The future of human evolution

Aside, Card, CardGrid, LinkCard, Steps, Tabs, TabItem, Badge, } from '@astrojs/starlight/components';

Core idea

Natural selection has not stopped operating on Homo sapiens — but most of the pressures that shaped our anatomy for several million years (predation, starvation, communicable disease in childhood) have been muted, not abolished, by medicine, sanitation, agriculture, and technology. Cultural evolution has largely taken over the work that morphological evolution used to do. What remains of biological selection is harder to see: it acts mostly on fertility, metabolism, and the interaction between genes and a brand-new environment — and Wood is candid that whether it will produce measurable phenotypic change in any reasonable timeframe is genuinely unknown.

Author's argument: The future of our species is less likely to be limited by whether our bodies are up to the task. The weak link is that our genomes were shaped in circumstances very different from those we face today.

Why it matters

It is easy to assume one of two extremes: that humans are still "evolving normally" in the same Darwinian sense as our ancestors, or that we have "stepped outside evolution" entirely. Both are wrong, and the truth between them is medically and politically consequential. Chronic diseases of ageing — heart disease, type 2 diabetes, dementia — are not simply failures of modern lifestyles; they are partly the delayed cost of genes that were selected when life was short and fertility was the only currency that mattered. Understanding contemporary human evolution is therefore not an idle curiosity. It is the foundation of evolutionary medicine, a field that reframes many modern ailments as mismatches between an ancient genome and a recent environment.

Key takeaways

Mental model — selection pressures, then and now

Copy sourceZoom

What natural selection is still doing

Selection has not stopped — it has changed targets

Selection requires only three things: heritable variation, differences in reproduction, and a trait that links the two. All three still exist. What has changed is which traits matter. For most of our ancestors, surviving childhood was the binding constraint on reproduction. In high-income societies that constraint is gone — child mortality is below 1%, so almost every genome that reaches adolescence gets a chance to reproduce. The action has moved to fertility itself (age at first birth, completed family size, willingness to have children at all) and to gene-environment interactions that were previously invisible because nobody lived long enough to express them.

Lactase persistence — selection caught in the act

The cleanest modern example is lactase persistence, the retention of the enzyme that digests milk sugar into adulthood. Ancestrally, mammals — humans included — switch off lactase after weaning. But in populations that domesticated cattle and reindeer (Northern Europe, parts of East Africa, the Arabian Peninsula), a regulatory mutation that keeps the gene "on" for life spread rapidly within the last ~7,500 years. In some Northern European populations its frequency exceeds 90%; in East Asian and most Indigenous American populations it remains close to zero. That is one of the strongest signals of recent positive selection in any species, and it shows selection responding to a cultural invention — dairying — within a few hundred generations.

How medicine and technology change the equation

Buffering the old pressures

Vaccines, antibiotics, clean water, refrigeration, surgical obstetrics, and antihypertensives have removed or attenuated most of the killers that shaped our ancestors. The 18th-century demographic transition — beginning in Europe at the Industrial Revolution and now spreading globally — replaced a high-fertility / high-mortality regime with a low-fertility / low-mortality one. Most deaths in industrialised societies now occur late, from non-communicable diseases of ageing: heart disease, stroke, chronic respiratory disease, type 2 diabetes, cancer, dementia.

Creating new pressures we didn't anticipate

Buffering is never free. Three new pressures arrive with modernity. Metabolic mismatch: genes that promoted efficient calorie storage in lean environments now predispose carriers to obesity and diabetes in calorie-abundant ones. Novel pathogens: dense urban living, globalised travel, and zoonotic spillover (SARS-CoV-2, HIV, influenza) introduce diseases we have not co-evolved with. Antibiotic resistance: our most powerful intervention is generating selection pressure on bacteria faster than we can develop new drugs.

Cultural evolution as the dominant mode

Adapting the environment, not the body

When a human population needs to survive at high altitude, the species response is no longer to wait for selection to reshape lung capacity over thousands of generations. It is to build oxygen masks, design pressurised cabins, manufacture supplemental oxygen. Cultural evolution operates on the timescale of years; biological evolution on the timescale of millennia. For any well-defined problem with a technological solution, culture wins.

This is why morphological evolution has been "largely, but not entirely, superseded." Most modern survival challenges are met by tools, institutions, and shared knowledge. The body that ten thousand generations of selection produced is, for most everyday purposes, good enough — and where it isn't, we engineer around it rather than wait for it to change.

Where culture cannot reach

But cultural evolution has blind spots. It cannot reach inside the genome to fix a pleiotropic trade-off. It cannot prevent novel pathogens from finding hosts. It cannot, by itself, reorganise human reproductive behaviour (people choose how many children to have, and that choice is itself becoming a selection pressure). Anywhere culture fails to fully buffer a biological reality, selection still has something to act on.

What to expect — and what to be uncertain about

Plausible near-term directions

A short list of traits currently showing measurable selection signals in living populations includes: age at first reproduction (selection appears to favour earlier, in some societies), completed family size, resistance to specific local diseases (sickle cell variants against malaria continue to be selected in endemic regions), and continuing diet-related adaptations like lactase persistence and starch-digesting amylase copy number. None of these will produce a visibly different species. They will subtly shift allele frequencies within populations over the coming centuries.

Wood's honest uncertainty

Whether Homo sapiens will continue evolving in measurable phenotypic ways is genuinely open. Three reasons for genuine doubt: (1) selection coefficients on most traits are tiny in low-mortality societies, so even real signals take many generations to surface; (2) genome editing, embryo selection, and other biotechnologies may begin to replace natural selection with deliberate intervention, scrambling the question of "evolution" altogether; (3) cultural evolution is now so dominant that biological change may simply not matter much to human outcomes for the foreseeable future.

Example: the type 2 diabetes mismatch

Consider the thrifty-genotype hypothesis as a worked illustration of how all the above interlocks. A genetic variant that makes the body unusually efficient at storing energy as fat would have been advantageous to a hunter-gatherer experiencing periodic food scarcity — the carrier survives the lean season and reproduces. The variant spreads. Ten thousand years later, the same carrier lives in a city where calories are abundant, cheap, refined, and never far away. The same metabolic setting now produces visceral obesity, insulin resistance, and type 2 diabetes by age 50. The gene has not changed. The environment has changed, and the gene's effect — which is the only thing selection ever "sees" — has flipped from advantageous to harmful.

This is why evolutionary medicine matters. The disease is real, but the framing matters: it is not a body failing in isolation, it is an ancient genome encountering a modern grocery store. The therapeutic implications are different — and so are the public-health ones.

Related material