An analysis of ancient human DNA by scientists tracked the changes in DNA from when humans transitioned from a hunter-gatherer species to a farming one. The findings show that changes in diet, in addition to the new habitat landscapes, are associated with genes that account for height, vitamin D levels, and others.
The Neolithic era was marked by advancement in technological tools and human culture. During this period, demographically speaking, early humans lived close together in larger numbers and had started developing agricultural acumen.
With the development of farming around 8,500 years ago, our early ancestors were exposed to new environmental landscapes, diets, and social structures. The gradual shift from a hunter-gatherer lifestyle to a farming one was marked by adaptation and genetic variation among the participating populations. These genetic variations provide clues and patterns about the history of human evolution and expansion during the transition.
Until now, it had been difficult to follow the patterns and trace the transformation of human DNA due to low sample sizes of available ancient DNA. However, a research team combining members from Harvard Medical School and University College Dublin were able to conduct a large genome-wide scan that contained ancient DNA from 230 West Eurasians living between 6500 and 300 BC. Their data set included the first ancient DNA of Anatolian (in what is now Turkey) Neolithic farmers using DNA from the inner ear.
The objective of the study was to chronologically document the genetic changes from hunting-gathering to farming and to associates these changes with environmental ones during human expansion by farmers.
First, their findings provided insight into the expansion of early humans. They found that the Anatolian Neolithic samples were closer to early European farmers from Germany, Hungary, and Spain than to any present-day near-Eastern populations. These findings corroborate the previously believed hypothesis amongst scholars that Europe’s first farmers came from ancient Anatolia before further expanding throughout modern day Europe.
As humans expanded towards Europe after the transition towards farming, their farming techniques were brought along with them.
When the researchers compared the ancient DNA to one another and to those of present-day Europeans, they found that many of the variants in DNA were related to genes that were associated with, for example, height, ability to digest lactose, vitamin D levels, and lighter skin pigmentation.
In the instance of height, the team found a significant directional selection; that is, there existed a South—North gradient in height increase across Europe.
Samples from the Iberian Neolithic era, where the Iberian Peninsula of Southwestern Europe (occupied by Spain and Portugal) demonstrated selection for reduced height relative to the Anatolian Neolithic era samples. Increased height was found among Eurasian populations that lived in steppes, which are characterized by flat grasslands.
Due to the complexity of genes regulating height, it is difficult to pinpoint the observed phenomenon by the researchers. It is proposed that in southern Europe people grew shorter after the introduction of farming. It is proposed that an indirect consequence of agriculture and the reliance on grain may have posed a risk for missing out on other important nutrients.
The reduced intake of vitamin D with the advent of agriculture is hypothesized to play a role in lighter skin pigmentation expression. Very foods naturally contain vitamin D and a paler complexion would favour vitamin D absorption from the sun in higher latitudes, like northern Europe.
Other findings included a gene which allowed for increased absorption of a protein found in grains by humans and that its variant was responsible for raising the risk of digestive disorders like irritable bowel disease.
Despite the complexity of human evolution, the research team was successful at demonstrating that the transition from a hunter-gatherer lifestyle to an agricultural one was a factor in influencing biology. With more DNA samples, researchers in the future can compare DNA changes outside of European populations to trace genetic variation and selection more precisely.