Artists impression of a group of australopith

The Origin of ‘Us’: What We Know So Far About Where We Humans Come From

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Chimpanzee (top left), (CC BY-SA 3.0); Orangutan (top right) (CC BY-SA 3.0); Gorilla (bottom left) (CC BY-SA 3.0); Bonobo (bottom right); (CC BY 3.0)

Chimpanzee (top left), ( CC BY-SA 3.0 ); Orangutan (top right) ( CC BY-SA 3.0 ); Gorilla (bottom left) ( CC BY-SA 3.0 ); Bonobo (bottom right); ( CC BY 3.0 )

More and better data are steadily being accumulated, and in 2013 a review of ape DNA based on the genomes of 79 great apes was published.

These new ape genome sequences support the results of earlier analyses of both nuclear and mitochondrial DNA that suggested modern humans and chimpanzees are more closely related to each other than either is to the gorilla.

When DNA differences among modern humans and the great apes are calibrated using the best palaeontological evidence for the split between the apes and the old world monkeys, those differences predict that the hypothetical common ancestor of modern humans, chimpanzees and bonobos lived about 8 million years ago.

The Rise of the Hominins

Most researchers now recognize the modern human as hominins.

Still, the question “where do we come from” can from a scientific perspective be difficult for someone outside of the discipline to come to grips with. In part this is because the fossil record for human evolution seems to grow exponentially, with the author of each new discovery often claiming that the textbooks need to be rewritten.

The interdisciplinary nature of palaeoanthropology also means that new evidence that helps us make sense of our ancestry does not always come in the form of new fossils.

It comes from advances in a range of disciplines that include archaeology, comparative anatomy, earth sciences, evolutionary biology, genomics and primatology.

A further complicating factor is that the human fossil record does not just consist of the fossil evidence of our direct ancestors.

Many of the fossils belong to lineages that do not make it to the surface of the Tree of Life . They belong to extinct close relatives, and the task of sorting close relatives from ancestors is one with which we are only just now beginning to grapple.

There is a lineage that leads to today’s Homo sapiens , but there are also a host of side experiments that are equally important to understand. They represent some of the most interesting chapters in human evolution.

Origins of the genus Homo

Understanding the origins of our own genus Homo means establishing what fossils we recognize as being the first early humans.

Sometime before 4 million years ago we see the first evidence of the genus Australopithecus. These fossils sample the kind of creature that was most likely the ancestor to the genus Homo.

Australopithecus afarensis - forensic facial reconstruction.

Australopithecus afarensis - forensic facial reconstruction. ( CC BY-SA 4.0 )

Around 2.5 million years ago we see the first fossil evidence of species in Africa that many argue belong to our own lineage. One of these, Homo habilis , almost certainly made stone tools, had a slightly larger brain than Australopithecus, stood upright and regularly walked on two legs.

Some recognize a second species, Homo rudolfensis , about which we know even less.

These possible human ancestors lived alongside close relatives that were almost certainly not our ancestors. These species are called Paranthropus or robust australopiths – they had small brains, big jaw bones, large flat faces, and huge chewing teeth.

They lasted for at least a million years, so whatever they were eating (which is still a mystery) they were successful in the sense that they lasted as long in the fossil record as the average mammal.

But some researchers think that Homo habilis and Homo rudolfensis are not different enough from the australopiths that preceded them to justify being included in the genus Homo.

They claim that the size and shape of their body and the size of their teeth and jaws was little different from that of the australopiths. This means that their locomotion and diet had not shifted far enough in the direction of pre-modern Homo species such as Homo erectus to justify inclusion in Homo.

Artists impression of a group of australopiths.

Artists impression of a group of australopiths. (Public Domain )

Tool Making is not Enough

Also, because it is becoming evident that australopiths may have been making tools earlier than Homo habilis it means that tool-making can no longer be seen as the sole prerogative of Homo.

There is a developing consensus that the relaxation of the criteria more than 50 years ago that saw the inclusion of Homo habilis into the genus Homo needs to be reconsidered .

Species that emerge slightly later from Africa, such as Homo ergaster , fit much more clearly within what we understand by the genus Homo. That species probably left Africa around 2 million years ago and migrated ultimately as far east as China and Indonesia where it evolved, eventually, into Homo erectus .

A number of further migrations out of Africa probably occurred after the initial Homo ergaster migration, one of which, Homo heidelbergensis , is considered by many palaeoanthropologists to be the ancestor of both Neanderthals ( Homo neanderthalensis ) and modern humans ( Homo sapiens ).

As far as we know, Neanderthals evolved outside of Africa, perhaps in response to the ice ages of Europe. Our ancestors remained in Africa where perhaps as early as 300,000 years ago, as revealed from recent redating of the Moroccan site of Jebel Irhoud, were well along in the process of evolving into modern humans .

Representation of a group of Neanderthals.

Representation of a group of Neanderthals. ( Public Domain )

So the Origins of ‘Us’

Once we get to the origins of our own species Homo sapiens we have the added advantage that we are able to now use next generation sequencing methods to recover ancient DNA (aDNA).

As geneticists recover ancient genomes from different extinct hominin species, they are generating insights that are not possible from comparing the anatomy of the fossils alone.

There is now fossil evidence from teeth to suggest that Homo sapiens may have been in China by 120,000 years ago and in South East Asia by 67,000 years .

The discovery of some distinctive modern human DNA within the DNA recovered from a Neanderthal fossil suggests that modest interbreeding was occurring between Neanderthals and modern humans in Central Asia by 100,000 years ago.

Modern humans have not shared the planet with another hominin species for several tens of thousands of years. But before that, in the past 300,000 years or so, there is fossil and DNA evidence of several hominin species, including the recently reported archaic hominin Homo naledi

Reconstruction of homo sapiens, MUSE Science Museum of Trento.

Reconstruction of homo sapiens, MUSE Science Museum of Trento. ( CC BY-SA 3.0 )

First and foremost there was Homo neanderthalensis , whose range overlapped with modern humans in the Near East. Neanderthals most likely became extinct as a result of direct competition with the more technologically sophisticated Homo sapiens .

The evidence from DNA shows that there was interbreeding between our species and pre-modern humans, including the Neanderthals and the other enigmatic hominin referred to as the Denisovans.

We do not yet know how and when Homo erectus became extinct. It would appear that another unexpected side experiment in hominin evolution, known from the island of Flores and called Homo floresiensis most likely became extinct sometime after 60,000 years ago.

Indeed this hominin may represent something far more significant than simply an interesting side experiment, with many leading palaeoanthropologists arguing that the Hobbit may represent a pre-ergaster migration out of Africa .

What Next?

Even though thousands of hominin fossils have now been recovered and described there is still much work to be done.

Was there a hominin that successfully migrated out of Africa prior to Homo ergaster ? Did most of human evolution occur in Africa? Did some important transitions occur outside of Africa?

When did Homo erectus become extinct, and was there genetic exchange between erectus, sapiens and perhaps other hominin species?

As is often the case in science, with the recovery of additional data, in this case fossils and DNA extracted from fossils, we generate more questions than answers.

But ultimately all of this new evidence will result in a far more sophisticated appreciation of not only our evolution, but also the evolution of our extinct fossil cousins.

Top image: Artists impression of a group of australopiths. (Public Domain )

This article was originally published under the title ‘ The origin of ‘us’: what we know so far about where we humans come from ’ by Bernard Wood and Michael Westaway on The Conversation , and has been republished under a Creative Commons License.

Comments

You did the exact same thing Linneaus did, you presented a picture comparing a chimpanzee and human sitting to make a taxonomical comparison. Does that mean because we sit that is a proper comparison?

How did Linneaus come up with the taxonomical chart? He said humans are apes because we have two eyes in the front, two ears on the side, two arms and two legs. Does that mean we are apes?

May I remind that even today some people still claim Neanderthals are merely cousins, yet so many are DESCENDED from Neanderthals. See, how it works is this, if you are part something that means your ANCESTORS were that and you are DESCENDANTS. That threw the wrench into the whole works as Neanderthals were not African and no indigenous Africans had Neanderthal ancestry.

While it is very easy to fall back onto Linneaus for explanations (which is what Darwin did), you fail to see the bigger picture. And using genetics only makes it worse for the case of evolution by random mutations. There is not one single yDNA or mtDNA haplotype that is the same for any primate and human group. In other words, since the yDNA and mtDNA is passed from parent to child unchanged, and there is no primate that shares those with any human, it is even more suspect for the claim.

Now, since the claim is that all humans came out of Africa and yet Africans had no Neanderthal or Denisovan, yet "Anatomically Modern Humans" umbrella all human groups, and "Anatomically Modern Humans" were supposedly from Africa, then perhaps the term should not be used. You can't include Europeans with high percentages of Neanderthal as AMH when Africans who have no Neanderthal ancestry are also called AMH.

Which should it be now?

And it is amazing that people are constantly invoking Darwin to make their claims after Darwin has been debunked AND in his own writings was a racist attempting to place Africans as the closest to monkeys. Actually read his books and you will see.

Remember, when talking about "descent with modification", that first word descent means DESCENDANT, which means that one has an ANCESTOR. My ancestors were Neanderthals. Genetics testing proves it. And if you are of European descent, then most likely your ancestors were also Neanderthal.

There is not one single shared mtDNA between me and any ape. Why not? If we have the same maternal ancestress, then we should share.

I'm not doubting evolution, but I wonder why some of the apes are still apes while others of us have evolved.

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