Banner by Meghan Carlton

Wild Origins: Are We as Human as We Think?

by Nicholas Rosa

When we think of human history, we usually only go as far back as the birth of civilization as we know it. Very rarely do we tend to travel beyond 10,000 BCE. To fully understand our genetics and their phenotypic consequences, however, we must turn the clocks back hundreds of thousands of years to a time where other humanoid species roamed the earth -- a time where humans had yet to leave Africa, and other humanoid species, such as the Neanderthals and the Denisovans, roamed Eurasia. Many traits that have shaped humanity and helped us survive along the way were a result of these evolutionary counterparts.

The Neanderthals were generally found in Western Eurasia, while the Denisovans were generally found in the East. Despite the geographical boundaries all populations likely faced, humanity found a way to interbreed with these species. A recent study conducted by Villanea and Schraiber concluded that two to six percent of the human genome contains Neanderthal and Denisovan DNA. While these percentage may seem inconsequential, it is anything but small in a genetic context. To put the numbers in perspective, a famous 2005 study by Stefan Lovgren discovered that 96 percent of our DNA is identical to those of chimpanzees. That four percent holds vital instructions that make us the complex, civilization building animals we are today. Similarly, the two to six percent of the human genome that contains Neanderthal and Denisovan DNA has given us many traits of which we still exhibit now.

This human-Neanderthal-Denisovan gene flow was not exclusively an African event. In fact, it seems that the further east we go, the more DNA comes from these hominids. A study led by Benjamin Vernot revealed that descendants of early East-Asian populations have about 12 to 20 percent more Neanderthal DNA in their genome than other groups. It is also important to keep in mind that this was hundreds of thousands of years ago, when human populations were barely a fraction of what they are now. To keep things into perspective, historians speculate that the human population in 10,000 BC was between one and 10 million people. This was 90,000 years before that. That being said, humans were not frequently in sexual relationships with other hominids. In fact, it was exceptionally rare. However, over thousands of years, that very small population grew into the billions we know today, carrying genes from random flings in the middle of nowhere, tens of thousands of years before the wooly mammoth died out.

Research conducted by Martin Kuhlwilm and his team created an inference-based model regarding the symbiotic flow of genes between humans and other ancient hominids. Their study suggested a 3.3 to 5.8 percent gene flow from humans to Neanderthals, and a 1.0 to 7.1 percent gene flow from Neanderthals to humans. Despite these projections, research conducted by Mateja Hajdinjak and her team produced no evidence of gene flow from humans to Neanderthals. The study, however, does acknowledge the small sample size of Neanderthal genes. Evolutionary theories for why Neanderthal/Denisovan-human interbreeding occurred vary, but the most widely accepted is that Neanderthals and Denisovans had abnormally accentuated masculine features, something human women could have found attractive. Perhaps, this evolutionary factor can at least partially explain why no substantial evidence of gene flow from humans to Neanderthals has been observed. This theory implies that Neanderthal-human interbreeding was primarily an activity shared by male Neanderthals and human females, of which recent, albeit flawed, data has supported.

Strangely enough, without this form of interbreeding, we would not have many aspects of our humanity that have paved way for our current timeline. In fact, this interbreeding could be considered vital to human expansion into the upper-northern hemisphere. Contemporary research headed by biologist Carles Lalueza-Fox has discovered the prevalence of the melanocortin 1 receptor (MC1R) in Neanderthals, a gene sequence allowing for the absorption of more vitamin D from the sun, something necessary in areas with minimal sun exposure. It has been speculated that the transference of this gene from Neanderthals to humans could have benefitted them in their odyssey northward. The benefits of Neanderthal to human gene flow regarding migration, however, do not end there.

Research conducted by Dannemann, Andrés, and Kelso has discovered genetic code shared by both Neanderthals and humans related to the immune system. This research suggests that this genetic drift could have had allowed humans to migrate further north already being resistant to diseases prevalent in the area. While Neanderthal/Denisovan DNA was a major factor for human migration, not all genes passed to humans were beneficial. In fact, we can thank the ancient hominids for genes associated with both depression and a predisposition for certain allergies.

While evolution can seem like a million-year-old process, or something that only happens fast for small animals, some of our most significant historical feats, and some of our most heated social topics of today, are a direct result of evolution – an evolution of which is exceptionally recent relative to Earth’s timeline. In a time of technological feats and complex cities, one need only look inward to remain connected to past. After all, it is the many interactions between us humans and those hominids of the past that have shaped us into masters of this futuristic timeline in the first place.