The last Ice Age, about 11,500 to 21,000 years ago, was a cool period characterized by a series of changes for life on Earth. Early humans survived these changes and evolved into today's Homo sapiens, but according to a new study, a rare genetic mutation secretly could have played a crucial role in this transformation.
About 20,000 years ago, when the Glacial period just started to peak, Native Americans and East Asians experienced very low levels of UV radiation from the sun. This, according to the study, disrupted vitamin D production in neonatal skin and impaired its growth and survival, but the mutation compensated for the effect and helped the baby grow and thrive.
Essentially, the genetic changes increased the density of branching of mammary glands in the breasts, helping mothers to deliver enough vitamin D and fat to their infants through lactation.
"This highlights the importance of the mother-child relationship and how important it was to human survival," explains Leslea Hlusko Professor of Integrative Biology at the University of California, Berkeley, said in a statement.
People living near the equator receive enough vitamin D for fat regulation and calcium absorption, but those in high latitudes miss it because the sun is not shining. They shine all year long. To address this, people dealt with fat-chasing centuries ago, but babies relied exclusively on breastfeeding.
Interesting is also the fact that the rare mutation had an influence on the shape of the teeth of the population. The researchers noticed at approximately the same time as the mutation was spreading, Indians and Northeast Asians began to develop scoop-shaped incisors (with burrs on the sides and biting edge), something found only in humans of the two groups. The change in the shape of the teeth and the branching of the ducts are linked to the same gene in humans.
Hlusko and colleagues postulated this theory after studying population records. In fact, they found that nearly 100 percent of the early Native Americans and 40 percent of today's East Asians had scoop-shaped incisors at that time. Then they used the genetic effect associated with dental variation to understand the development of mammary glands during the last ice age.
Previous studies have suggested that scoop-shaped incisors have developed as a means of softening the animal's skin, but the new theory
"People have long believed that this scoop pattern is so strong that there has been evolutionary selection which favors the feature, but why should there be such a strong selection on the shape of your incisors? " Hlusko added. "When you've spread genetic effects across the body, selecting one feature will make sure everything else goes with you."
The team hopes ultimately that the information from this work can be used to understand the origins of dense breast tissue and the role it plays in breast cancer
The study titled "Environmental Selection during the Last Glacial Period in the Mother "Child Transmission of Vitamin D and Fatty Acids by Breastmilk" was published on April 23 in Proceedings of the National Academy of Sciences.