Sweet and tasty milk is a poison for former adults?

Milk, not just drink on

During the recent ice age, milk was poison for adults. Unlike children, adults were unable to produce lactase to break down lactose, the main sugar in milk. But in the Middle East about 11,000 years ago, as farming gradually replaced hunting and gathering, cattle farmers learned to ferment milk to make cheese or yogurt, which reduced the lactose in dairy products to levels that humans could tolerate. After a few thousand more years, a genetic mutation spread throughout Europe that enabled humans to produce lactase and thus drink milk for a lifetime. This developed a whole new source of rich nutrition for humans, allowing them to survive the lean years.

The milk revolution had a profound impact on the development and settlement of the European continent. It was probably the main reason why farmers and herders in southern Europe were able to sweep across the continent and replace the hunter-gatherer culture that had existed here for thousands of years. From an archaeological point of view, they spread quite rapidly. This wave of migration left a permanent mark on Europe - unlike many parts of the world, most of its people are now lactose tolerant. Scientists believe that most Europeans are probably descended from the first European farmers with lactose tolerance.

The genetic mutation that allows humans to drink milk

Young children can almost always produce the enzyme lactase, which breaks down the lactose in breast milk. But as they mature, the lactase gene is turned off in most people. Most people who retain the ability to drink milk can trace their lineage back to Europe. Lactose tolerance in Europeans appears to be associated with a single nucleotide mutation from cytosine to thymine near the lactase gene.

This mutation occurred relatively late. Looking at the genetic diversity of modern humans and using computer simulations of how the mutation spread in ancient populations, the scientists finally estimated that the lactose tolerance allele appeared in Hungary about 7,500 years ago.

The emergence of lactose tolerance genes provides a huge evolutionary advantage. In a 2004 study, scientists estimated that individuals with the mutation produced 19% more fertile offspring than those without the mutation, a huge advantage that ranks among the highest in the entire genome.

This advantage was passed on for hundreds of generations, helping a group of people take over a large continent. However, scientists believe that this advantage only comes into play when the population has a source of fresh milk and ingests dairy. It is a process of genetic and cultural co-evolution, and the two are interdependent.

Milk unravels the mystery of European origins

By studying human molecular biology and archaeology and chemistry of ancient pottery, scientists hope not only to find out the history of the interplay between genes and culture, but also to clarify a key question about the origins of modern Europeans, a long-standing archaeological question - whether they replaced native populations by their superiority descendants of Middle Eastern farmers, or were they the descendants of native hunter-gatherers?

Based on animal bone studies, scientists have suggested that the dairy industry in the Middle East may date back to the first domestication of animals by humans, 10,500 years ago. This was just after the Neolithic Revolution began in the Middle East - when the economic model shifted from hunter-gatherer to agriculture. Access to dairy products may have been one of the reasons humans began capturing and raising cattle, sheep, and goats as ruminants.

The dairy industry then spread along with the Neolithic Revolution. Agriculture spread from Anatolia to northern Europe over the next 2,000 years, and the spread of dairy farming followed this pattern. Analyzing the pattern of dairy development alone does not indicate whether the Neolithic Revolution spread in Europe by way of evolution or substitution, but cattle bones provide important clues to this question. Scientists have found that domestic cattle from Neolithic sites in Europe are most closely related to cattle from the Middle East and more distantly related to the native European bison. Studies of ancient human DNA from several sites in Central Europe have come to similar conclusions. This suggests that Neolithic farmers were not descended from indigenous hunter-gatherers.

Given that dairy farming emerged in the Middle East thousands of years before the emergence of lactose tolerance genes in Europe, ancient graziers must have found a way to reduce the lactose content of milk. At present, it seems likely that they resorted to making milk into cheese or yogurt.

To test this theory, scientists have conducted chemical tests on ancient pottery. These tests were able to measure whether the residual lipids originated from meat or milk, from ruminants or other animals.

They found milk fat on pottery at least 8,500 years old from the Fertile Crescent in the Middle East, and in 2011, several Stone Age pottery sherds from Poland, which were used by early farmers as sieves for making cheese, were also found to contain high levels of milk fat. The pottery suggests that European graziers were already making cheese between 6,800 and 7,400 years ago. By then, dairy products had become part of the Neolithic recipes, but not yet an important part of the economy.

Making milk available to more Europeans

Humans entered a second stage in their relationship with milk - direct consumption. This stage progressed more slowly and appears to have required the widespread spread of lactose tolerance as a foundation. After the emergence of the lactose tolerance gene, it took some time before it became widespread in the population. Scientists studied mutations in ancient human DNA samples and found that such mutations appeared in northern Germany 6,500 years ago.

Population geneticists explain that this trait may have entered Europe with the Neolithic cultures of the Middle East, whose farming and herding techniques made them competitive with local hunter-gatherers. As people in southern Europe pushed northward, lactose tolerance genes rode on the east wind of this human migration.

The spread of lactose tolerance in southern Europe was not so easy, as Neolithic farmers were already settled here long before this mutation appeared. But as agricultural societies advanced north and west, the advantages offered by lactose tolerance had a dramatic impact, and the rapid growth of migrating populations led to an increase in the gene frequency of lactose tolerance genes.

To date, lactose tolerance is still relatively rare in southern Europe

This pattern of expansion is still evident today. In southern Europe, lactose tolerance is relatively rare - less than 40% in the Greek and Turkish populations. But in Britain and Scandinavia, more than 90% of adults can digest milk.

By the Late Neolithic and Early Bronze Age, about 5,000 years ago, lactose tolerance genes were widespread in much of northern and central Europe, and cattle ranching had taken a major role in the culture. In many late Neolithic and early Bronze Age sites in central and northern Europe, cattle bones make up more than two-thirds of animal bones.

Why would being able to drink milk be an advantage?

What still puzzles scientists, however, is how the ability to ingest milk in these regions could have brought such an advantage. It has been suggested that as people migrated north, the intake of milk became a powerful means of staving off famine. Dairy products can be preserved longer in colder places and provide people with an abundance of calories regardless of seasonal changes, or good or bad harvests.

It is also thought that it may be because milk is richer in vitamin D, which helps people prevent diseases like rickets. This one advantage is especially evident in the north, where humans can only synthesize vitamin D when exposed to sunlight, and for northerners, it is difficult to get enough sunlight in the winter. However, lactose tolerance is also prevalent in sunny Spain, which leaves the vitamin D theory in doubt.

In this study scientists set an example that archaeological questions can also be answered with knowledge and tools from many different fields, combining the power of archaeology, paleoanthropology, ancient and modern DNA, and chemical analysis to solve a problem. There are also many questions related to dietary changes, such as the origin of amylase and ethanol dehydrogenase. This study may also provide an idea and direction for them.