Evolution is defined as a change in the inherited traits of a population over successive generations. The question of whether humans are still evolving is often met with the misconception that technological advancement has somehow insulated us from this fundamental biological process. However, the answer is definitively yes; human evolution has not stopped, and in some ways, it is occurring at an accelerated pace due to the new environments we have created. The mechanisms that drove change in our distant ancestors remain active today, constantly reshaping the human gene pool.
The Core Mechanisms of Change
Evolution is driven by several forces, and natural selection is only one component actively shaping human populations. Genetic drift, which is the random fluctuation of allele frequencies due to chance events, remains a significant factor, particularly in isolated or smaller populations. This non-adaptive mechanism can cause certain genetic variations to become more or less common, especially following a “founder effect” where a small group separates to establish a new community.
Gene flow, or migration, is arguably the most dramatic evolutionary force acting on humans today, driven by global mobility and urbanization. The constant movement of people across continents rapidly mixes previously separated gene pools, introducing new genetic variants into populations that were once distinct. This massive-scale interbreeding tends to diminish genetic differences between large human groups.
Natural selection, the differential survival and reproduction of individuals based on their traits, also persists, even if its pressures have shifted. The environment, whether natural or human-made, still favors certain genetic variants over others.
Why Evolution Has Not Stalled
The common belief that modern medicine and technology have halted human evolution is flawed. Selection does not require high mortality rates; it requires differences in reproductive success. While infant and child mortality has dramatically decreased, differential birth rates and the number of surviving offspring still cause certain heritable traits to spread or diminish in the population.
Reproductive fitness is the true engine of selection. Traits that affect fertility, the age of first reproduction, or the duration of the reproductive lifespan are under powerful selection pressure today. For instance, studies have shown selection acting to lengthen the female reproductive period by favoring genes associated with earlier age at first birth and later menopause.
Our modern lifestyle introduces new selective pressures that our ancestors never faced. The widespread use of antibiotics has created an environment where resistance to common infections is now an advantage. Likewise, the rise of chronic conditions like type 2 diabetes and heart disease creates a new form of selection based on metabolic and physiological resilience.
Observable Evidence of Recent Change
Evidence of recent human evolution is linked to major cultural shifts.
The most cited example is lactase persistence, the ability for adults to digest the milk sugar lactose. This trait was strongly selected for following the domestication of cattle. The European variant of the persistence allele, C/T(-13910), is estimated to be between 5,000 and 12,000 years old, demonstrating rapid adaptation.
Significant changes are also observable in anatomy and vascular systems. The prevalence of the median artery in the forearm, a vessel that typically regresses before birth, has increased significantly in recent generations. Roughly one in three people now retain this artery throughout life, providing increased blood supply to the hand. Similarly, the decreasing frequency of wisdom teeth correlates with a trend toward smaller jaws and shorter faces in modern humans.
Infectious diseases continue to be one of the strongest evolutionary forces, driving rapid immune system changes. The sickle cell trait, a mutation that causes sickle cell anemia in homozygotes, is maintained in many populations because it confers strong resistance to malaria in heterozygotes. More recently, genetic variants that offer protection against HIV infection, specifically mutations in the CCR5 gene, have been identified.
Current Environmental Drivers of Future Evolution
The future trajectory of human evolution will be defined by the novel environments we have engineered, creating selection pressures that act on metabolic and immune function. The global trend toward urbanization is a major driver, exposing densely packed populations to novel pollutants and a higher concentration of infectious agents. This environment creates an ongoing selective pressure for robust immune responses and adaptations to chemical stressors that were not present in rural or hunter-gatherer settings.
Dietary shifts are imposing profound selective forces, characterized by readily available, high-calorie, highly processed foods. Our metabolism evolved under conditions of scarcity, favoring a “thrifty” genome that efficiently stored energy. This formerly advantageous trait is now a disadvantage, leading to a high prevalence of metabolic syndrome, obesity, and type 2 diabetes, creating a selective environment that favors genes promoting metabolic efficiency and resilience to high sugar and fat intake.
Climate change is also emerging as an undeniable selective force, particularly in regions facing extreme weather. As global temperatures rise, there may be selection for physiological traits that enhance heat tolerance, similar to the historical adaptations observed in body mass and surface area distribution along latitudinal temperature gradients. The need for adaptation to drought, altered nutrient availability, and new disease vectors driven by changing climates will continue to shape the human gene pool in coming generations.