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Modern humans, or Homo sapiens, are the only species of human living on the planet. But this wasn’t always the case – it’s been a long evolutionary journey to get to where we are now, from our early hominid ancestors the Australopithecines to the big-brained, flat-faced people we are now. This post will look at the different hypotheses to explain how we got here, as well as the evidence used to examine our species.

The earliest ancestors of humans are believed to be from the Austrilopithecus genus, which first appeared during the Pliocene, as early as 4 million years ago (Pickrell, 2006). These guys were very ape-like, with long strong arms and a small brain, who could also move bipedally (on two legs). From them, Homo habilis developed with a larger brain size and the capability to manufacture tools, followed by Homo erectus, which was around until 250,000 years ago, and whose long legs and shorter arms made them better adapted to walking longer distances than climbing trees (Natural History Museum). The evolutionary tree is not a straight line from one species to the next, as there are several branches of species which evolved in different places (see figure below) – for example, European Neanderthals or Homo neanderthalensis are believed to have evolved from the early hominids who left Africa over 1.75 million years ago, when in Asia instead Homo erectus was the dominant species before us (Johanson, 2001).

A timeline for human evolution, from 4 million years ago (bottom of the figure) to present. The figure shows that different species evolved in different areas, and that our evolutionary history is complex and still debated today.  Unlike Pokémon, we are not simply the linear evolutionary upgrades of each other, though that would be easier to understand. Source: https://earthhow.com/human-evolution-timeline/

A migration from Africa around 1.75 – 2 million years ago saw the spread of early homonids around the world (“homonid” being the term used to group all the modern and extinct great apes and human ancestors), which eventually resulted in the development of genetically distinct species such as the Neanderthals across Asia and Europe (Johanson, 2001; Blaxland & Dorey, 2020). But the much later migration is the topic of this post because it saw the first migration of our own species, Homo sapiens.

The evolution of Homo sapiens is believed to have occurred in Africa and the Middle East (Johanson, 2001), with the first anatomically and genetically modern individuals emerging around 200,000 years ago and migrating across Asia and Europe 65,000 years ago (Mellars, 2006). This raises two questions: how did early humans get out of Africa and around the rest the world? And why did it take them so long?

In their research on the subject, Mellars (2006) looked at a combination of DNA and archaeological findings to suggest that technological and behavioural changes could be the reason behind the expansion of the first Homo sapiens out of Africa. Such changes arose from the need to adapt to changing environmental conditions, like the rapid shifts between wet and dry periods across the continent between 80-70,000 years ago (Mellars, 2006). Findings of more advanced hunting and carving tools and dense accumulations of plant remains suggests an expansion in the complexity of human behaviour (Mellars, 2006), and indicates a population which was managing their crops and exploiting their food to a much greater efficiency (Mellars, 2006). The movement of stone and shells may also indicate an increased level of cooperation between human groups (Mellars, 2006). This is important as it suggests widescale changes in the way that these early people lived, which could have given rise to a population expansion and subsequent movement out of Africa.

increased levels of technological efficiency and economic productivity in one small region of Africa could have allowed a rapid expansion of these populations to other regions and an associated competitive replacement.” – Mellars, 2006

Evidence suggests that the expansion of anatomically modern humans came from one small area to the East or South of Africa, before migration to southern Asia 60,000 years ago occurred (Mellars, 2006; Wood, 2017). This outlines the “Out of Africa” theory – Homo sapiens (modern humans) migrated from Africa and colonised the world from there, replacing the other species already there since the first migration (such as the Neanderthals, who had become genetically distinct from other populations by 130,000 years ago) (Johanson, 2001). In contrast, the “Multiregional” model suggests that all living humans derive from Homo erectus, a more primitive human species, which left Africa almost 2 million years ago. When populations became isolated across different parts of the world, they slowly evolved into different species through natural selection in regional populations (Johanson, 2001).

A summary of the differences between the two hypotheses. The out of Africa model suggests that our species evolved in Africa and then spread, when the multiregional hypothesis suggests that Homo sapiens evolved separately in different places.

Most current research supports the Out of Africa hypothesis. This is because DNA analysis points to a recent African ancestor of modern-day humans who was still in Africa 60,000 years ago (thus suggesting that Homo sapiens evolved there, and not in another regional location), and one who used more advanced tools and technology than earlier species of homonids (Galway-Witham & Stringer, 2018; Mellars, 2006). So even though other species were around and living alongside Homo sapiens, for example alongside the Neanderthals for around 10,000 years, modern humans dominated – they competed with them, interbred with them (rarely), and then finally, killed them all off.

 “By 100,000 years ago, humans had dispersed and diversified into at least four species. Our own species, Homo sapiens, lived in Africa and the Middle East, Homo neanderthalensis lived in Europe, and Homo floresiensis in southern Asia.” – Blaxland & Dorey (2020)

Neanderthal Man | A MKU3A visit to Kensington and the ...
A reconstruction of a Neanderthal male.

Modern day humans are characterised by their vertical foreheads, reduced brow bones (compared to the frowny fellas, the Neanderthals) and a less robustly built skeleton (Johanson, 2001). With the evolution of anatomy came the evolution of mind and behaviour (Kisse & Fuentes, 2016), which led to the earliest members of our species competing with and killing all the other hominid species. What a positive way to start a global society! This post is difficult to summarise, given that we are still going and have yet to be replaced by anything else, so let me know your thoughts in the comments – what’s next for the human race?

“What makes us human, more than the fact that we are bipedal, eat cooked foods, or can think symbolically, is our shared evolutionary history, during which time our ancestors expanded the human niche in remarkable ways.” – Kissel & Fuentes (2016)

References

Blaxland, B. & Dorey, F. (2020) The first migrations out of Africa. [online] Available at: https://australian.museum/learn/science/human-evolution/the-first-migrations-out-of-africa/ (Accessed: 08/07/2020)

Galway-Witham, J. & Stringer, C. (2018) How did Homo sapiens evolve?. Science360(6395), pp.1296-1298

Johanson, D. (2001) Origins of Modern Humans: Multiregional or Out of Africa?. Action Bioscience.

Kissel, M. & Fuentes, A. (2016) From hominid to human the role of human wisdom and distinctiveness in the evolution of modern humans. Philosophy, Theology and the Sciences3(2), pp.217-244

Mellars, P. (2006) Why did modern human populations disperse from Africa ca. 60,000 years ago? A new model. Proceedings of the National Academy of Sciences103(25), pp.9381-9386

Natural History Museum (n.d.) Homo erectus, our ancient ancestor. [online] Available at: https://www.nhm.ac.uk/discover/homo-erectus-our-ancient-ancestor.html (Accessed: 08/07/2020)

Pickrell (2006) Timeline: Human Evolution. [online] Available at: https://www.newscientist.com/article/dn9989-timeline-human-evolution/ (Accessed: 08/07/2020)

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Published by avleveri

Hi! I'm Anna, an environmental science graduate from the UK. My main interests (if you can't already tell from my blog posts) are sustainability, consumption, conservation, nutrition, fitness and food! Lots of food.

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