Female mammals produce milk to nourish their young people. Most of the nutrients come from lactose, the main sugar in milk. Lactose is broken down into simpler sugars, glucose and galactose in the baby’s small intestine, which are easily absorbed by the small intestine. The breakdown or digestion of lactose is mediated by an enzyme called lactase.
After weaning, the baby quickly loses the ability to produce lactase. When adults consume milk, cheese, ice cream or other dairy products, many of them experience unpleasant effects such as bloating, flatulence, and diarrhea. This is because uneliminated lactose enters the large intestine, where it is exploited by the bacteria that live there. This produces hydrogen, carbon dioxide and methane, and unabsorbed sugar increases the flow of water into the intestines to produce diarrhea. These are signs of lactose intolerance.
Even for adults, however, millions of people around the world often indulge in milkshakes, cheese pizza and ice cream sundaes. This is because they have genetic mutations that can continue to produce lactase even in adults. This feature is called lactase persistence.
Textbook examples
Mutations conferring persistent lactase occur independently in different populations. Their appearance in the Nordic and African populations seemed to coincide with the domestication of cattle, buffalo, goats, sheep and other livestock about 11,000 years ago. The cultural shift from hunting/gathering to herders has made feeding animals constantly gained by meat, milk and leather.
At that time, many scientists described the coincidence of persistent mutations in lactase and domestication of livestock as “textbook examples” of fusion evolution. That is, the independent evolution of similar traits in distantly relevant populations. Experts believe that Papers in 2007 exist Natural Geneticsthrough “strong selective pressures generated by common cultural characteristics – animal domestication and adult milk consumption”.
Wrinkles in textbooks
Scientists may need to reevaluate this neat summary based on new findings reported by a team of researchers at Fudan University in Shanghai, China; the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany; and the University of Delion in France. Their discovery Published exist Proceedings of the National Academy of Sciences.
The researchers found a unique evolutionary pathway for the persistence of lactase in East Asian populations, including China, Japan and Vietnam. Unlike well-documented genes and cultural co-evolution in African and European populations, East Asian lactase persistent genes are derived from Neanderthals, an ancient human, about 30,000 years ago.
When the researchers performed population genetic analysis of the portion of the genome containing the lactase gene, they found evidence of pre-agricultural selection pressures that began 30,000 years ago. That is, before these populations began to domesticate livestock, the East Asian genome began to develop lastingly towards lactase.
This early evolution may target advantages related to the immune system rather than directly digesting lactose. The researchers found that the expression pattern of East Asian (Neanderthal-derived) lactase genes was the same as the mutant responsible for the persistence of European human lactase. This also shows that it also confers lactic acid durability.
Neanderthals in our genome
About 7 million years ago, evolutionary lines led to the contemporary Homo sapiens Differences with the one who led our closest cousin, the chimpanzee and the bob. About 800,000 years ago, our production line split again: a population collapsed and moved to Eurasia, adapted to the cold climate, and eventually became Neanderthal. The other one stayed in Africa, and by about 200,000 years ago, had evolved into modern humanity.
Modern humans migrated from Africa to Eurasia 120,000 to 80,000 years ago and contacted Neanderthal cousins there. After contact, the DNA evidence of the bones can still date to occasionally date each other. As a result, today, about 1-4% of individuals of Eurasian descent (i.e., Europeans, East Asian, Indians, Native Americans and Oceanians) represent Neanderthal-derived DNA sequences. This is the part of the lactase gene in East Asians. On the other hand, the sequence of African descent is close to Neanderthal-derived sequences.
About 30,000 years ago, the Neanderthals became extinct for reasons that are not yet known.
Bones selection
Experts can distinguish Neanderthal skeletal residues from modern human relics by skull, inner ear bones and pelvic width. Neanderthal bones produce DNA, scientists sequenced it and compared it with H. Sapiens.
The DNA sequences of the two random populations were about 99.9%, while humans and Neanderthals had only about 99.7%. Therefore, in terms of the bases of DNA, the difference between Neanderthal and human DNA sequences is about 9.6 million. Based on these differences, if the DNA sequence is long enough, it can be distinguished whether it is from a human or a Neanderthal.
this Alan Ancient DNA Resources (AADR) is a curated database of over 10,000 genomic sequences derived from skeletal remains of ancient individuals whose lives lasted 20,000 years ago. The researchers who put this resource together also determined that on each genome, the base of the known DNA has shown a different base sort compared to “normal”.
About 67% of the ancient DNA sequences in the AADR come from remains in Europe and Russia, each from about 8% from East and Near East, about 7% from the Americas, about 5% from South and Central Asia, about 3% from Africa, and about 2% from Oceania.
A story has been subverted
The researchers behind the new study searched AADR and discovered a modern human who lived in the Amur region of China 14,000 years ago. This person carries a Neanderthal-derived lactase gene. The gene occurs in about 10% of people 8,000 to 3,000 years ago, and about 20% of people 3,000 to 1,000 years ago. It currently has a frequency of 28.9% among East Asians.
Therefore, the AADR data also support the inference of population genetic analysis: the lactase gene has undergone selection and has reached (relatively) high frequency in East Asians before East Asians began domesticating animals.
Therefore, unlike Africans and Nordics, East Asians’ choices are for reasons other than lactase persistence, or in these three geographical locations, the choices are also not for lactase persistence.
Either way, given these findings, the classic story of gene-cultural co-evolution has become more complex, and therefore, as the researchers point out, is more interesting.
DP Kasbekar is a retired scientist.
publishing – May 13, 2025 at 05:30 AM IST
