According to a new study, people that were alive during the last ice age may have been helped along the way by a genetic mutation that ensured their survival.
This genetic mutation, common to both North Americans and East Asians, is directly tied to breastfeeding and vitamin D intake and seems to have occurred some 20,000 years ago, when early Native Americans first came to Beringia, the now-submerged land between Asia and Alaska, Science Magazine reports.
The discovery was made by researchers at the University of California, Berkeley, who note that the gene in question, called EDAR, may have helped the ancestors of Asians and Native Americans adapt to the cold, long winters towards the end of the ice age and make up for the scarcity of sunlight that they were facing after migrating so far north.
Scarcity of ultraviolet light inhibits the production of vitamin D in the skin, important for fat regulation and calcium absorption. This would have triggered a set of health problems for these ancient tribes, but the ancestral populations managed to thrive by hunting large animals for their fat.
Babies, however, relied solely on breast milk for nutrients, notes International Business Times. And this is where the genetic mutation came in. A variant of the EDAR gene, called V370A, evolved to help nursing mothers pass on more fat and vitamin D to their babies, by branching the density of mammary ducts in the breasts, explains a UC Berkeley news release.
"This highlights the importance of the mother-infant relationship and how essential it has been for human survival," study author Leslea Hlusko, a biological anthropologist from UC Berkeley, states in the news release.This adaptation was so beneficial that the EDAR V370A variant eventually spread to everyone in the Americas, notes the Berkeley study, published yesterday in the journal Proceedings of the National Academy of Sciences.
The team managed to track down EDAR V370A because of the way this genetic mutation changed the shape of teeth. In turns out that "the gene controlling mammary duct growth also affects the shape of human incisors," giving them a shoveled form, details the news release.
The study provides evidence that Native Americans and Asians living in the north-east all share the genetic trait of shoveled-shaped incisors, which is seldom seen in the rest of the populations. The researchers believe that explanation may lie in the genetic makeup of early Native Americans, who spread the gene to other populations after their arrival in Beringia.Hlusko's team backs up their theory by pointing to fossil records. The scientists examined data on the teeth of more than 5,000 people from 54 archaeological sites in Europe, Asia, and North and South America. They discovered that all the Native American fossils, 3.183 in total, had shoveled teeth, meaning the all carried the EDAR V370A variant that caused the mutation. The same genetic mutation was also found in 40 percent of the Asian fossils, which records showed also had shoveled-shaped incisors.
"People have long thought that this shoveling pattern is so strong that there must have been evolutionary selection favoring the trait, but why would there be such strong selection on the shape of your incisors?" Hlusko pointed out.
"When you have shared genetic effects across the body, selection for one trait will result in everything else going along for the ride," she added.