10 March 2022: ‘Us’ Part 6 – Kith and kin

Hobbits and their ancestors

One of the great palaeoanthropological bombshells of the last generation was the discovery of Homo floresiensis on the Indonesian island of Flores. For years scientists debated what ancestor this new and somewhat diminutive hominin – dubbed the ‘Hobbit’ by the media – had come from, or indeed if it should even be included in our genus.

Homo floresiensis reconstruction. Courtesy of Creative Commons. This image created by ATOR.

While now generally accepted as a member of our broader tribe, its origins are still fiercely argued, many insisting it’s nothing more than H. erectus that’s undergone insular dwarfism. But I think a 2017 paper written by Colin Groves, Debbie Argue, Michael Lee and William Jungers, convincingly demonstrates that H. floresiensis is not derived from H. erectus (or is a diseased example of H. sapiens), but rather from a much earlier hominim such as H. habilis or a sister species.[i]

A second paper, published in 2020[ii], backs up this hypothesis, and concludes with this statement:

‘ … something which on account of our inadequate current taxonomic framework we have to call “early Homo” differentiated in Africa, possibly as early as 2.8 (mya) … Subsequently, one or more members of this group reached the Mediterranean fringe and spread Out of Africa at 2.5 Ma. After successfully expanding over Asia, at least one of those hominins … gave rise to new species that reached the Caucasus by around 1.8 (mya), and thence Europe by ca. 0.9 (mya) … (the) eastward expansion (or occupation) in Asia of small-bodied and archaically-proportioned hominins continued, possibly in multiple waves; and, by ca. 0.8 (mya), representatives of this group had penetrated as far as insular southeast Asia, where H. floresiensis ultimately emerged … ’

Indeed, some scientists considered this possibility as early as 2005. A report about the brain of H. floresiensis published in Science in that year[iii] concludes with these lines: ‘Although it is possible that H. floresiensis represented an endemic island dwarf that, over time, became subject to unusual allometric constraints, an alternative hypothesis is that H. erectus and H. floresiensis may have shared a common ancestor that was an unknown small-bodied and small-brained hominin.’

Homo habilis. Courtesy of Creative Commons. Photographer unknown.

I think an increasing weight of evidence strongly suggests that the first major exodus of our genus from Africa was carried out by H. habilis or one or more of her sisters. Furthermore, I think it’s possible that these closely related species then gave rise to H. erectus, H. pekinensis, H. luzonensis[iv] and H. floresiensis in Eurasia, while those remaining in Africa gave rise to H. ergaster. This does not preclude the possibility, or perhaps probability, of any or all of these species crossbreeding if they ran across each other.

But what of H. sapiens, our own species? As with H. ergaster and H. erectus, the evidence here is convoluted, confusing and often contradictory.

Mongrel

For those, like Colin Groves, who think H. ergaster is a species in its own right, the line of descent works something like the following.

Homo heidelbergensis. Courtesy of Creative Commons. This image created by ATOR.

About 600,000 years ago, H. ergaster, either directly or through an intermediary species called H. rhodesiensis, gave rise to H. heidelbergensis. This species was our size physically, and his brain capacity was well inside the standards of Anatomically Modern Humans (AMH). Following the great tradition of hominin migration, something that seems as ingrained in our genus as bipedalism, some members of this new species moved to Europe[v]. About 400,000 years ago, they gave rise to H. neanderthalensis. In a case of ‘well, we’ll show you’, those who stayed behind in Africa gave rise to H. sapiens at least 300,000 years ago, and possibly as long as 350,000 years ago.[vi]

I can’t stress this enough. Homo sapiens are Africans. It is where our archaic ancestors and AMH first appear[vii]. (Let me also stress that this story, as complicated as it gets from now on, does not resurrect the Multiregional Model for our evolution, where H. erectus gave rise to H. sapiens across its whole range at the same time, from Africa to Asia. This is an old theory, now largely discredited by the extensive fossil and DNA evidence that our species first evolved in Africa.[viii])

What happened next has been slowly and painstakingly uncovered by palaeoanthropologists doing field work throughout Africa and Eurasia, and by the outstanding work performed at the Max Planck Institute’s Department of Evolutionary Genetics, headed up by Svante Pääbo, into hominin DNA.[ix]

What the DNA evidence strongly suggests is that H. sapiens successfully left Africa between 70,000 and 100,000 years ago. (Although this wasn’t the first migration into Eurasia by our species. It is usually held that previous attempts left no trace in the DNA of AMH outside of Africa, but see these earlier posts, here and here.)

Female Homo neanderthalensis. Courtesy of PLOS ONE.

Members of the most recent migration interbred with H. neanderthalensis, probably in what is now the Middle East, and later with the Denisovans, another possible descendant of H. heidelbergensis, deeper in Eurasia[x]. To this day, the average ex-African H. sapiens carries between 1%-2% of the Neanderthal genome; but it is not the same one or two percent: we overlap. Overall, we carry up to 40% of the Neanderthal genome in our own genes. But the story gets more complex still: the genome of people from Oceania, such as Papuan New Guineans and Australian Aborigines, can have between 5-6% Denisovan DNA[xi]; indeed, recent research suggests that Ayta Magbukon Negritos in the Philippines have Denisovan ancestry 30-40% higher than either of these two groups.

The Natural History Museum of London’s Professor Chris Stringer says, ‘It is now clear there was a lot more interbreeding between ancient species, including early Homo sapiens and others, and that there was a lot more movement of populations both in the distant past – and relatively recently.’[xii]

Homo sapiens (Oase 2) reconstructed from bones 37,000-42,000 years old discovered in the cave of Peştera cu Oase in Romania. Around 7.3% of his DNA is from H. neanderthalensis, from an ancestor 4-6 generations back. Courtesy of Creative Commons. Photo: Daniela Hitzemann.

Talking about recent research, in June last year Chinese scientists announced that a cranium first discovered in China almost a century ago, is a new species of Homo with a brain easily the equal of any AMH in size and carried inside a skull more massive than ours. Those making the announcement have named the new species H. longi (‘Dragon man’, and just as Denisovans are sometimes described as a sister species to Neanderthal, so H. longi is being claimed as a sister species to H. sapiens[xiii]).

As Lee Berger, from the University of Witwatersrand and the discoverer of Australopithecus sediba and H. naledi, has suggested, perhaps the different paths of human evolution are not best thought of as branches spreading from a single tree trunk, or even a messy, many-twigged bush, but rather a braided stream[xiv] with tributaries constantly running across each other before separating, rejoining and separating once more.

The Waimakariri River in New Zealand is braided along almost its entire length. A good metaphor for hominin interbreeding? Courtesy of Creative Commons. Photo: Greg O’Beirne.

We, Anatomically Modern Humans, are the result of all this evolution. We are nothing more than a mongrel species.

What a splendid, exhilarating thought.

Other posts in this series can be found here:

‘Us’ Part 1 – Out of Africa

‘Us’ Part 2 – Burdalone

‘Us’ Part 3 – The devil in the detail

‘Us’ Part 4 – Using your noggin

‘Us’ Part 5 – Feet and socks


[i] https://www.sciencedirect.com/science/article/abs/pii/S0047248417300866

And this from the Australian Museum: ‘Most scientists that accept H. floresiensis as a legitimate species now think its ancestor may have come from an early African dispersal by a primitive Homo species similar in appearance to H. habilis or the Dmanisi hominins. This means that it shared a common ancestor with Asian H. erectus but was not descended from it. Cladistic analysis supports the lack of a close relationship with H. erectus.

[ii] https://onlinelibrary.wiley.com/doi/abs/10.1002/evan.21863

[iii] Falk, Dean, et al. ‘The Brain of LB1, Homo floresiensis’. Science, 308, 242 (2005).

[iv] https://www.nature.com/articles/s41586-019-1067-9

[v] The first H. heidelbergensis fossils were found near Heidelberg in 1907.

[vi] Although this paper suggests the split between our two species might be found much further back … up to 800,000 kya or more!

[vii] Recent research from scientists at Australia’s Garvan Institute of Medical Research reveals that southern Africa is home to the oldest evidence for AMH: ‘… to contemporary populations that represent the earliest branch of human genetic phylogeny.’ The date they arrive at is 200,000 years ago.

As well, a report in the February issue of Science describes how thousands of genome sequences were collected from modern and ancient humans to create a family tree. In the words of the report’s first author, Anthony Wilder Wohns, ‘ … we definitely see overwhelming evidence of the Out-of-Africa event … ‘

[viii] See Stringer, C. & Andrews, P. The Complete World of Human Evolution. London, 2011. P 140 ff for a discussion of the two main theories for the evolution of Home sapiens: ‘Multiregional’ and ‘Out of Africa’.

[ix] And now, besides DNA, they are using protein analysis to identify ancient hominins, most recently the first Denisovan found outside of the Denisova Cave in Siberia … on the Tibetan Plateau of all places! See https://www.nature.com/articles/s41586-019-1139-x, 16 May 2019.

[x] Very recently, H. sapiens remains were discovered in the Grotte Mandrin rock shelter in the Rhône Valley in France that date back 54,000 years ago, pushing back our species arrival in Europe by at leat 10,000 years from previous estimates.

[xi] Please watch this fascinating talk Svante Pääbo gave at the University of California in 2018 after receiving the Nierenberg Award for Science in the Public Interest. It goes into all of this in much more detail. As Pääbo points out in the talk, the DNA evidence indicates humans ‘have always mixed’.

[xii] https://www.theguardian.com/science/2017/nov/19/human-evolution-dna-revolution-mapping-genome

[xiii] See here and here.

[xiv] See Berger talk about this towards the end of this Nova documentary, the Dawn of Humanity.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s