That? That’s how it is. Neanderthals made us early risers (at least a little). The genetic material that we inherit from them promotes this propensity. This is revealed by a study in ‘Genome Biology and Evolution’.
All anatomically modern humans originated in Africa about 300,000 years ago. There environmental factors shaped many of its biological characteristics. About seventy thousand years ago, the ancestors of modern humans from Eurasia began to migrate to that continent. There they encountered new environments, higher latitudes with greater seasonal variation in daylight and temperature.
Inherited traits
Other hominids, such as Neanderthals and Denisovans, had lived in Eurasia for more than 400,000 years. These archaic hominids diverged from modern humans about 700,000 years ago. As a consequence, our ancestors and archaic hominids evolved in different environmental conditions. This resulted in the accumulation of genetic variations and phenotypes specific to each lineage. When humans arrived in Eurasia, they interbred with the continent’s archaic hominids. Humans acquired genetic variants already adapted to these new environments.
For example, archaic genetic variants for higher altitude hemoglobin levels appear in Tibetans. Also immune resistance to new pathogens, skin pigmentation levels and fat composition. Changes in the pattern and level of light exposure have biological and behavioral consequences. Eurasian environments had more variable daylight than the landscape in which modern humans evolved before leaving Africa.
In humans, the increased tendency to wake up early is associated with a shorter period of the circadian clock. This is likely to be beneficial at high latitudes. Allows faster alignment of sleep/wake with external temporal cues.
Getting up early
The tendency to wake up early may indicate selection toward a shorter circadian period in populations living at high latitudes. Being a morning person was evolutionarily beneficial for our ancestors who lived in higher latitudes in Europe. Therefore, it would have been a Neanderthal genetic characteristic worth preserving.
Neanderthals made us early risers, because traces of their circadian cycles remain in some of us. Despite hundreds of thousands of years of difference, they are still there, in our behavior, like a persistent ghost.
