demonstrate a physical pathway from genes to IQ. In the absence of such a demonstration, they have had instead to rely on those old standbys, twin and adoption studies. (The logic here is that these studies can control for either genetics or the environment. Identical twins have identical DNA. By looking at cases of adoption, meanwhile, researchers can study children whose genetic background differs from that of the families in which they are raised.) The most famous and rigorous such study was the Minnesota Transracial Adoption Study of families in which high-IQ white parents adopted black, white, or mixed-race children. In theory, studying these subjects should have allowed us to isolate the influence of genes on intelligence, by measuring the IQs of children in each group after they had been raised in approximately equal environments. But it turned out that the environments were not even close to equal. The black children had been adopted at later ages than the white children, and this can plausibly be associated with differing scores on IQ tests.

The Minnesota study provides a good illustration of why it is so difficult to separate genetic from environmental effects: No such experiment in a non-totalitarian society is sufficiently controlled to support reasonable inferences. When we use these methods to try to understand the causes of IQ differences between groups, we are like cavemen trying to figure out how a computer works by poking at it with sharpened sticks. This, not political correctness, is why the American Psychological Association's consensus on the matter of race and IQ is that, "at present, this question has no scientific answer."

When we carefully consider assertions of a genetic basis for other mental or social phenomena, this pattern emerges time and again. The explanation sounds plausible--it might be true--but we can't be sure. Is the almost-universal human religious impulse a byproduct of evolution? Perhaps. Can altruism be explained fully by genetic competition? Could be. Does homosexuality have a genetic cause? It's possible.

SOUND THE WARNING

The fallacy of what might be called "geneticism" is particularly tempting to conservatives, because it appears to provide scientific support for the idea of an innate human nature--an idea that has long been assaulted from the left. But this temptation should be resisted. If the pretense to scientific knowledge is always dangerous, it is doubly so when wedded to state power, because it leads to pseudo-rational interventions that unduly extend authority and restrict freedom. That the linkage of race and IQ is provocative to contemporary audiences is not surprising: It is almost a direct restatement, in the language of genetics, of the key premise of Social Darwinism. That prior attempt to apply beliefs about human nature to public policy should be a cautionary tale for our era.

Just as Newtonian physics formed part of the backdrop for the thought of the Founders, Darwinian biology--from its beginnings, even before being synthesized with genetic theory--has found expression in both descriptions of physical evolution and conceptions of human society as similarly evolving. In the decades after the publication of On the Origin of Species, evolution became the dominant scientific metaphor for understanding human society. Woodrow Wilson was clear about this when he said in The New Freedom (1913):

   Now, it came to me ... that the Constitution of the United States
   had been made under the dominion of the Newtonian Theory ...

   Politics in [the Founders'] thought was a variety of mechanics. The
   Constitution was founded on the law of gravitation. The government
   was to exist and move by virtue of the efficacy of "checks and
   balances."

   The trouble with the theory is that government is not a machine,
   but a living thing. It falls, not under the theory of the universe,
   but under the theory of organic life. It is accountable to Darwin,
   not to Newton. It is modified by its environment, necessitated by
   its tasks, shaped to its functions by the sheer pressure of
   life.... There will be the family in a great building whose noble
   architecture will at last be disclosed, where men can live as a
   single community, cooperative as in a perfected, co-ordinated
   beehive.

Many thinkers at that time believed that Darwinian evolution represented not just a metaphor, but a physical explanation of the material superiority of European civilization. The application of evolutionary ideas supported the eugenics movement in the U.S. and Europe, in which policymakers gave natural selection a helping hand by encouraging differential breeding rates for "fit" and "unfit" persons.

This idea was the basis of Oliver Wendell Holmes Jr.'s Supreme Court opinion upholding the right of the Commonwealth of Virginia to sterilize the feeble-minded, which ends with the immortal statement that "three generations of imbeciles are enough." Let's be clear about the results of this decision. Aspecific 18-year-old girl named Carrie Buck, who had been accused of no crime, was placed on a table, whereupon an agent of the state sliced open her abdomen and cut her Fallopian tubes against her will. She lived from that moment until her death with no chance of having children. All of this was done because Oliver Wendell Holmes Jr. was pretty sure that her children would not have been smart enough. The ironic denouement is that, just prior to this operation, Carrie Buck had actually had a daughter--whose subsequent performance in school was average at worst and often better.

This was not an aberrant case; over 60,000 Americans were forcibly sterilized in the 20th century. The Laughlin Model Law, which was the basis for most state statutes that regularized this practice, chillingly permitted the forcible sterilization of any "probable potential parent of socially inadequate offspring," and provided tactical inspiration for relevant statutes in Nazi Germany.

It was, in fact, the conflagration of the Holocaust that made human eugenics a more or less forbidden research topic for decades. But this halt has proved temporary. As the Holocaust passes from living memory, and biology makes enormous advances, the human inclination to intellectual vanity is reasserting itself. This seems almost inevitable. The sense of seeing beneath the surface of things, provided by the greatest scientific insights, is intoxicating. Genetic maximalists are just a modern version of the Pythagorean cultists or the Newton-inspired Enlightenment philosophes.

Despite their confidence in predicting future discoveries, however, our ignorance about humanity runs deep, and the complexities of mind and society continue to escape reduction to scientific explanation. This ignorance is one of the most powerful arguments for free-market economics, subsidiarity, and many of the other elements of the conservative worldview. Science may someday allow us to predict human behavior comprehensively and reliably, so that we can live in Woodrow Wilson's "perfected, co-ordinated beehive." Until then, however, we need to keep stumbling forward in freedom as best we can.