Are Humans Still Evolving? ‘Maybe More Rapidly Than Ever,’ Says Scientist – Newsweek

It is often assumed that modern humans are no longer evolving. But there is now considerable agreement among scientists that evolution is still affecting our speciesand this process is taking place "more rapidly" than ever before, one expert told Newsweek.

While cultural and technological innovations now appear to be the main drivers of adaptation for modern humans, this has not replaced biological adaptation, according to scientists.

"I don't think [the question of whether humans are still evolving] is fully appreciated by the general public," Michael Granatosky, an evolutionary biomechanist at the New York Institute of Technology, told Newsweek. "Perceptions of evolution tout the phrase 'survival of the fittest', which automatically recalls epic battles between fighting individuals vying for a mate, or a ragtag bunch of animals surviving a cataclysmic event beyond all odds."

"With these images, it is tempting to assume modern populations are no longer under selective pressures. However, evolution simply means a change in a population's gene pool over successive generations. With this broader definition, I do not believe there is considerable debate among evolutionary biologists that humans are still evolving," he said.

From a genetic perspective, evolution is defined as a change in the frequency of certain genes through time, Jason Hodgson, an anthropologist and evolutionary geneticist at Anglia Ruskin University in the United Kingdom, told Newsweek.

Populations evolve in two primary ways: genetic drift and natural selection. Genetic drift refers to random fluctuations in the frequencies of certain genes between generations in populations.

"Some generations a genetic variant will increase in frequency, some generations it will decrease in frequency. However, it is always occurring," Hodgson said. "The strength of genetic drift depends on the size of the population, with small populations experiencing more drift and large populations experiencing less. The ultimate fate of any genetic variant evolving through genetic drift is either to go extinct, or to completely replace all other variants in the population and become fixed."

Natural selection, on the other hand, which people are more familiar with, occurs when a genetic variant provides a reproductive advantage to individuals that carry it. Changes in gene frequency due to natural selection are not random. The favored variant increases in frequency while all other variants decrease.

"The ultimate fate of a variant evolving through natural selection is to replace all other variants in the population," Hodgson said. "Perhaps counterintuitively, natural selection is a stronger force in larger populations. This is because in large populations selection is not countered by genetic drift."

Both natural selection and genetic drift continue to affect our species, thus, humans are "undoubtedly" still evolving, Hodgson said. Genetic drift continues to change the frequency of allelesdifferent versions, or variants, of a given geneas it does in all biological populations.

"The census size of humans has now surpassed 8 billion people. In a population this size, genetic drift should be almost negligible. However, in reality humans are subdivided into much smaller groups, within which people are more likely to choose their mates," Hodgson said. "This means that in practice evolution occurs in much smaller groups, and genetic drift does still operate."

Similarly, natural selection is also still operating, although the drivers are now different compared to when humans were primarily living as hunter-gatherers thousands of years ago.

"In terms of pressures, several things are happening. For one thing, the pressures that used to drive our evolution in hunter-gatherer societiesresistance to disease and parasites, strength to defend yourself from lions or else kill someone from a rival tribe, or kill someone over a woman (traditionally, one of the leading causes of murder in hunter-gatherer societies)have largely been removed. Basically, the things that used to cull us from the population largely aren't operating," Nick Longrich, a paleontologist and evolutionary biologist at the University of Bath in the United Kingdom, told Newsweek.

"You might think this would end natural selection, but instead it does two things. One is that it alters the direction of selection: if selection isn't operating on these things, it increasingly operates on other things, or might select against features that were once useful adaptations," he said.

For example, access to things like healthcare and birth control is highly variable within and among human groups. This means that the rates of people surviving to a given age and reproductive success are also variable.

"Not all evolutionary change is to do with things like death from disease, or risks faced from a harsh environment," Hodgson said. "Anything that creates variation in birth rates among groups, so long as there are differences in allele frequencies among those groups, will create evolutionary change. Because allele frequencies vary among human groups, any difference in reproductive rate among those groups will cause evolution if we are considering the human species as a whole."

"It is my belief that cultural variation with respect to things like preference for large families or small families will drive much of the evolution of humans in the near future. Lots of the evolution we see on a species-wide scale will be driven by demographic differences among populations that happen to correlate with differences in gene frequencies among those populations. Genes that are common in populations that are expanding will increase in frequency, and genes that are common in populations that are contracting will decrease in frequency," he said.

There are several notable examples of evolution among modern humans in our relatively recent history. In fact, Longrich said: "Humans are evolving rapidlymaybe more rapidly than we've ever been evolving before."

For example, "our brain size is evolving[they] have actually become smaller over the past 10,000 years since we started living in civilization," he said. "Brains seem to be smaller now than even in Greek or Roman times."

We have also adapted to newly available food sources, for examplesome populations, particularly those of European descent, have developed the ability to tolerate milk into adulthood.

Skin color has changed as human populations moved into new climates. And resistance to various diseases has emerged as a result of plagues like the Black Death and smallpox.

"The most recent example of clear natural selection in humans is perhaps selection for resistance to vivax malaria in Madagascar," Hodgson said.

Over the past 2,000 years there has been strong selection for resistance to the diseasewhich is a form of malaria caused by the Plasmodium vivax parasitein Madagascar.

"We can estimate that having resistance to vivax malaria results in about 7 percent greater reproductive success," Hodgson said. "[The selection] is very likely to be ongoing since medical care is highly limited in much of Madagascar."

The recent COVID pandemic may also have resulted in evolutionary pressures on our species, according to the scientists.

"During the pandemic, we learned that there is natural variation as to how individuals responded to infection," Granatosky said. "Such variation serves as the basis for evolution to act. Perhaps the most interesting thing about the COVID-19 pandemic was its global nature. Rarely do such events affect an entire species so dramatically."

To have an effect, the virus does not need to kill people, it just needs to affect their long-term reproductive output, according to Longrich.

"We've definitely evolved in 2020-2023," he said. "There are a lot of negative consequences associated with non-lethal infectionsfatigue, depression, brain fog, etcetera, and currently it seems like the virus is just going to keep circulating indefinitely, which increases the odds that sooner or later people get an adverse reaction."

"We probably won't know the effects for another 50 years, but people with an innate resistance to the virus are at a distinct advantage relative to everyone else, and people whose genes make them vulnerable are at a disadvantage, and it's hit pretty much every person on the planet. I don't think it will radically reshape us as a species, but I'd be surprised if it doesn't leave a lasting imprint on our genetic diversity that will be detectable for generations," he said.

Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.

Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.

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Are Humans Still Evolving? 'Maybe More Rapidly Than Ever,' Says Scientist - Newsweek