Discover how evolution continues to shape our species in the 21st century
We often imagine human evolution as a finished journey—a linear march from primitive ape-like creatures to modern humans, culminating in us. This comforting narrative suggests we've reached the pinnacle of evolutionary perfection. But what if this story is wrong?
"Of course humans are still evolving," says Jason Hodgson, an anthropologist and evolutionary geneticist at Anglia Ruskin University. "All living organisms that are in a population are evolving all the time" 4 .
The reality is that evolution never stops—it simply changes form. In the 21st century, we're not just evolving, we've become the single greatest force shaping evolution on our planet 7 .
For decades, scientists lacked the tools to observe human evolution in real time. Today, thanks to genetic research and massive datasets, we can now detect evolutionary changes as they occur 4 .
"Even within the past 1,000 years, lactase persistence as an allele is increasing," notes John Hawks, a paleoanthropologist at the University of Wisconsin-Madison 4 .
In Madagascar, a specific genetic variant providing resistance to malaria has proliferated throughout the population within just the past 2,000 years 4 .
Tibetan populations have developed unique genetic adaptations that allow them to thrive in low-oxygen environments over just a few thousand years.
Spread of lactase persistence in dairy-herding populations
Genetic variant proliferation in Madagascar population
Tibetan genetic adaptations to low-oxygen environments
One of the most compelling demonstrations of ongoing human evolution comes from an unexpected source: the Framingham Heart Study. This ambitious research project began in 1948 to track patterns of cardiovascular health across generations 4 .
When Stephen Stearns and his colleagues analyzed this data in 2010, they discovered natural selection was still operating on the Framingham population. Women of average height and weight were having more children than their counterparts, and these traits were heritable 4 .
| Trait | Change Detected | Interpretation |
|---|---|---|
| Height | Decrease in selected height | Natural selection favoring slightly shorter stature |
| Weight | Increase in selected weight | Selection favoring slightly higher body weight |
| Age at First Birth | Selection for earlier reproduction | Women having first child at younger ages had more children |
| Cholesterol Levels | Selection for lower cholesterol | Women with lower cholesterol had more children |
| Blood Pressure | Selection for lower systolic blood pressure | Women with lower blood pressure had more children |
Biological evolution occurs through four primary mechanisms, and all of them continue to operate in humans today.
Contrary to popular belief, natural selection isn't just about raw survival—it's about reproductive success.
"Most people think natural selection has stopped because modern medicine means everyone survives," says Hodgson. "But it's not even close to being equal." Unequal access to healthcare and resources means that selection pressures vary dramatically across different populations 4 .
In small populations, random fluctuations can significantly change gene frequencies—a process called genetic drift.
While humans are more connected than ever, many subgroups (religious communities, isolated populations) still experience drift. This mechanism unfolds fastest in smaller populations and can lead to significant genetic differences over time 4 .
When people migrate and have children with new populations, they create gene flow—the transfer of genetic variants from one population to another.
In our globalized world, this has accelerated dramatically. The genetic consequences are profound, creating new combinations of traits and introducing genetic diversity that evolution can act upon.
Every person is born with approximately 70 new genetic mutations on average that aren't derived from their parents 4 .
Most have no effect, a few are harmful, and occasionally one provides an advantage. This constant introduction of new genetic material provides the raw fuel for evolution. As Hodgson notes, "This is the largest the human population size has ever been," meaning more mutations are occurring now than at any point in human history 4 .
Studying ongoing human evolution requires sophisticated tools. Here are some key reagents and methods revolutionizing our understanding:
| Tool/Reagent | Function | Application in Evolution Research |
|---|---|---|
| CRISPR-Cas9 | Precise gene editing | Testing function of evolutionary genetic changes |
| DNA Sequencers | Reading genetic code | Comparing genomes across populations and time periods |
| UK Biobank Data | Genetic/health database | Identifying genes linked to survival and reproduction |
| Taq Polymerase | DNA amplification | Enabling PCR to study ancient DNA from ancestors |
| Bioinformatics Software | Analyzing genetic data | Detecting selection patterns in genomes |
These tools have enabled discoveries like the 2017 study led by Mostafavi that scanned human genomes to find genetic variants that become less common with age—evidence they're being selected against 4 . They found only two strong examples: a gene linked to heavy smoking in men and another associated with Alzheimer's risk, suggesting evolution has already removed many harmful variants from our population.
"Most people want to know, 'are we directionally changing as a species into something else?'" says Hawks. The unsatisfying but honest answer is that evolution doesn't work toward a predetermined destination 4 .
The future of human evolution depends on which pressures persist long enough to shape our gene pool. Could we see greater divergence between populations? Or more homogenization through mixing? Will space travel introduce entirely new selection pressures?
"I personally think that our genetics are going to continue to change, probably at an accelerated rate," Hawks says, "but I do not have a good basis for predicting how" 4 .
Perhaps the most dramatic way humans are changing evolution is by becoming the dominant selective force on Earth. We've entered the Anthropocene—a new geological epoch defined by human influence 7 .
Creatures from birds to insects are adapting to city life. German cockroaches have evolved resistance to virtually all our insecticides through a magnificent "detox enzyme" that functions like a biological Swiss Army knife 7 .
As climate change alters environments, species must adapt or move. Native plants in Nevada's Great Basin are evolving faster growth and more seeds in response to invasive cheatgrass and drought 7 .
At heavily contaminated mine sites in the UK, sweet vernal grass has evolved tolerance to high levels of zinc and lead—so different from its relatives that it now flowers at a different time, becoming a new species in the making 7 .
"We are shaping the evolutionary tree of life," says Sally Otto, an evolutionary biologist at the University of Wisconsin. "Somewhere in the last 200 years, we have become the species that most shapes the selective pressures of other species" 7 .
The evidence is clear and overwhelming: human evolution continues here and now. It operates in our genes, our bodies, and our communities. From the Framingham study to malaria-resistant genes in Madagascar to rapidly evolving cockroaches in our kitchens, the signs are everywhere once you know how to look.
The greatest myth we've told ourselves is that we've conquered biology. In reality, we remain works in progress—beings shaped by deep history but still being shaped today. Understanding this truth changes how we see ourselves: not as the finished product of evolution, but as active participants in its endless, fascinating story.
As Leger reflects, "There might be a contraction in diversity, but there will again be the same radiation" 7 . Evolution continues with or without us—but now, for the first time, we can watch it unfold and understand our role in the process.