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Famine and disease drove the evolution of lactose tolerance in Europe

2022年7月27日

Prehistoric people in Europe were consuming milk thousands of years before humans evolved the genetic trait allowing us to digest the milk sugar lactose as adults, finds a new study led by UCL and University of Bristol researchers.

牛奶

这项研究发表在 自然, mapped pre-historic patterns of milk use over the last 9,000年, offering new insights into milk consumption and the evolution of lactose tolerance.

直到现在, it was widely assumed that lactose tolerance emerged because it allowed people to consume more milk and dairy products. But this new research shows that famine and exposure to infectious disease best explain the evolution of our ability to consume milk and other non-fermented dairy products.

Joint senior author Professor Mark Thomas (彩票购买的遗传学,进化 & 环境)说:“在史前晚期, as our ancestors started living in larger settlements, their health was increasingly impacted by poor sanitation and increased pathogen loads. 在这种情况下, 在饥荒时期更是如此, 喝牛奶会增加死亡率, particularly among those unable to digest the lactose in milk. Those who were able to digest lactose were thus more likely to pass on their genes enabling them to safely drink milk.”

While most European adults today can drink milk without discomfort, 今天世界上三分之二的成年人, 和几乎所有的成年人,000年前, 喝太多牛奶会有问题吗. 这是因为牛奶含有乳糖, 如果彩票购买平台不消化这种独特的糖, it will travel to our large intestine where it can cause cramps, 腹泻, and flatulence; known as lactose intolerance. 然而, this new research suggests that in the UK today these effects are rare.

乔治·戴维·史密斯教授, Director of the MRC Integrative Epidemiology Unit at the University of Bristol and a co-author of the study, said: “To digest lactose we need to produce the enzyme lactase in our gut. 几乎所有的婴儿都会产生乳糖酶, but in the majority of people globally that production declines rapidly between weaning and adolescence. 然而, a genetic trait called lactase persistence has evolved multiple times over the last 10,000年 and spread in various milk-drinking populations in Europe, 中亚和南亚, 中东和非洲. Today, around one third of adults in the world are lactase persistent.”

通过绘制过去9年里牛奶的使用模式,000年, 调查英国生物银行, 结合古代DNA, 放射性碳测定年代, and archaeological data using new computer modelling techniques, the team were able to show that the lactase persistence genetic trait was not common until around 1,000 BC, 近4,大约在4年前首次被发现,700–4,600 BC.

Professor Thomas added: “The lactase persistence genetic variant was pushed to high frequency by some sort of turbocharged natural selection. The problem is, such strong natural selection is hard to explain.”

In order to establish how lactose persistence evolved, 教授理查德·埃弗利谢德, 这项研究的负责人来自布里斯托尔化学学院, 建立了一个前所未有的近7人的数据库,000 organic animal fat residues from fragments of pottery from 554 archaeological sites to find out where and when people were consuming milk. His findings showed milk was used extensively in European prehistory, 最早可追溯到近9年的农耕时代,000年前, but increased and decreased in different regions at different times.

To understand how this relates to the evolution of lactase persistence, 彩票购买的团队, 由托马斯教授领导, assembled a database of the presence or absence of the lactase persistence genetic variant using published ancient DNA sequences from more than 1,700个史前欧洲和亚洲个体. 他们第一次看到它是在大约5000年前. By 3,000年前 it was at appreciable frequencies and is very common today. 下一个, his team developed a new statistical approach to examine how well changes in milk use through time explain the natural selection for lactase persistence. 令人惊讶的是, 他们没有发现任何关系, even though they were able to show they could detect that relationship if it existed, challenging the long-held view the extent of milk use drove lactase persistence evolution. 

Professor Davey Smith’s team had been 调查英国生物银行 data, 其中包括300多个基因和医学数据,000个人, and found only minimal differences in milk drinking behaviour between genetically lactase persistent and non-persistent people. 批判性的, the large majority of people who were genetically lactase non-persistent experienced no short or long-term negative health effects when they consume milk.

Professor Davey Smith added: “Our findings show milk use was widespread in Europe for at least 9,000年, 和健康的人类, 即使是那些乳糖不耐受的人, 能快乐地喝牛奶而不生病吗. 然而, drinking milk in lactase non-persistent individuals does lead to a high concentration of lactose in the intestine, 能把液体吸进结肠, and dehydration can result when this is combined with 腹泻l disease.

与此同时, Professor Thomas had been thinking along related lines, 但更强调史前的饥荒. He reasoned: “If you are healthy and lactase non-persistent, 你喝很多牛奶, 你可能会感到不舒服, 但你不会因此而死. 然而, 如果你严重营养不良并腹泻, 然后你就有了危及生命的问题. 当他们的庄稼歉收时, prehistoric people would have been more likely to consume unfermented high-lactose milk – exactly when they shouldn’t.”

为了验证这些观点, Professor Thomas’ team applied indicators of past famine and pathogen exposure into their statistical models. Their results clearly supported both explanations – the lactase persistence gene variant was under stronger natural selection when there were indications of more famine and more pathogens.

这项研究的合作者来自21个国家, 并得到了英国皇家学会的资助, 医学研究理事会(MRC), 自然环境研究委员会, 和欧洲研究理事会.

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