The evolution of our species is often symbolized by the transformation of a four-legged chimpanzee into an upright hunter.
But our story does not end there.
Today, evidence suggests that humans continue to evolve, and it shows in our very physiology: from our skin to our eyes to our blood.
Take, for example, our instinct. It contains one of the strongest documented examples of modern natural selection that scientists have ever discovered.
About 10,000 years ago, humans in some parts of the world began domesticating cows and other grazers. Then they learned to milk these animals.
But the problem was that the intestines of adult mammals were not prepared for lactose.
However, some of our ancestors had genetic variants that allowed them to tolerate dairy products without getting sick.
It made all the difference.
Modern genetic studies in Europe, East Africa, and the Middle East suggest that over time, lactose tolerance variants have spread through natural selection.
Today, this is probably the reason why 30 to 35 percent of the world’s adult population can tolerate lactose.
Meanwhile, in the Andes of South America, it was not milk but the potato that shaped the evolution of the human gut.
The Quechua people, of indigenous highland Andean ancestry, were among the first in the world to domesticate the potato.
Earlier this year, researchers discovered that this population appeared to be better equipped to digest starch than almost any other population on Earth.
“Biologists have long suspected that different groups of humans evolved genetic adaptations in response to their diet,” said evolutionary anthropologist Omer Gokcumen of the University at Buffalo.
“But there are very few cases where the evidence is this strong.”
When the ancestors of Andean natives began growing potatoes, those with a higher number of copies of a certain genetic variant likely gained an evolutionary advantage.
About 10,000 years ago, those with about 10 or more copies had a survival or reproductive advantage of 1.24% per generation.
It’s not much, but it’s enough to add up over millennia.
“Those with lower copy numbers were eliminated from the population over time, perhaps because they had fewer descendants, and those with higher copy numbers remained,” Gokcumen said.
Related: Humans in the Andes Appear to Have Evolved an Unusual Genetic Ability
Adaptations to our environment also run in our veins. Take for example the humans who live on the Tibetan plateau.
Here, life at high altitude for more than 10,000 years has led to fascinating adaptations within local communities.
For years, anthropologist Cynthia Beall of Case Western Reserve University in the United States has studied how the human body responds to lack of oxygen at high altitudes.
In 2024, she and her team reported evidence showing that Tibetan communities possess adaptive traits that improve their blood’s ability to deliver oxygen.
“This is a case of continuing natural selection,” Beall said at the time.
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The example is particularly strong given the association with reproduction.
Among 417 Nepalese women who had lived their entire lives at altitudes above 3,500 meters (11,480 feet), those with the highest live birth rate had red blood cells with unusually high oxygen saturation.
“We knew that higher hemoglobin oxygen saturation was beneficial; we now understand that the higher the saturation, the more beneficial it is,” Beall told ScienceAlert’s Michelle Starr.
“The number of live births quantifies the benefits.”
Some signs of natural selection can also be seen outside our bodies.
Skin pigmentation, for example, is a commonly cited example of our species’ adaptation to sun exposure.
It is widely believed that early humans in Africa had darker skin because it provided protection against DNA damage caused by strong ultraviolet rays.
But further from the equator, selective pressures seem to favor lighter skin.
This year, the largest ancient DNA dataset to date revealed evidence of natural selection among Western Eurasians.
Nearly 500 genetic variants have been identified in this lineage which has changed over the past 10,000 years.
Many corresponded to known physiological traits, such as body fat, celiac disease or schizophrenia.
But one of the strongest evolutionary signals in the dataset concerned skin pigmentation.
Over the past 10,000 years, the findings suggest that genetic variants associated with lighter pigmentation have become more common in this human population.
“This plausibly reflects selection for increased vitamin D synthesis in low sunlight regions among farmers with little vitamin D in their diet,” the authors suggest.
Even the way you are reading this article right now could be the product of natural selection.
Myopia, or nearsightedness, has increased in recent decades.
In 2021, researchers found evidence in the UK Biobank that the disease is associated with mutant alleles.
The frequency of these alleles has increased over the past 25 years, perhaps due to natural selection.
Although myopia can be a disadvantage for survival, certain genetic variants linked to this trait may have other reproductive advantages.
This is called “antagonistic pleiotropy.” This is an evolutionary theory that certain genes confer beneficial effects early in life, but cause harmful effects later.
“We estimate that, in the UK alone, natural selection adds more than 100,000 cases of myopia per generation, and argue that antagonistic pleiotropy must be widely considered to explain the spread of apparently disadvantageous phenotypes in humans and beyond,” the authors of the 2021 study concluded.
Evolution doesn’t always make us healthier or fitter.
Related: The ‘shadow’ of evolution that explains why long life comes at a cost
Natural selection favors genes that help us survive, but sometimes they can result in other traits that aren’t so advantageous.
As the modern world continues to transform around us, the evolutionary pressures that shape our species will also evolve.
Human evolution is far from over.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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