Recent human evolution

Recent human evolution refers to evolutionary adaptation, sexual and natural selection, and genetic drift within Homo sapiens populations, since their separation and dispersal in the Middle Paleolithic about 50,000 years ago.

[6][7] With a sufficiently large data set and modern research methods, scientists can study the changes in the frequency of an allele occurring in a tiny subset of the population over a single lifetime, the shortest meaningful time scale in evolution.

[10] Human traits that emerged recently include the ability to free-dive for long periods of time,[11] adaptations for living in high altitudes where oxygen concentrations are low,[2] resistance to contagious diseases (such as malaria),[12] light skin,[13] blue eyes,[14] lactase persistence (or the ability to digest milk after weaning),[15][16] lower blood pressure and cholesterol levels,[17][18] retention of the median artery,[19] reduced prevalence of Alzheimer's disease,[8] lower susceptibility to diabetes,[20] genetic longevity,[20] shrinking brain sizes,[21][22] and changes in the timing of menarche and menopause.

[note 1] A 2017 study found correlation of Neanderthal admixture in modern European populations with traits such as skin tone, hair color, height, sleeping patterns, mood and smoking addiction.

[38][39] Victorian naturalist Charles Darwin was the first to propose the out-of-Africa hypothesis for the peopling of the world,[40] but the story of prehistoric human migration is now understood to be much more complex thanks to twenty-first-century advances in genomic sequencing.

[45][50] Moreover, a combination of gene flow from Eurasia back into Africa and higher rates of genetic drift among East Asians compared to Europeans led these human populations to diverge from one another at different times.

[dubious – discuss][citation needed] Humans dwelling in cold and dry places tend to have small, narrow, and long noses in order to warm and moisturize inhaled air.

On the other hand, tight and curly hair increases the exposed areas of the scalp, easing the evaporation of sweat and allowing heat to be radiated away while keeping itself off the neck and shoulders.

Dr. Frank Poirier, a physical anthropologist at Ohio State University, concluded that the epicanthic fold in fact may be an adaptation for tropical regions, and was already part of the natural diversity found among early modern humans.

[55][56] Physiological or phenotypical changes have been traced to Upper Paleolithic mutations, such as the East Asian variant of the EDAR gene, dated to about 35,000 years ago in Southern or Central China.

By testing the gene on mice, Yana G. Kamberov and Pardis C. Sabeti and their colleagues at the Broad Institute found that the mutated version brings thicker hair shafts, more sweat glands, and less breast tissue.

[26] Recent divergence of Eurasian lineages was sped up significantly during the Last Glacial Maximum (LGM), the Mesolithic and the Neolithic, due to increased selection pressures and founder effects associated with migration.

As this species migrated throughout Africa and began colonizing new lands outside the continent around 100,000 years ago, they came into contact with and helped spread a variety of pathogens with deadly consequences.

[5] Around 11,000 years ago, as agriculture was replacing hunting and gathering in the Middle East, people invented ways to reduce the concentrations of lactose in milk by fermenting it to make yogurt and cheese.

[15] Today, lactase persistence can be found in 90% or more of the populations in Northwestern and Northern Central Europe, and in pockets of Western and Southeastern Africa, Saudi Arabia, and South Asia.

[79][80][75] A research program by geneticist Hans Eiberg and his team at the University of Copenhagen from the 1990s to 2000s investigating the origins of blue eyes revealed that a mutation in the gene OCA2 is responsible for this trait.

A study of ancient DNA estimated nature, strength, and time of onset of selections due to pathogens and also found that "the bulk of genetic adaptation occurred after the start of the Bronze Age, <4,500 years ago".

Armed with this technique and data from the UK10K project, Pritchard and his team found that alleles for lactase persistence, blond hair, and blue eyes have spread rapidly among Britons within the last two millennia or so.

The technique also enabled them to track the selection of polygenic traits—those affected by a multitude of genes, rather than just one—such as height, infant head circumferences, and female hip sizes (crucial for giving birth).

[92] A study published in 2021 states that the populations of the Cape Verde islands off the coast of West Africa have speedily evolved resistance to malaria within roughly the last 20 generations, since the start of human habitation there.

[96] For a long time, medicine has reduced the fatality of genetic defects and contagious diseases, allowing more and more humans to survive and reproduce, but it has also enabled maladaptive traits that would otherwise be culled to accumulate in the gene pool.

Moreover, while the introduction of antibiotics initially reduced the mortality rates due to infectious diseases by significant amounts, overuse has led to the rise of antibiotic-resistant strains of bacteria, making many illnesses major causes of death once again.

[98] Among developed countries, where life expectancy is high and infant mortality rates are low, selective pressures are the strongest on traits that influence the number of children a human has.

This evolutionary tug-of-war attained an equilibrium, making these traits remain more or less constant over time while allowing for genetic variation to flourish, thus paving the way for rapid evolution should selective forces shift their direction.

Daghni Rajasingam of the Royal College of Obstetricians observed that the increasing rates of diabetes and obesity among women of reproductive age also boost the demand for C-sections.

Pickrell and Przeworski told The Atlantic that a sample of half a million individuals would enable them to study mutations that occur among only 2% of the population, which would provide finer details of recent human evolution.

[8] While studies of short time scales such as these are vulnerable to random statistical fluctuations, they can improve understanding of the factors that affect survival and reproduction among contemporary human populations.

[10] A 2017 study by researchers from Northwestern University unveiled a mutation among the Old Order Amish living in Berne, Indiana, that suppressed their chances of having diabetes and extends their life expectancy by about ten years on average.

That mutation occurred in the gene called Serpine1, which codes for the production of the protein PAI-1 (plasminogen activator inhibitor), which regulates blood clotting and plays a role in the aging process.

Allergies, asthma, and autoimmune disorders appear linked to higher standards of sanitation, which prevent the immune systems of modern humans from being exposed to various parasites and pathogens the way their ancestors' were, making them hypersensitive and more likely to overreact.