How Primitive are We?

Are we really a unique, highly evolved “human” species, far from primitive Neanderthals, or are we more alike than previously thought? As much as 2.6% of modern human DNA was contributed by Neanderthals, our closest extinct relative. Utilizing modern genomic sequencing techniques allows us to trace human evolution and pinpoint when the “primitive cavemen” turned into “modern” humans.

Around 7 million years ago, the first hominids (a group including humans and their extinct ancestors or relatives) appeared in Africa, having diverged from ancestral primates. Ardipithecus, a group of early “proto-human” species that lived around 5 million years ago, reflected characteristics of both primates and humans, combining tree-climbing with elements of upright walking.

The genus Australopithecus, (of which the famous “Lucy” specimen belongs), appeared on African savannahs between 4 and 2.5 million years ago. These species pioneered bipedalism, allowing for the development of more advanced brains and behaviors. After the extinction of the Ardipithecus and Australopithecus groups, the genus Homo appeared in Africa. Large brains, fully bipedal movement, stone tool-making, and complex social groups allowed this genus to thrive and evolve into increasingly human-like species. Homo erectus, the first hunter-gatherer, migrated into East and West Asia between 1.8 million and 143,000 years ago. Homo heidelbergensis hunted large prey with spears, and built sturdy shelters. This was also the first species that distinctly utilized fire for survival in cold environments.

Three distinct species evolved from Homo heidelbergensis: Homo neanderthalensis, Homo sapiens, and a third mysterious group known as the “Denisovans”. Homo neanderthalensis and the Denisovans moved throughout Eurasia, while Homo sapiens remained in Africa. Homo neanderthalensis emerged in Europe and moved through Asia between 400,000 and 40,000 years ago, and was highly social and incredibly proficient in hunting large prey. Short, sturdy bodies and thick bones helped with retaining heat in cold regions, and allowed for powerful movement. They mastered the use of weapons and tools, made clothing, shelters, and ornamental objects, and practiced complex burials. Homo sapiens appeared in Africa 200,000 years ago, emerging at roughly the same time that Homo erectus and Homo heidelbergensis disappeared. Agile, smarter, dexterous, socially sophisticated, and well adapted for running, Homo sapiens quickly flourished as other species slowly disappeared. Around 70,000 years ago, groups of Homo sapiens moved from Africa into Europe and Asia (and eventually spread to Australia and the Americas). The overlap between Homo neanderthalensis and Homo sapiens often led to intense competition, interbreeding and possible warfare, and contributed to the decline and eventual extinction of Homo neanderthalensis.

Neanderthal DNA is extracted from ancient bone fragments often found in burial sites located in caves and mountain regions throughout Eurasia. Of the discovered fragments, genetic information is scarce, due to protein degradation over time. Because of this, only two separate Neanderthal individuals have been found with completely intact genomes. However, the DNA that has been found reflects fascinating interactions between humans, Neanderthals, and Denisovans. DNA sequenced from Neanderthal individuals found in Siberia, Croatia, and Spain have suggested multiple waves of interspecies breeding. Researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany proposed the following theory based on genetic evidence; Homo sapiens emerged in Africa 200,000 years ago, with some groups moving into Eurasia. One expanding group mated with Homo Neanderthalensis from Middle Eastern regions around 125,000 years ago. Although this specific lineage went extinct, their mixed DNA survived in other Neanderthals who traveled across Eurasia, eventually settling in Siberia. During this time, more Homo sapiens moved from Africa 60,000 to 50,000 years ago, and interbred again with these dispersed Neanderthal groups. Humans traveling East also briefly mixed with Denisovans in Asia. In short, modern humans interbred three times with non-human relatives, contributing non-human DNA to the modern human genome.

DNA evidence indicates that during the tenuous time Homo neanderthalensis and Homo sapiens coexisted throughout Europe and Asia, interbreeding occurred between the species. While outright warfare between the two groups could explain the extinction of Homo neanderthalensis, interbreeding suggests that dwindling populations became absorbed into Homo sapiens. Modern DNA sequencing techniques have revealed that 1.8% to 2.6% of modern human DNA in individuals of Eurasian descent comes from Neanderthals. People of African descent carry significantly less Neanderthal DNA, since African populations and Neanderthals occupied geographically separate regions, making contact unlikely.

Best adapted for cold weather climates, Neanderthals may have contributed genes that significantly improved early humans’ chances of survival. Neanderthal genetic variants that promote the buildup of LDL cholesterol (the “bad” cholesterol, which can lead to heart attacks) may have helped fat accumulation that insulates human bodies in cold, harsh climates they encountered during expansion from Africa. Another vital contribution to the human genome was immune resistance to new pathogens encountered during movement into Europe and Asia. By interbreeding, genetic resistance that Neanderthals accumulated over hundreds of years could be transferred into human populations. Not surprisingly, the majority of Neanderthal-based genes are found in regions of DNA that code for immune response to pathogens. Increased blood clotting may also stem from Homo neanderthalensis, which could have helped with recovery from injuries while hunting. Lighter skin (resulting from reduced concentration of the pigment melanin) allows for increased absorption of sunlight and higher rates of vitamin D synthesis, a useful trait in regions far from the equator where periods of daylight are shorter and less intense. Neanderthal DNA sequences contain mutations in melanin production similar to humans, suggesting that as humans developed unique mutations, Neanderthal influences would have strengthened their prevalence in interbreeding populations.

Although we are genetically different from Homo neanderthalensis, interaction between our species may have resulted in better adapted offspring with beneficial variations in immune function, skin pigmentation, and LDL cholesterol accumulation. By tracing our origins through interactions with other human-like species, we can better understand what makes us “human”, and how we are essentially “cavemen” in digital times.

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