Published in the journal Genome Biology and Evolution, the research delves into the origins of modern humans and their interactions with archaic hominins like Neanderthals and Denisovans. While all anatomically modern humans trace their roots back to Africa approximately 300,000 years ago, around 70,000 years ago, the ancestors of modern Eurasian humans embarked on a migration that introduced them to novel environments in Eurasia, marked by greater seasonal variations in daylight and temperature.
In contrast, Neanderthals and Denisovans had already inhabited Eurasia for over 400,000 years, diverging from modern humans around 700,000 years ago. As a result, our ancestors and archaic hominins evolved under distinct environmental conditions, leading to the accumulation of lineage-specific genetic variations and phenotypes. The interbreeding that occurred when modern humans reached Eurasia created the potential for the acquisition of genetic variants adapted to these new environments from the archaic hominins.
Previous studies have shown that while much of the archaic hominin ancestry in modern humans was not beneficial and was eventually eliminated by natural selection, some remaining archaic hominin variants in human populations exhibit signs of adaptation. These adaptations include associations with traits such as hemoglobin levels in Tibetans at higher altitudes, immune resistance to pathogens, variations in skin pigmentation, and fat composition.
The research sheds light on the evolutionary consequences of changes in light exposure patterns, which can impact both biology and behavior. While the evolution of circadian adaptation has been extensively studied in insects, plants, and fishes, it remains a relatively underexplored area in the context of human evolution.
The environments where Neanderthals and Denisovans resided in Eurasia featured higher latitudes with more variable daylight times compared to the landscapes where modern humans evolved before migrating out of Africa. In light of this, researchers investigated whether there was genetic evidence indicating differences in the circadian clocks of Neanderthals and modern humans.
By identifying a set of 246 circadian genes through a combination of literature review and expert knowledge, the researchers discovered hundreds of genetic variants specific to each lineage that had the potential to influence circadian clock-related genes. Utilizing artificial intelligence methods, they pinpointed 28 circadian genes containing variants capable of altering splicing in archaic humans and 16 circadian genes likely regulated differently between present-day humans and archaic hominins.
These findings suggested functional disparities in the circadian clocks of archaic hominins and modern humans. Given that the ancestors of Eurasian modern humans and Neanderthals interbred, it was plausible that some humans could have inherited circadian variants from Neanderthals.
To test this hypothesis, the researchers investigated whether introgressed genetic variants—variants transferred from Neanderthals to modern humans—were associated with preferences for wakefulness and sleep in a large cohort comprising several hundred thousand individuals from the UK Biobank.
The study revealed numerous introgressed variants with discernible effects on sleep preference, with a notable trend: these variants consistently heightened “morningness,” indicating a proclivity for early waking. This directional effect aligns with observed adaptations to high latitudes in various animal species.
The heightened morningness in humans correlates with a condensed circadian clock period, a trait likely advantageous at higher latitudes. This condensed period facilitates a quicker alignment of sleep-wake cycles with external environmental cues, especially important in regions with extended summer light periods. In fruit flies, for instance, shortened circadian periods are necessary for synchronization with the prolonged daylight of high latitudes, resulting in latitudinal clines reflecting decreasing circadian periods with increasing latitude in natural fruit fly populations.
The prevalence of morningness in introgressed variants suggests a selection toward a shortened circadian period in populations residing at high latitudes. The evolutionary benefit of being inclined toward morning activities could have been advantageous for our ancestors living in higher latitudes in Europe, making it a Neanderthal genetic trait worth perpetuating.
The lead author of the study, John A. Capra, highlighted the significant findings achieved by integrating ancient DNA, extensive genetic studies in modern humans, and artificial intelligence. The research uncovered substantial genetic distinctions in the circadian systems of Neanderthals and modern humans. Through analysis of the remaining fragments of Neanderthal DNA within modern human genomes, a noteworthy pattern emerged: a considerable number of these fragments influenced the control of circadian genes in modern humans, consistently pushing individuals towards a heightened predisposition to be early risers or “morning people.”
This observed change aligns with the impact of living at higher latitudes on the circadian clocks of animals and is likely to facilitate a more rapid alignment of the circadian clock with shifting seasonal light patterns. The next stages of the research involve extending these analyses to more diverse modern human populations, exploring the effects of identified Neanderthal variants on the circadian clock in model systems, and applying similar analytical approaches to investigate other potentially adaptive traits.
Resources
- ONLINE NEWS Oxford University Press. (2023, December 14). Neanderthals may have been morning people, says new study. Phys.org. [Phys.org]
- JOURNAL Velazquez-Arcelay, K., Colbran, L. L., McArthur, E., Brand, C. M., Rinker, D. C., Siemann, J. K., McMahon, D. G., & Capra, J. A. (2023). Archaic introgression shaped human circadian traits. Genome Biology and Evolution, 15(12). [Genome Biology and Evolution]
Cite this page:
APA 7: TWs Editor. (2023, December 16). New Study Suggests Neanderthals Were Early Risers. PerEXP Teamworks. [News Link]
