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Don’t Worry About the Human Gene Pool

Modern medicine may or may not be changing the evolutionary process, but we shouldn’t care.

By Michael White


(Photo: geneticdesigns/Flickr)

Should we worry about the future of the human gene pool? This question may sound like a throwback, something from the heyday of eugenics in the first half of the 20th century, when people dressed up their social prejudices as science and committed a variety of injustices and atrocities in the name of genetic purity. Today, eugenics is justifiably seen as disreputable, and concerns about our species’ genetic fitness are no longer common.

So it is surprising to read a recent warning by a leading geneticist who says that the human gene pool may be in trouble. Writing in a major genetics journal, Indiana University biologist Michael Lynch makes an argument that sounds much like the claims of eugenicists a century ago: Because modern medicine has become so effective at helping people survive and have children, it has reduced the ability of natural selection to remove harmful mutations from the human population. If nothing changes, we can expect a “genetic deterioration in the baseline human condition” over the coming generations.

Every person alive today is the beneficiary of this brutal process, a descendant of a lineage of evolutionary winners going back to the very first life on Earth.

This is obviously a highly charged claim, especially given how this type of argument has been used in the past. But Lynch, an influential geneticist who has a reputation for being provocative, isn’t trying to revive the racist eugenics of the last century. He doesn’t make the discredited claim, often made by advocates of eugenics, that certain races, ethnic groups, or socially disadvantaged classes of people are genetically inferior. He does, however, identify the uncomfortable place where our biology and our ethics come into conflict.

The problem starts with an important biological truth: Our genes are largely the product of natural selection. In other words, we, as a species, are who we are because of what happened in our evolutionary past: Individuals with less fit genes were more likely to die without leaving offspring than those with more optimal genes. Every person alive today is the beneficiary of this brutal process, a descendant of a lineage of evolutionary winners going back to the very first life on Earth.

As Lynch points out, however, natural selection isn’t just ancient history — it also plays an important, ongoing role in the maintenance of our genes. Genes are not stable things: New mutations inevitably arise in each generation — each of us is born, on average, with scores of new mutations. Most are harmless, but some of them do damage. Without natural selection acting to remove these mutations from the gene pool, they will accumulate over generations and gradually erode our species’ genes, leading to a deterioration in our physical and mental traits.

While natural selection clearly still operates when it comes to very damaging mutations, such as those that cause severe disease or are incompatible with life, Lynch worries about more common mutations, ones that are only mildly damaging. He argues that “the myriad of clinical procedures for mitigating the consequences of bad genes … can only result in the relaxation of natural selection against a broad class of deleterious mutations.” As a result, these mutations will accumulate in the human population, leading to a general decline.

This idea of genetic decline isn’t merely hypothetical; it’s something that has been studied with differentorganisms in the lab — though the relevance of these studies to human populations is debatable. Researchers, however, have now collected a great deal of data on human mutations rates, and Lynch uses this data to make some estimates of the scope of the problem. He finds that, in each generation, we would see “a 1% or so decline in the baseline performance of physical and mental attributes” in societies where natural selection was almost completely eliminated by modern medicine and public-health programs. This is where our biology and our ethics enter conflict: As we use modern technology to help as many people as we can, regardless of their DNA, we also may be undermining the genetic future of our species.

Is Lynch right? Should we be worried about the human gene pool?

It is misguided to sacrifice the well-being of people today on the slim chance that we might positively affect the human gene pool five or 10 generations from now.

Probably not — for both biological and ethical reasons. The most important biological reason is that, whether we like or not, natural selection still undoubtedly operates on our species. Take our most distinctive trait, our mental capacity. Lynch worries that, because many genes contribute to the functioning of our brains, our intellect is particularly vulnerable to the accumulation of mutations. But as other researchers have noted, “intelligence is strongly associated with evolutionary fitness, even in current societies.” Multiple studies, for example, have found an inverse relationship between intelligence and premature death, particularly in men. And if we’re truly concerned about the intellectual abilities of our population in general, there is strong evidence that genes aren’t the main problem. As Lynch acknowledges, there are enormous social and environmental factors that prevent millions of people from developing their full mental potential.

While it’s tempting to witness, as Lynch puts it, “the miracles of molecular biology and modern medicine” and conclude that we have almost completely transcended the process of natural selection, the vast bulk of our medical technologies don’t actually affect natural selection very much, because we use them to treat people who are well past their reproductive years. Certainly some aspects of natural selection have been greatly moderated by medical advances, but why should we care? Childhood deaths due to infectious diseases have fortunately declined dramatically over the past century, and thus the strength of natural selection on immune system genes has surely been reduced. But if we can successfully prevent or treat these diseases with medical technology and public-health tools, then mutations that might increase our susceptibility to these diseases are no longer very relevant to human fitness.

More importantly, we should ask ourselves, do we have any ethical obligation to care about the genetics of our species over the next several centuries, especially if it comes at the expense of giving the best care we can to people alive today? Evolutionary change is inevitable, and we have virtually no ability to accurately predict or control it. It is thus misguided to sacrifice the well-being of people today on the slim chance that we might positively affect the human gene pool five or 10 generations from now. If our goal is to make life better for future generations, there is a much more predictable, solvable, and imminent problem: climate change.

In the long run, the most important force affecting our evolutionary future will not be our medical technologies, but our reproductive decisions. Lynch is concerned about what he characterizes as “today’s ethical imperative for maximizing individual reproductive potential.” That’s not quite right — our society is increasingly recognizing an ethical imperative to maximize individuals’ reproductive choice. Our responsibility is to give people the information and tools to make their own decisions, which in some cases may include genetic counseling. Regardless of their genetics, different people will make different choices, sometimes choosing not to have children. Those choices, far more than any medical technology or any hypothetical eugenics program, will define the human gene pool of the future.