Evolution

Like anyone who believes in the validity of science, I am a Darwinian. I believe that all life forms, including human beings, evolved over long periods from simpler forms. I do not believe in Adam and Eve and I do not believe any of the other origin myths.

I believe that for almost all species, the process of evolution by natural selection is continuing. I doubt, however, that the evolution of human beings by natural selection is continuing. Why does this matter? Because, as I will try to show, natural selection is a brutal, cruel process, and if we are free from it, our lives are immeasurably better.

Charles Darwin’s seminal book of 1859 was entitled The Origin of Species, By Means of Natural Selection or the Preservation of Favored Races in the Struggle for Life. The reason for citing the full title is that his entire argument is summarized in those words. All life forms have origins; that is, they evolved from other forms. The process of evolution is natural; it is not divine or miraculous. Life of all forms is a struggle. No specimen of any species escapes death, and few survive even to reproduce. The ones that do survive to reproduce have won the struggle for life. They are selected by nature because of their superior fitness to reproduce.

Darwin grounded his thinking in the writing of Thomas Malthus, whose Essay on Population (first edition of many, 1798) posited that life for human beings was a struggle. Population growth tended to exceed the growth of food production, so humans were always on the edge of starvation, and many did starve. If for a time the availability of food exceeded the demand, the respite was temporary, because deaths would fall, the population would grow without limit, and before long starvation would resume, only this time in greater numbers because the population would be larger. Malthusianism was why economics was known in the 19th century as the dismal science.

From the perspective of more than two centuries, we now know that Malthus was wrong, or at least that his predictions have so far been wrong. Improvements in food and living conditions lowered death rates, as he foresaw, but they eventually were accompanied by falling birth rates, so that the material improvements have not been dissipated by an endlessly growing population. Attempts to improve living conditions are not doomed to failure.

Darwin used Malthus’s principles for a different purpose, however, not to predict the future of the human condition, but to understand the evolution of all species. He thought that the principles applied even more to other species than to humans.

Think of the differences in reproductive numbers. The typical human woman has just one baby at a time. In the premodern era, with uncontrolled fertility, a woman who survived through the childbearing years (and many did not) would bear perhaps a dozen children, of whom maybe three would survive to adulthood, but only half the survivors would be female, capable of further reproduction. In normal times, this led to slow population growth, but life was punctuated with catastrophes (diseases, famines, wars) when death rates spiked and the population fell. The result, over time, was that although women had many children, by our standards, population growth was roughly zero.

Of course, the question of which women survived to reproduce is complicated. In every human society we know of, the factors have included class, oppression, differential access to health care and other social factors. But in societies with such high death rates that most people did not survive to reproduce, the factors also included biological fitness.

Darwin was influenced by Malthus, but The Origin of Species did not discuss human evolution, only the development of non-human species,

Animals typically have litters much greater than one. Think of mice and wolves. Yet the population of mice and wolves does not grow over time, because most of the females die before they can reproduce. Which ones survive? The Darwinian principle is that the fittest survive.

When you turn from fauna to flora, the numbers become staggering. I am making up the following example, but I don’t think I am overestimating. Let us presume that a typical apple tree bears about 500 apples a year, and continues bearing for 40 years. That makes 20,000 apples from one tree. If each apple has five seeds, that makes 100,000 seeds from one tree, each of which has the potential to create a new tree. You would think the population of apple trees would explode, but in fact the number of trees stays roughly constant. In other words, 99,999 of those seeds disappear before producing a new tree. The probability of survival to reproduction is 0.00001. Which one survives to reproduce? The heart of Darwinian theory is that the process is not random; the fittest survive.

Return for a moment to Darwin’s title, which includes the words The Struggle for Life. That is why I wrote at the top that natural selection is brutal and cruel. All those baby mice, all those baby wolves and all those apple seeds are struggling to reproduce, but almost all are destroyed before they can fulfill their biological destiny. It’s a war out there, not a game with fair rules and neutral referees. The only rule, as far as Darwin could tell, was that the fittest survived.

This brings me to my skepticism that human beings are continuing to evolve by natural selection. For most people (not all), life is no longer a struggle for survival. We do not live in a Malthusian world, where starvation is imminent. Death rates have fallen to very low levels in the more developed countries, and they have fallen considerably in the less developed countries. The great majority of babies escape infant mortality, and they survive long enough to reproduce. Not all, but most. This, I think, is the greatest achievement of the human species, the creation of a world in which most babies are guaranteed a long and relatively healthy life.

Nature is not selecting the fittest humans to reproduce; it is allowing almost everyone to reproduce. Moreover, for most women, reproduction is a choice, not a biological necessity. Most are choosing a low rate of reproduction, often a zero rate, and in most cases the choice is not related to biological fitness.

Natural selection no longer guides human evolution.

I have tried to formulate that sentence carefully. I am not claiming that the human species will remain unchanged. I am making a more modest claim, that whatever changes occur in the fairly foreseeable future will be determined by forces other than natural selection.

This is consistent with what Darwin wrote in The Origin of Species. He said explicitly that while natural selection was the main engine of evolution, there could be others.

People have posited many other causes of evolution. I think some of them are implausible, but not all. Among the other candidates are:

1.      Lamarckism. In the 19th century, most naturalists eventually accepted the idea of evolution, but rejected Darwin’s explanation of it. Rather than natural selection, they  preferred the theory of Jean-Baptiste Lamarck. He believed in evolution by acquired characteristics. Why do giraffes have long necks? They stretched them trying to get to fruits high in trees. The acquired characteristic of a stretched neck was passed on to their offspring. That explanation seemed more plausible than natural selection. Lamarckism gave way to natural selection only in the 20th century, once the theory of genetics was developed. 

2.     Epigenetics. This is the theory that environmental factors may affect our DNA, and through this process our evolution. Perhaps the most likely environmental factor is radiation. Some scientists think that catastrophic experiences, like the Holocaust, can alter DNA and hence evolution.

3.     Intelligent design. This is the idea that God (the intelligent designer) controls the direction of evolution. To believe in intelligent design requires a faith in the supernatural that I lack.

4.     Orthogenesis. This is the idea that the full design of all the evolution to follow was contained in the original life forms.

5.     Sampling bias. When an offspring is produced, it receives a sample of the genes of the parents, not the full set of genes. Some scientists think that a bias in sample selection could affect evolution.

I am not competent to judge between these theories. Some of these factors may affect human evolution. All I want to assert here is that natural selection no longer governs human evolution.

I hasten to add that this holiday from natural selection may be a brief moment. The good times of low global death rates may not last. We are making profligate use of fossil fuels, to such an extent that we may be destroying the ecological foundation on which human life, and much else, depend. Future generations may descend to a situation in which starvation is once again the norm and only the favored few, the fittest, survive. Natural selection may return for human beings.

That would be a disaster, because natural selection is brutal and cruel. Let us hope we do not get there. As of now, the great majority of female human babies survive through the reproductive period. They are not selected for reproduction by a natural process.  Human beings are enjoying at least a temporary pause in the Darwinian mechanism.

John Isbister

July 25, 2026

 

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