Breastfeeding has always been critical for healthy infants, but even more so many years ago – it was an essential part of infant survival. However, during the last ice age it could have led to changes in tooth shape in pre-Native Americans. A new study suggests that pre-Native Americans had to adjust to the life conditions in the North where there is very little sunlight at times. That caused them to develop a mutation that helped them acquire sufficient amounts of vitamin D and fats through breastfeeding.
The genetic mutation in tooth shape in pre-Native Americans and East Asians likely occurred about 20,000 years ago, and it also “increased branching density of mammary ducts in the breasts, potentially providing more fat and vitamin D to infants living in the far north.” The lack of sun and ultraviolet radiation made it hard to produce enough vitamin D in the skin.
“This highlights the importance of the mother-infant relationship and how essential it has been for human survival,” Leslea Hlusko, an associate professor of integrative biology at the University of California, Berkeley said in a statement.
Hlusko and her team published their findings and evidence of their idea in the journal Proceedings of the National Academy of Sciences. Scientists also noted that the findings of this study could shed light on the origin of dense breast tissue and its possible role in breast cancer.
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In the study, Hlusko and her team looked at the occurrence of shovel-shaped incisors in archaeological populations so that they could determine the time and place when the mutation in tooth shape in pre-Native Americans occurred. Almost 100% of Native Americans, before the Europeans migrated west, had shoveled incisors. Additionally, 40% of East Asians today have shoveled incisors as well.
After that, the team referred to the genetic effects that are shared with the different dental variations to ascertain the evolutionary history of mammary glands due to its known developmental pathway.
“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 said. “When you have shared genetic effects across the body, selection for one trait will result in everything else going along for the ride.”
Vitamin D is essential to every immune system and it helps regulate fat throughout the body, and as well it is essential for calcium absorption. However, getting proper amounts of vitamin D is difficult in the north where the sun is low on the horizon all year round. Moreover, above the Arctic Circle, there is no sun at all for a part of the year.
Hlusko, who specializes in the evolution of teeth among animals, discovered the connections between getting enough vitamin D and tooth shape in pre-Native Americans. She made this discovery after being asked to take part in a scientific event on the dispersal of modern humans at the February 2017 American Association for the Advancement of Science meeting.
According to the study, these “shovel-shaped” incisors are present in Native Americans and people who live in East Asia. They can be found in Korea, Japan and northern China. The incidence of finding shovel-shaped incisors, the cutting teeth in the front of the mouth, four on top and four on the bottom, with ridges on the side of the teeth and on the biting edge, increases towards the North.
Hlusko discovered that the genetic mutation for the shoveled incisors is the same one that determines the density of sweat glands in the skin and ductal branching in mammary gland. More study is planned to discover more about the mutation.