Between 60 and 70 thousand years ago, the ancestors of modern humans were on the move, and their sexual behavior made it more likely for their modern descendants to be early risers, according to a new study.
Migrating into Europe, our ancient human ancestors came out of Africa and encountered Neanderthals and Denisovans – with whom we share 93 percent of our DNA.
New research suggests that the three groups interbred and passed on genes that helped the following generations adapt to the northern climate and sunlight.
Among these were gene variants known to be associated with ‘morningness,’ including ones specifically shown to regulate circadian rhythm, our wake-and-sleep cycles.
So if you tend to wake up early in the morning, this may be why.
When ancient humans migrated north into Europe out of Africa, they encountered (and mated with) the Neanderthal and Denisovan populations who already lived there. This intermingling passed on genes to many of their modern descendants, including genes associated with early rising
To find out ancient genes’ modern-day impact, a team of researchers at Vanderbilt University, the University of Pennsylvania, and the University of California San Francisco combed through genetic data from a catalog of hundreds of thousands of people in the United Kingdom.
Specifically, they performed a genome-wide association study (GWAS) to look for traits linked to early rising.
A GWAS looks at the gene variants that are statistically connected to people’s traits. In the past, GWAS have been responsible for identifying genes that increase people’s risk of developing conditions like kidney disease or insomnia.
They compared these associations to the genomes derived from three ancient hominins that scientists had previously published: a 120,000-year-old Neanderthal and a 72,000-year-old Denisovan found in the mountains of Mongolia, and a 52,000-year-old Neanderthal from modern-day Croatia.
Woven into the fabric of these ancient hominins’ DNA were 16 variants associated with greater levels of ‘morningness’ in modern humans.
And among these were ‘clock genes’ that specifically help regulate our circadian rhythm.
When moving farther north, rising earlier may have offered some benefit to ancient humans. Shorter circadian rhythms seem helpful for to places where the days are shorter
It’s long been suspected that this intermingling of DNA between modern human ancestors and hominins passed certain tendencies to their descendants.
These adaptations may have helped them adapt to moving into more northern latitudes, scientists suspect.
Compared to Africa, Europe and Asia had greater seasonal differences in weather and sunlight.
And the genes identified in the new study may have shifted people toward a shorter circadian period, helping them survive the relatively shorter days.
Shorter circadian period, research suggests, helps people adapt to changing conditions more quickly.
‘By analyzing the bits of Neanderthal DNA that remain in modern human genomes we discovered a striking trend: many of them have effects on the control of circadian genes in modern humans and these effects are predominantly in a consistent direction of increasing propensity to be a morning person,’ said senior author John Capra, associate professor of epidemiology and biostatistics at the University of California San Francisco, in a statement.
‘This change is consistent with the effects of living at higher latitudes on the circadian clocks of animals and likely enables more rapid alignment of the circadian clock with changing seasonal light patterns.’
The results appeared today in Genome Biology and Evolution.
Neanderthals and Denisovans have gone extinct, but traces of their genetic legacy live on in many modern humans alive today
Modern humans may have benefited from Neanderthal and Denisovan genetics, but unfortunately, this genetic Silk Road was not an even trade.
The Neanderthals got the short end of the stick, past research has indicated: Interbreeding with modern humans may have led to a blood disorder that ultimately triggered their extinction.
Some important limitations accompany the new research.
First of all, humans carry many thousands of genes, and behaviors are complex, involving far more than just one or two of them.
And even though a GWAS can reveal genes linked to early rising, something as complex as our morning behaviors is difficult to pin to just a handful of genes.
Second, circadian rhythm genes is not just about when people wake up.
While sleep-and-wake behaviors are a big part of circadian rhythm, there are other processes in our bodies, like digestion, that are dictated by circadian rhythm.
So the genes that affect circadian rhythm may not only affect morning behaviors.
