Testing the Out of Africa model in East Eurasian genomic origins

University of Tokyo researchers have investigated the origin and dispersal scenarios of Homo sapiens into East Eurasia. The team examined how migration routes, genetic contributions from archaic humans, and environmental adaptations helped shape modern populations and found an improbable flaw in one origin idea.

Origin and dispersal of Homo sapiens has been widely, though ever more narrowly, debated between two main competing models—the Multiregional Evolution model and the Out of Africa model.

The Out of Africa model suggests that Homo sapiens originated in Africa and dispersed globally and remains the dominant scientific consensus over the past 30 years, primarily due to advances in genomic research.

Multiregional Evolution models propose that modern humans evolved from archaic populations in multiple regions simultaneously. A major flaw in the Multiregional Evolution model is the improbability of identical mutations leading to brain expansion occurring independently in multiple populations worldwide.

While Multiregional Evolution was previously considered in Western academia, it is currently most associated with Chinese anthropologists and archaeologists, who support the idea that modern East Asians evolved directly from local archaic humans, such as Peking Man (Homo erectus pekinensis), rather than from African Homo sapiens. This view is influenced in part by early fossil discoveries in China as well as more nationalistic interpretations of human origins.

In the study, “Human dispersal into East Eurasia: ancient genome insights and the need for research on physiological adaptations,” published in the Journal of Physiological Anthropology, researchers applied genomic analysis and archaeological assessments to evaluate migration patterns and physiological adaptations.

Whole-genome sequencing of both modern and ancient human populations was used to determine dispersal routes into East Eurasia. Mitochondrial DNA, nuclear DNA from autosomes and sex chromosomes, and paleogenomic data from Neanderthals and Denisovans were analyzed.

Researchers also examined physiological adaptations, including cold resistance, metabolic shifts, and light sensitivity, through genomic variants.

Genomic evidence from large-scale projects, including the HapMap Project and 1000 Genomes Project, confirmed that modern non-African populations share a common ancestor who left Africa approximately 60,000 years ago.

The study also confirmed that African populations possess the highest genetic variation, supporting an African origin for all modern humans.

The study investigated two possible migration paths into East Eurasia. A northern route passing north of the Himalayas, and a southern route through the Indian subcontinent and Southeast Asia before reaching East Asia.

Genetic studies, particularly from the Pan-Asian SNP Consortium, strongly support the southern route as the primary migration path for the ancestors of modern East Asians, including Han Chinese, Japanese (excluding Jomon ancestry), and many Southeast Asian populations.

Genome analysis of the Jomon people, an ancient population of Japan, indicated that modern East Asians do not have significant northern route genetic contributions, whereas Native Americans and Northeast Asians do. The Northeast grouping includes Siberians, Mongolic populations, and some Indigenous groups in China, Korea, and Japan.

Introgression from Denisovans and Neanderthals played a significant role in physiological adaptations, including cold resistance, metabolism, and immune function. TBX15/WARS2 and UCP1 influenced thermogenesis, while Neanderthal DNA contributed to immune defenses, pigmentation, and circadian rhythm regulation.

Cold adaptation from Denisovans in the TBX15/WARS2 gene is linked to thermogenesis and body fat distribution and can be found in high frequencies among East Asians and the Inuit. East Asians, whose ancestors endured Siberian winters, exhibit higher basal metabolic rates, potentially reducing their obesity risk compared to other populations.

Denisovans also contributed the EPAS1 gene, which facilitates the Tibetan people’s high-altitude adaptation.

Neanderthal-introgressed genes in the OAS gene cluster strengthened antiviral immune responses. Pigmentation genes inherited from Neanderthals helped adjust to lower UV exposure in northern latitudes.

Ancient genetic adaptations that once conferred survival advantages may now contribute to modern health issues, including obesity and type 2 diabetes risk. The thrifty gene hypothesis suggests that cold-adaptive genes promoting fat storage became disadvantageous in modern environments with abundant food availability. A gene inherited from Neanderthals, SLC16A11, has been associated with higher diabetes risk, particularly in Mexican and Latin American populations.

Evidence confirms that modern East Asians descended primarily from southern route migrants, while Native Americans and Northeast Asians exhibit a mix of northern and southern ancestry, all with arrows that point to a shared African starting point.

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