A recent study has unveiled fascinating insights into the genetic makeup of East Asian populations, revealing that unique versions of the lactase gene—enabling the digestion of milk sugars—may have a deeper evolutionary significance. These genetic variants, likely inherited from Neanderthals, have been found to bolster immune responses against pathogens, potentially offering a survival advantage to ancient hunter-gatherers. The study, comparing thousands of genomes from modern humans across various continents, suggests that these lactase gene variants began to be selected for between 25,000 and 28,000 years ago, long before the emergence of dairy culture in the Altai Mountains.
A large proportion of East Asian people possess these distinct lactase gene variants, which differ significantly from those found in European and African populations. The research indicates that about 25% of individuals with East Asian ancestry carry these versions, reflecting a similar proportion to those who exhibit lactase persistence in this demographic. Intriguingly, while approximately 65% of adults worldwide are lactose intolerant, this figure escalates to between 70% and 100% among East Asian populations.
The origins of these variations trace back tens of thousands of years. Neanderthals, who roamed Eurasia for roughly 400,000 years, interbred with Homo sapiens on multiple occasions. This genetic mingling likely transferred alleles adapted to local pathogens and environmental challenges to human ancestors. Shuhua Xu, a professor of human population genetics at Fudan University in China, notes:
"Neanderthals — having inhabited Eurasia for approximately 400,000 years — likely carried alleles [genetic variants] adapted to local pathogens and environmental challenges."
The study's authors propose that the integration of these Neanderthal alleles may have conferred an enhanced ability to combat infections among East Asian hunter-gatherers. By altering the activity of three genes in immune cells, these lactase gene variants potentially increased immune cell numbers, providing a crucial advantage in ancient environments rife with pathogens.
The comparative analysis included samples from diverse countries such as China, Japan, Spain, Italy, and Nigeria. Researchers drew parallels between East Asian genomes and that of a Neanderthal who lived in Siberia's Altai Mountains around 120,000 years ago. This comparative approach underscored the uniqueness of the East Asian lactase gene variants, which do not appear within European or African populations.
Historically, the versions of the lactase gene linked to lactase persistence are believed to have emerged in Europe and Africa between 5,000 and 10,000 years ago. However, the recent findings suggest that lactose-intolerance variants within East Asians were being selected for significantly earlier—over 10,000 years before dairy practices became commonplace in the Altai Mountain region.
This research sheds light on the complex evolutionary history shared by humans and their extinct Neanderthal cousins. It suggests that genetic traits advantageous for survival in ancient times continue to influence modern populations in significant ways. The persistence of these lactase gene variants among East Asians today underscores their enduring evolutionary legacy.
