Through time, there have been over a dozen different species of humans. They all had a large cranial cavity & thus large brains, opposable thumbs, upright posture dexterity and tool usage. They all looked somewhat similar, reminiscent of modern hominins (humans, chimpanzees and bonobos) yet they still had distinct features. The first one is thought to have lived about 2.8 million years ago and off that first species, many other humans evolved, with as many as 9 species walking the Earth at the same time 300 thousand years ago. One of those species was us: Homo sapiens. During our early years, we shared our planet with 8 other human species. 300,000 years later, and we’re the only ones left. How did we get here?
It begins with a divergence. The first species belonging to the genus “Homo” (human) appeared 2.8 mya (million years ago) and evolved from “Australopithecus”, an early hominin. The first, single species of human is debated, with multiple different humans coexisting at the same time. The general consensus is that H. rudolfensis and H. habilis are the first clear species of humans. Even this is not fully agreed on, with certain scientists believing H. rudolfensis to be a subspecies of H. habilis. They share similar characteristics such as a brain size of around 600-800 cm^3. H. Rudolfensis is thought to be larger than H. habilis, with the presumed female specimen of Habilis being estimated at 100-120 cm tall while Rudolfensis is estimated at 150cm for females and 160cm for males.
Following Habilis and Rudolfensis, the next species of human is Homo erectus (upright human), first appearing 2-1.8 mya. H. erectus is divided into an “African (H. ergaster)” and an “Asian” subspecies with small differences. They’re considered to be the first species with similar body proportions to modern humans. This suggests an ability to traverse long distances and a higher adaptation to living on-ground. They’re also believed to be the first humans to have used stone tools such as axes. They’re closer to modern humans in their face shape and possible lack of body hair as well. Both sexes of the species is thought to be 145-185 cm tall, weighing 40-68 kg with an average brain size of 950 cm^3.
From H. erectus, Homo heidelbergensis evolved, either as a subspecies to H. erectus or a unique species, with the latter gaining more recognition in recent years. First emerging 0.7 mya, they’re similar to H. erectus in physical build, but differ from H. erectus in brain size. A specimen of H. heidelbergensis could have a brain size of 1200 cm^3, comparable to modern humans. They’re believed to be the first species of human to build shelters and were likely able to control fire.
After H. heidelbergensis, the next major human species to evolve was Homo neanderthalensis, commonly known as “Neanderthals”. Neanderthals emerged 0.4 mya, were likely directly evolved from H. heidelbergensis and are believed to be the closest extinct relatives of modern humans. Males averaged 164 cm and 65 kg while females averaged 155 cm and 54 kg. Their brain size was 1300 cm^3 on average, sometimes even exceeding it. They lived in colder environments such as Europe, and thus had large noses & shorter, robust bodies, supported by denser bones. They used tools, built shelters, used fire, wore clothing and had rituals.
After the evolution of Neanderthals, another species diverged from H. heidelbergensis: Homo sapiens, us. First appearing 0.3 mya, H. sapiens have lighter skeletons, smaller jaws & teeth and large brains compared to the earlier human species. They also sported a thinner skull, an almost vertical forehead and a chin. Their brains were usually 1300 cm^3. They’re thought to be the most intelligent species of humans.
Despite our lighter bone structure and thinner skulls, we’ve manage to be the fittest, the ones who’ve survived. What gave us an edge?
There are multiple hypotheses as to why we happened to be the humans that lived, that differ from each other quite a bit. Certain scientist suggested that we crossbred with other human species such as Neanderthals and assimilated their DNA. The recent Neanderthal genome project has provided some support for this hypothesis, with evidence suggesting that most living humans have Neanderthal DNA mixed into their genome.
Another possible explanation is that we had better coordination and social structures compared to other human species. There have been findings that a H. sapiens brain has a much better developed ability of language and speech compared to H. erectus. This might have allowed us to communicate more efficiently, increasing overall survival rates.
There are many more predictions as to what might have happened, from weaker immune systems to infant mortality rates, but for now, the answer lies buried beneath the ground, not yet reached by us, the ones remaining.
