Science Questions with Surprising Answers
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Dr. Christopher S. Baird

When did humans stop evolving?

Category: Biology      Published: September 26, 2013

jug of milk
Humans are still evolving. The ability of adult humans to digest milk is a recent evolutionary change brought about by the domestication of the cow. Public Domain Image, source: Christopher S. Baird.

Humans have never stopped evolving and continue to do so today. Evolution is a slow process that takes many generations of reproduction to become evident. Because humans take so long to reproduce, it takes hundreds to thousands of years for changes in humans to become evident. We simply don't notice the evolution of humans from day to day because it is happening so slowly. But creatures that reproduce more quickly also evolve more quickly. For instance, bacteria can reproduce within 20 minutes, so their evolution can be watched by scientists over the course of a few days. All creatures are always evolving. There is no way to stop evolution.

Some people think that humans' development of technology has enabled us to short-circuit evolution, or step outside of evolution. But evolution is not some magical transformation that happens in the wild to dim-witted creatures, propelling them ever towards greater complexity. Evolution is just the observation that creatures change over time because varieties that do best at surviving and reproducing in a given environment are more able to pass their genetic traits on to the next generation. Technology is part of evolution, as is poetry and economics, in so far as they affect survival and reproduction, and can be passed on genetically. Those races that use technology in order to better survive and reproduce are able to pass along their technology-minded genes to the next generation. Technology is not evidence that the evolutionary process has been destroyed or side-stepped. Rather, technology is direct evidence that evolution is still at work. Technology is so effective at helping the human species to survive and reproduce that humans have come to dominate the globe in the process, and technology has proliferated.

You many counter, "But modern medicine has kept alive people with disease-causing genes who should have been weeded out by evolution. Humans should be getting stronger as the weaker people die and fail to reproduce, but modern medicine is keeping the weaker people alive and has therefore bypassed evolution." My response to this is: there is no "should" in evolution. Evolution is not goal-oriented; it has no end purpose. Confusing improvement with evolution leads to misguided practices such as eugenics. Medicine does not bypass evolution; it is just evolution in a different form. Groups of people who have brains that are adept at developing and applying modern medicine survive more and pass along their brains to their children.

We have to be very careful here in the words we use. Evolution in the strict scientific sense is the passing on of advantageous traits from one generation to the next through the genes, and not through education or reform. Giving my son a good education will help him personally, but it does not really change his genetic code and therefore is not part of evolution. On the other hand, having a genetic mutation that gives me a more powerful brain, which I then use to create technology that aids in my survival and reproduction, is evolution. I am able to pass on to my son the gene so that he has a more powerful brain as well.

So what will humans look like in 500 years if they are still evolving? This is a hard thing to predict. Humans and human society are so complex at this point that you can't really pinpoint one isolated trait besides their big brains that makes them survive and reproduce better. Accurate scientific predictions about the evolution of humans are nearly impossible. Weather forecasters can't predict what a handful of elements in the sky will do a week from now, so predicting what the complex web of humanity will become in hundreds of years is out of the question. But, for the sake of illustrating how evolution works, we can engage in some unfounded speculation. The leading causes of death may give us some hints about future human evolution. We have to be careful and only consider the leading causes of death among people who are young enough to reproduce, say, before the age of 35. Those that have a genetic makeup that predisposes them to better survive the leading causes of death among those younger than 35 years will be able to pass their genes on to the next generation and therefore influence the course of human evolution. According to the CDC, the leading causes of death in the US for people younger than 35 are unintentional injuries (such as car accidents), suicide, homicide, and cancer. Whatever biological traits enable a person in the US to avoid fatal injuries, suicide, homicide, and cancer will become the traits more pronounced in humans in the US as they evolve. For example, humans could evolve to become less risky (thus avoiding accidents), more religious (thus avoiding suicides and homicides), and more disgusted by smoking and alcohol (thus avoiding lung and liver cancer). Note that heart disease is one of the top killers overall in the US. You may be tempted to conclude that humans will evolve to be more resistant to heart disease, or will evolve to crave heart-healthy foods more. But if you look at the CDC data of mortality by age, you find that heart disease is only a top killer for people over 45 years old, which is passed the main child-bearing years. Heart disease therefore has little influence on reproduction, and, by extension, little influence on evolution.

Another way to get some hints into future human evolution is to look at births instead of deaths. The countries with the highest birth rates are in Africa. Even though such countries have high death rates, the birth rate is high enough to compensate for this. This fact is a hint that humans may evolve to look more like native Africans. If we instead look at behavior instead of nationality, a consistent factor linked to high birth rate across all cultures is religiosity. People with strong religious sentiments tend to have more children. Furthermore, the degree of religiosity is directly proportional to the amount of children a person has. This fact hints that humans are destined to evolve to become more religious. In summary, if these hints are any guide, we can expect humans to evolve in the next few hundred years to be more religious, less risky, less drawn to drugs, and more African in appearance. Again, these ideas are pure speculation and are meant only to illustrate how evolution works through survival and reproduction, and not to make actual scientific predictions about the future of human evolution (which is nearly impossible).

Note that it is very unlikely at this point in human evolution that we will sprout wings, a third arm, or purple skin. The survival advantages of such major morphological changes have long been surpassed by applications of human intelligence. Humans can already use their brains to build airplanes. There is therefore no survival advantage we would gain from growing wings. Any disadvantage that humans have because of basic structure has been compensated for by human-made machines. The future of human evolution will therefore most likely involve the brain and the chemical/hormonal systems that support the brain.

Topics: evolution, human evolution, reproduction, selection