The extraction and analysis of milk-specific proteins from ancient materials, including dental calculus, has allowed scientists to uncover the origins of dairying in Eastern Africa.

Some 6,000 years ago, toothbrush technology was non-existent. As a result, the teeth of early humans accumulated significant amounts of plaque. These mineralized layers of ancient plaque, hardened by time, form what's called calculus.

A new survey of calculus content collected from 41 adult individuals, excavated from 13 ancient pastoralist sites in Sudan and Kenya, turned up several milk-specific proteins -- evidence of early milk consumption.

Researchers shared the results of the survey in a new paper, published Wednesday in the journal Nature Communications.

"Some of the proteins were so well preserved, it was possible to determine what species of animal the milk had come from," lead author Madeleine Bleasdale said in a news release.

"And some of the dairy proteins were many thousands of years old, pointing to a long history of milk drinking in the continent," said Bleasdale, a researcher at the Max Planck Institute for the Science of Human History in Germany.

Researchers identified evidence of milk consumption in the dental calculus of eight individuals, the earliest of which was recovered in Sudan and dated to 6,000 yeas ago.

"This is the earliest direct evidence to date for the consumption of goat's milk in Africa," said Bleasdale. "It's likely goats and sheep were important sources of milk for early herding communities in more arid environments."

Researchers also found milk proteins preserved in the dental calculus of an individual buried at a herder settlement site in southern Kenya, dated to between 3,600 and 3,200 years ago.

"It seems that animal milk consumption was potentially a key part of what enabled the success and long-term resilience of African pastoralists," said Steven Goldstein, study co-author and Max Planck researcher.

The latest findings suggest the development of dairy consumption in early African populations drove the evolution of human biology and the emergence of lactase persistence.

Lactase is the enzyme that allows humans to breakdown and fully digest lactose. In most people, lactase production tapers off after childhood, though it does persist in some.

Among European populations, a single genetic mutation is responsible for lactase persistence, but in Africa, lactase persistence has been linked with several different gene mutations.

Through genetic analysis, researchers were able to confirm that the milk drinkers unearthed in Sudan and Kenya were without the genes for lactase persistence. In other words, milk consumption predates the emergence of lactose tolerance.

The findings suggest human dairy consumption actually triggered the emergence and spread of lactase gene mutations, and that Africa was a key site for this evolutionary phenomena.

Scientists suspect fermentation likely helped early African herders digest milk. Fermented milk products, like yogurt, have lower levels of lactose, making it easier to digest.

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