Prehistoric alarms: Morning person? Thank your Neanderthal genes

NEW YORK: Neanderthals were morning people, a new study suggests. And some humans today who like getting up early might credit genes they inherited from their Neanderthal ancestors. The new study compared DNA in living humans with genetic material retrieved from Neanderthal fossils.

Neanderthals carried some of the same clock-related genetic variants as do people who report being early risers.

Since the 1990s, studies of Neanderthal DNA have exposed our species’ intertwined history.

About 700,000 years ago, our lineages split apart, most likely in Africa. While the ancestors of modern humans largely stayed in Africa, the Neanderthal lineage migrated into Eurasia. About 400,000 years ago, the population split in two. The hominins who spread west became Neanderthals.

Their cousins to the east evolved into a group known as Denisovans.

The two groups lived for hundreds of thousands of years, hunting game and gathering plants, before disappearing from the fossil record about 40,000 years ago.

By then, modern humans had expanded out of Africa, sometimes interbreeding with Neanderthals and Denisovans. And today, fragments of their DNA can be found in most living humans.

Research carried out over the past few years by John Capra, a geneticist at the University of California, San Francisco, and other scientists suggested that some of those genes passed on a survival advantage. Immune genes inherited from Neanderthals and Denisovans, for example, might have protected them from new pathogens they had not encountered in Africa.

Dr. Capra and his colleagues were intrigued to find that some of the genes from Neanderthals and Denisovans that became more common over generations were related to sleep.

For their new study, published in the journal Genome Biology and Evolution, they investigated how these genes might have influenced the daily rhythms of the extinct hominins.

Inside the cells of every species of animal, hundreds of proteins react with each other over the course of each day, rising and falling in a 24-hour cycle. They not only control when we fall asleep and wake up but also influence our appetite and metabolism.

To explore the circadian rhythms of Neanderthals and Denisovans, Dr. Capra and his colleagues looked at 246 genes that help to control the body clock. They compared the versions of the genes in the extinct hominins to the ones in modern humans.

The researchers found over 1,000 mutations that were unique only to living humans or to Neanderthals and Denisovans.

Their analysis revealed that many of these mutations probably had important effects on how the body clock operated.

The researchers predicted, for example, that some body-clock proteins that are abundant in our cells were much scarcer in the cells of Neanderthals and Denisovans.

Geography might explain why the ancient hominins were early risers. Early humans lived in Africa, fairly close to the Equator, where the duration of days and nights stays roughly the same over the course of the year. But Neanderthals and Denisovans moved into higher latitudes, where the day became longer in the summer and shorter in the winter. Over hundreds of thousands of years, their circadian clocks may have adapted to the new environment.