Humans are still evolving, and the evidence is surprisingly abundant. From genetic shifts tied to diet and disease over the last few thousand years to anatomical changes documented in cadavers over the last two centuries, natural selection, genetic drift, and mutation continue to shape our species. What has changed is not whether evolution is happening, but how it operates in a world of agriculture, medicine, cities, and global migration. The story is richer and stranger than a simple yes-or-no answer suggests.
Diet Left Some of the Clearest Marks
If you want a clean example of recent human evolution, look at milk. The ability to digest lactose past childhood, known as lactase persistence, evolved independently in several populations that domesticated dairy animals. In most mammals, the enzyme that breaks down lactose in milk switches off after weaning. But in parts of Europe, East Africa, and the Middle East, genetic variants arose that keep the enzyme active into adulthood. The timing of these variants lines up with the origins of animal domestication and dairying.1PubMed Central. Evolution of lactase persistence: an example of human niche construction This is widely considered one of the most clear-cut cases of recent human evolution.2PubMed Central. Why and when was lactase persistence selected for? Insights from Central Asian herders and ancient DNA
What drove the selection is more complicated than “people who could drink milk got more calories.” A large analysis of ancient and modern genomes found that the frequency of lactase persistence did not track neatly with how much milk a prehistoric population consumed. Instead, the advantage of being able to digest milk seems to have been strongest during famines or outbreaks of infectious disease, when drinking raw milk without being able to digest it could cause dangerous diarrhea and dehydration. Population fluctuations, settlement density, and pathogen exposure turned out to be better predictors of how fast lactase persistence spread than the sheer amount of milk people were drinking.3Nature. Widespread milk exploitation in the European Neolithic and its lack of correlation with lactase persistence
Milk is not the only dietary pressure that reshaped our genes. Starch tells a parallel story. Populations that historically ate starch-heavy diets carry more copies of the gene that produces salivary amylase, the enzyme that begins breaking down starch in your mouth. People from populations with traditionally low-starch diets tend to have fewer copies. The number of copies correlates with how much amylase protein you produce, meaning the gene literally scaled up in populations where starches were a dietary staple.4PubMed Central. Diet and the evolution of human amylase gene copy number variation This is not ancient history in evolutionary terms. These changes have been accumulating over roughly the last ten thousand years, since agriculture took hold.
Living at Extremes Pushed Rapid Genetic Change
Some of the most dramatic evidence of recent evolution comes from populations living in environments that push human physiology to its limits. Tibetans have lived at altitudes above 4,000 meters for thousands of years, where oxygen levels are roughly 40 percent lower than at sea level. Genome-wide studies have identified a gene called EPAS1, sometimes nicknamed the “super athlete gene,” as a key player in their adaptation to low oxygen.5PubMed Central. Mitochondrial retrograde signaling initiates HIF-1α/BNIP3/NIX-mediated mitophagy in Tibetan high-altitude adaptation Variants in EPAS1 and other genes are strongly associated with blood-related traits like hemoglobin levels and folate metabolism, which together help Tibetans avoid the dangerously thick blood that lowlanders develop at high altitude.6PubMed Central. Genetic signatures of high-altitude adaptation in Tibetans
The genetic differences between Tibetans and Han Chinese at key positions in EPAS1 are stark. At one spot in the gene, an allele carried by about 86 percent of Tibetans shows up in only about 33 percent of the Han population. At another, about 76 percent of Tibetans carry one version compared to roughly 13 percent of Han Chinese.7PubMed Central. Genetic changes in the EPAS1 gene between Tibetan and Han ethnic groups and adaptation to the plateau hypoxic environment These are huge frequency differences for populations that share relatively recent common ancestry, a sign that selection has been intense.
Altitude is not the only extreme environment that left a genetic stamp. The Bajau people of Southeast Asia, sometimes called “Sea Nomads,” have spent generations diving to forage for food, routinely holding their breath for minutes at a time. Genetic analysis showed that natural selection on a gene called PDE10A has given the Bajau larger spleens than their neighbors, providing a bigger reservoir of oxygenated red blood cells that the body can release during a dive. There is also evidence of strong selection on a gene involved in the human diving reflex.8PubMed. Physiological and Genetic Adaptations to Diving in Sea Nomads Follow-up work suggested the larger spleen arises from increased thyroid hormone production linked to reduced expression of that same gene, though the exact pathway is still being worked out.9PubMed Central. An Erythropoietin-Independent Mechanism of Erythrocytic Precursor Proliferation Underlies Hypoxia Tolerance in Sea Nomads
Pandemics as Evolutionary Engines
Infectious disease has probably been the single most powerful selective force in human history. Malaria alone has driven the emergence of numerous genetic variants across tropical populations, including sickle cell trait, thalassemia, and a deficiency in an enzyme called G6PD. The classic example, first demonstrated in 1954, is that people carrying one copy of the sickle cell variant have less severe malaria infections than people with two copies of the normal hemoglobin gene.10PubMed. Genetic control of resistance to human malaria Genome-wide association studies of severe malaria have since confirmed the hemoglobin gene locus as the single strongest genetic signal, and additional variants affecting blood groups and immune regulation have been catalogued as well.11PubMed Central. Human genetic variations conferring resistance to malaria
The Black Death offers an even more compressed case study. By analyzing DNA from people who lived before, during, and after the 14th-century plague pandemic, researchers identified immune gene variants that were strongly selected during the outbreak. People who carried certain protective variants were more likely to survive the plague and pass those variants on. But here is the twist: those same protective variants overlap with alleles that today increase susceptibility to autoimmune diseases like Crohn’s disease and rheumatoid arthritis.12PubMed Central. Evolution of immune genes is associated with the Black Death In other words, the plague reshaped the European immune system in ways we are still living with. Further work has identified specific genes involved in antigen processing, ERAP1 and ERAP2, that were selected during the plague and now contribute to autoimmune disease susceptibility, including inflammatory bowel disease.13PubMed Central. Rare and common variants in ERAP1 and ERAP2 selected for in response to Yersinia pestis infection contribute to autoimmune disease including inflammatory bowel disease
This is a pattern worth sitting with. Evolution does not plan ahead. A variant that saves your life during a pandemic can quietly raise your risk of chronic illness centuries later when the pathogen is gone. The autoimmune diseases that plague modern societies may partly be the lingering cost of ancient survival.
Anatomical Changes in Real Time
Evolution does not only show up in the genome. Some changes are visible in the body. One striking example is the median artery, a blood vessel in the forearm that typically regresses before birth, replaced by the radial and ulnar arteries that adults normally rely on. In some people, the median artery persists into adulthood. An Australian cadaver study found that this persistent artery was present in about a third of people, and its prevalence had risen significantly from roughly 10 percent in the mid-1800s to over 30 percent by the late 1990s.14PubMed Central. Recently increased prevalence of the human median artery of the forearm: A microevolutionary change A more recent cadaver study found the artery in 43 percent of the limbs examined.15PLoS ONE. Prevalence and anatomical significance of the persistent median artery: A cadaveric study
Whether this counts as adaptive evolution or simply neutral drift is debated. One interpretation is that the rising prevalence represents “nearly neutral evolution,” meaning the trait is not strongly selected for or against, and its frequency has drifted upward over a few generations.16PubMed. Persistent median artery: paedogenesis of the antebrachial arterial system in the human body Either way, it is a measurable anatomical shift happening on a timescale of decades, not millennia.
Wisdom teeth tell a related story. An increasing proportion of people are born without one or more third molars. This absence, called third molar agenesis, is tied to smaller jaw and facial dimensions: on average, people missing all four wisdom teeth have jaw structures about 3 to 4 percent smaller than those who develop all of them, and the effect scales with the number of missing teeth.17PubMed Central. Third Molar Agenesis Is Associated with Facial Size Both sexes are affected similarly, and the pattern appears to reflect an ongoing evolutionary trend toward fewer molar teeth in humans.18PubMed Central. Sexual Dimorphism in Third Molar Agenesis in Humans with and without Agenesis of Other Teeth People who are missing other teeth are also significantly more likely to be missing wisdom teeth, with one study finding third molar agenesis prevalence of about 51 percent in the tooth-agenesis group compared with about 21 percent in controls.19PeerJ. Third molar agenesis in modern humans with and without agenesis of other teeth
We Are Getting Cooler
One of the more unexpected findings in recent years is that human body temperature has been declining. The famous 98.6°F (37°C) standard comes from measurements taken in the 19th century. A study of American health records spanning nearly 200 years found a steady decrease in body temperature by birth cohort: about 0.03°C per decade for both men and women. Men born in the early 1800s were on average about 0.6°C warmer than men born in the late 1900s.20PubMed Central. Decreasing human body temperature in the United States since the Industrial Revolution
This is not just an American phenomenon. A study of the Tsimané people, an indigenous population in Bolivia with high rates of infection, found the same downward trend, with body temperatures declining over a much shorter period. The leading explanation is that reduced chronic inflammation, driven by lower infection rates and better sanitation, means the body no longer needs to run as hot. Whether this represents genetic evolution, a purely environmental shift, or some interplay of the two remains an open question.21PubMed Central. Rapidly declining body temperature in a tropical human population But it is a measurable physiological change in our species happening across very different populations, in real time.
Does Modern Medicine Stop Evolution?
A common assumption is that medicine, sanitation, and technology have effectively halted natural selection in humans. The logic goes: if nearly everyone survives to reproduce, the filter that removes harmful variants no longer operates. There is some truth to this. What is exceptional about humans is our recent detachment from the natural environment and our ability to modify traits in ways that soften the impact of harmful mutations, from eyeglasses to insulin pumps to organ transplants. This leads to a relaxation of selection against mildly harmful mutations, including mutations that increase the mutation rate itself.22Genetics. Mutation and Human Exceptionalism: Our Future Genetic Load
But “relaxed selection” does not mean “no evolution.” It means the type and direction of selection have shifted. When survival-based selection weakens, other forms of selection become proportionally more important: who pairs up with whom, how many children different people have, whether certain genotypes are more likely to end up in stable partnerships. In a large dataset of roughly 250,000 people, researchers found signals of sex-differential selection affecting survival, reproductive success, and overall fitness, including genetic variants where the direction or strength of selection differed between men and women.23PLOS Biology. Polygenic signals of sex differences in selection in humans from the UK Biobank Evolution has not stopped. The selection pressures have rearranged.
New Mutations Keep the Engine Running
Even in the absence of strong natural selection, evolution continues because every new generation introduces fresh mutations. The rate of these new mutations is not fixed. A major factor is paternal age at conception. New single-nucleotide mutations in a child’s genome correlate strongly with how old the father was, with an estimated increase of about two new mutations per year of the father’s age. An exponential model estimated that paternal mutations roughly double every 16.5 years, and after accounting for random variation, the father’s age explained nearly all remaining differences in new mutation counts between families.24PubMed Central. Rate of de novo mutations and the importance of father’s age to disease risk
This matters for the trajectory of our species. In many industrialized countries, the average age at which people become parents has been climbing for decades. If older fathers contribute more new mutations per child, the total input of new genetic variation into the population is changing. Most of these mutations are neutral or mildly harmful, but some may occasionally be beneficial. Maternal age contributes too, though the effect is smaller.25PLOS ONE. Paternal Age Explains a Major Portion of De Novo Germline Mutation Rate Variability in Healthy Individuals Either way, the raw material for evolution keeps entering the gene pool with every birth.
What Actually Predicts Who Has Children Today
If you want to know where selection pressure is acting in a modern industrialized society, follow the reproduction. A study using the Wisconsin Longitudinal Study dataset found that the single strongest predictor of how many biological children someone had was whether they had ever been married, explaining about 73 percent of the variance in men and about 59 percent in women.26Evolution and Human Behavior. Contemporary selection pressures in modern societies? Which factors best explain variance in human reproduction and mating? That may sound like a cultural fact rather than an evolutionary one, but the distinction blurs quickly. If any genetic traits make a person more or less likely to form stable partnerships and have children within a given cultural system, those traits are under selection. The cultural environment is the selective environment.
This is the broader point people often miss when asking whether humans are still evolving. Evolution does not require saber-toothed predators or ice ages. It requires variation, inheritance, and differential reproduction. All three are still present. What counts as “fitness” just looks different now. It is less about surviving a harsh winter and more about navigating a complex social world.
Ancient DNA Revealed Far More Selection Than Anyone Expected
For a long time, detecting natural selection in humans was indirect. Researchers would look at patterns in modern genomes and infer that selection had occurred. The revolution in ancient DNA changed that. By extracting and sequencing DNA from human remains spanning thousands of years, scientists can now directly watch how allele frequencies shifted over time, rather than trying to reconstruct the past from the present.27PubMed Central. Insights into human adaptation from ancient DNA
A recent large-scale analysis applied a new method to DNA from over 8,400 West Eurasians who lived across the past 14,000 years, combined with data from over 6,500 contemporary people. By testing for consistent directional trends in allele frequency over time, the researchers identified 347 independent genomic regions with greater than 99 percent probability of having been under selection. That is an order of magnitude more signals than previous scans had found.28PubMed Central. Pervasive findings of directional selection realize the promise of ancient DNA to elucidate human adaptation The ability to sample genomes from multiple time points lets researchers pin down not just whether selection happened, but when it intensified and how fast it moved.29Evolution Letters. Inference of natural selection from ancient DNA
The implication is striking. Earlier methods were detecting only the tip of the iceberg. Human evolution over the last several thousand years has been far more pervasive than the field assumed even a decade ago.
Skin Color and the Sun
Skin pigmentation is one of the most visible examples of evolutionary adaptation, and the process is far from frozen. Human skin color varies enormously across populations, driven by differences in ultraviolet radiation at different latitudes. Darker skin protects against folate destruction and DNA damage in high-UV equatorial regions; lighter skin allows more vitamin D synthesis in low-UV northern latitudes. But this is not a simple two-gene story. Skin pigmentation is influenced by many genetic variants scattered across the genome, and it is further shaped by gene-culture interactions, like clothing, shelter, and dietary vitamin D supplementation, that modify the selection pressures.30PubMed Central. The genetic architecture of human skin pigmentation: evolution and adaptation across global populations
What makes pigmentation interesting from an ongoing-evolution standpoint is that modern migration has placed millions of people in UV environments their ancestors were not adapted to. Whether and how quickly selection will act on pigmentation in these new settings depends on factors like diet, lifestyle, and how strongly pigmentation-related traits affect survival and reproduction in modern conditions. The selective pressure is weaker than it was ten thousand years ago for populations that now get vitamin D from supplements and folate from fortified food, but it has not disappeared entirely. Skin cancer, vitamin D deficiency, and their downstream health effects are still part of the picture.
When Culture Becomes a Selective Force
One of the most important insights from recent evolutionary research is that culture does not just respond to biology. It drives it. The lactase persistence story is a prime example: the cultural innovation of dairying created the environment in which the genetic trait for digesting milk became advantageous. Starch digestion and amylase gene copy number tell the same kind of story. This feedback loop, where a cultural practice creates a new selection pressure that then reshapes the genome, is sometimes called gene-culture coevolution, and it may be the dominant mode of human evolution over the last ten thousand years.
Today’s cultural environment is creating novel pressures that have no precedent in human history. Artificial light at night, sedentary lifestyles, processed diets, exposure to thousands of synthetic chemicals, and shifting social structures all represent new environmental conditions. Research in other organisms has already shown that urbanization and artificial light can alter gene expression and circadian rhythms across just a few generations.31PubMed Central. Adaptation to Nighttime Light via Gene Expression Regulation in Drosophila suzukii Whether equivalent genetic shifts are occurring in human populations is an open and actively studied question. The conditions for selection are present. The timescales are just long enough that we might not notice while it is happening.