Scientists say that those who go to bed early and wake up early may owe this behavior to their ancient ancestors. Researchers found that the DNA inherited from our thick-browed relatives may contribute to some people's tendency to be early risers more than others. While most genes acquired by modern humans through ancient hybridization have been eliminated through evolution, a small portion remains, likely because it helped early contemporary humans adapt to their new environment as they left Africa for Eurasia.
Between 60,000 and 70,000 years ago, our ancestors were migrating out of Africa to Europe, where they encountered Neanderthals and Denisovans, with whom we share 93% of our DNA. New research suggests that the three groups interbred and transferred genes that helped subsequent generations adapt to the northern climate and sunlight. Among these genetic variants are those known to be associated with "waking up early," including those that specifically regulate our circadian rhythms and sleep-wake cycles. Therefore, if you tend to wake up early in the morning, this may be the reason.
To understand the impact of ancient genes in modern times, a team of scientists from Vanderbilt University, the University of Pennsylvania, and the University of California in San Francisco examined genetic data from a catalog of hundreds of thousands of people in the UK. They conducted a genome-wide association study (GWAS) to search for traits associated with early rising. The GWAS looks at genetic variants statistically associated with people's traits. In the past, GWAS has been responsible for identifying genes that increase individuals' risk of diseases such as kidney disease or insomnia.
They compared these associations with the genomes derived from three ancient hominins: a 120,000-year-old Neanderthal, a 72,000-year-old Denisovan found in the mountains of Mongolia, and a 52,000-year-old Neanderthal from modern times discovered in Croatia. Sixteen different types of genes associated with higher levels of "early rising" in modern humans were woven into the DNA fabric of ancient hominins. Among these genes are "clock genes" that specifically help regulate our biological rhythms. It has long been suspected that the mixing of DNA between modern human ancestors and hominins transferred certain tendencies to their descendants.
Scientists believe that these adaptations may have helped them adjust to the transition to northern latitudes. Compared to Africa, Europe and Asia had greater seasonal differences in weather and sunlight. The genes identified in the new study may have helped them survive during the relatively shorter days. The study suggests that a shorter biological period helps individuals adapt to rapidly changing conditions.
