The short answer
Yes, in the scientific sense, human populations are still evolving. Evolution means a change in the frequency of genetic variants in a population from one generation to the next. As long as people are born with genetic differences and those differences are passed on at different rates, populations change. There is no point at which a species stops evolving, and nothing about modern life switches the process off.
The harder questions are about how fast, in what direction and through which mechanisms. Here the honest answer involves uncertainty, because human generations are long, and a few hundred years is a very short time to measure.
More than natural selection
Natural selection gets most of the attention, but several processes change gene frequencies:
- Mutation introduces new variants. Every person carries a small number of new mutations that neither parent had, and these are the raw material for change.
- Natural selection makes variants that improve survival or reproduction more common.
- Genetic drift is random change in the frequency of variants, which matters most in small populations.
- Gene flow is the movement of variants between populations when people migrate and have children together.
Today, global travel has greatly increased gene flow, mixing populations that were once relatively separate. That tends to reduce differences between groups rather than create new ones. Drift can still matter when small groups become isolated, and mutation continues quietly in everyone.
Evidence of recent selection
Several well-studied cases suggest selection has acted on humans in the relatively recent past, and some probably still operates.
Lactase persistence. Most mammals lose the ability to digest milk sugar after infancy. In populations with a long history of keeping dairy animals, a larger share of adults keep producing the enzyme. Genetic studies show this has arisen through different variants in different parts of the world, which is a sign of repeated adaptation to a similar way of life.
Sickle cell and malaria. In regions where malaria has been common, people who carry one copy of the sickle cell variant tend to have some protection against severe malaria, while people with two copies can develop serious illness. This balance is why the variant has stayed relatively common in some places. It shows how the environment, including a disease, shapes which inherited traits spread.
High altitude. Populations living on the Tibetan Plateau and in other high regions show genetic differences associated with coping with low oxygen. These are widely studied, though the details differ between regions.
Diving populations. Research on the Bajau, who traditionally spend much of their lives diving from boats in Southeast Asia, has reported differences that may relate to spleen size. This is an interesting finding, but it is a single line of research, and scientists remain cautious about its interpretation.
Does modern medicine stop evolution?
A common idea is that medicine, sanitation and food supply have ended natural selection for humans. This is only partly right. Selection acts through differences in how many children people have, not only through who survives to adulthood. As long as people with different genetic variants have different numbers of children who survive, selection can act.
It is true that modern medicine has greatly lowered childhood mortality in many countries, and so has changed which pressures are strongest. Variants that were once dangerous can now be managed, which means selection against them is weaker. Scientists call this relaxed selection. It does not mean harmful variants will take over quickly; changes of that kind would be very slow and are hard to predict.
Medicine also does not remove all pressures. New infectious diseases, differences in fertility and changing environments continue to matter. Bacteria, meanwhile, evolve very quickly in response to our treatments, which is why antibiotic resistance is a real and measurable example of evolution happening in front of us, though in microbes rather than in people.
Can we measure it in people today?
Some researchers have looked at large datasets for signs of selection on traits like age at first birth, height or cholesterol levels. Results exist, but they are small, are sometimes hard to separate from cultural change and should be treated with care. Genome studies can also find patterns that suggest recent selection on certain genes, though interpreting them takes careful statistics, and different methods do not always agree.
It is also important to separate genetic change from other kinds of change. Average height, life expectancy and many other traits have changed over the last century largely because of nutrition, health care and living conditions. These are changes in the environment’s effect on people, not changes in genes.
What it does not mean
Evolution is not a march toward a “better” human, and it has no goal. Nothing guarantees that people will become smarter, taller or healthier through evolution. Popular predictions about humans of the far future, such as larger heads or fewer toes, are speculation rather than scientific forecasts. Culture and technology add complexity: people change their own environments quickly, and those changes alter the pressures that selection responds to.
Evolution also acts on populations, not on individuals. No one evolves during their own lifetime, although individuals can adapt in other ways, such as becoming fitter or acclimatizing to altitude.
A balanced summary
Human evolution continues because the basic ingredients, genetic variation and different rates of reproduction, are still present. Some of the best-supported examples involve diet, disease and altitude, and others are less certain. How strongly selection acts now, compared with the past, is a subject of ongoing research. The most defensible position is that people are still evolving, that the pace and direction are hard to measure, and that anyone claiming to know where it is heading is going beyond the evidence.