The first Asians were not Homo erectus

 
Although I have been following paleoanthropology through scientific magazines for decades, recent discoveries have overturned what I have previously learned about human dispersion out of Africa. So, before embarking on our “Neanderthal in America” thesis lets brush up on what is currently going on in the hominid field so that we can put things in perspective.

The late Twentieth Century Hominid scenario

What I knew was this: after a long chain of Australopithecines, the first member of genus Homo appeared.
It was the primitive forbearer of mankind,Homo habilis (Latin for skilful man) who lived in Eastern Africa about 2.3 M years ago. They had a small brain (600 cm³) and were quite small (1.3 m - roughly 4.25 ft.) yet they developed a simple stone tool technology known as “Oldowan”. They disappeared about 1.4 M years ago.

Oldowan stone tools were of the “core and flake” variety, in which a stone core was hit with a hammer stone chipping it to produced flakes and leaving a “chopper core” both flakes and core were used to cut, bash and scrape.
It is the earliest (oldest) stone tool industry dating back to about 2.6 M years ago. It was replaced 1.7 M years ago by the more advanced Achulean technology.

If Oldowan tools are found, you can be certain that they predate the discovery of Acheulean tools and therefore belong to a group that predates the inventors of these tools.

About 1.8 M years ago, Homo erectus (upright man) appeared, bigger and brainier (850 to 1,100 cm³) . They were the first humans to leave Africa, as their remains have been found mostly in Indonesia and China. They, in turn were replaced by an out of Africa wave of modern humans some 70- 30 kya. H. erectus produced a more “advanced” stone technology, the “Acheulean” and also learned to use fire.

Acheulean stone tools were also flakes knocked off a core, but these flakes were reworked several times, chipping their edges, to produce a sharp blade. The worked core resulted in a pear-shaped “axe”. The working of the core produced tools which were more symmetric than the Oldowan ones.

The H. erectus stock that remained in Africa is known as Homo ergaster (working man)kept on evolving, producing a group that left Africa and peopled Europe via the Middle East, the H. heidelbergensis (Heidelberg man – where its remains were first found, in Germany), who then evolved ino H. neanderthalensis (After the site of Neanderthal in Germany).

Those that remained in Africa continued evolving, becoming Homo Sapiens, (wise man), modern humans.

The changing picture

That was the neat former picture, but science evolves with new findings at new sites and novel techniques (genetic ones) which have somewhat altered it. Fossils found in Spain, Georgia and Russia plus genetic analysis of hominid remains have redrawn this nice picture.

To make it worse, you should bear in mind that there is little consensus among scholars regarding the relationship between all these hominids as dates are sometimes uncertain or, the fossil evidence is lacking.
Anyway, as I am not a scholar I can allow myself to speculate freely!

Dmanisi hominid

A variety of human dating to 1.75 M years ago, it is also known as Homo georgicus, (Man from Georgia – where it was found). Their small brain size and rounded shape of their skulls places them closer to H. habilis than to H. erectus, and their discoverers wrote:

We suggest that the ancestors of the Dmanisi population dispersed from Africa before the emergence of humans identified broadly with the H. erectus grade.[3]

Furthermore, their tools were “Oldowan” [4] (“primitive”).

Did H. habilis leave Africa first?

The discoverers of Dmanisis suggest that these hominids are a variety of Homo habilis that left Africa, crossed the Middle East and moved on into the Caucasus (Europe and Asia) about 2 M years ago. If so, they were the first “humans” to do so.[2]

H. erectus originated in Asia

They also suggest that the Homo habilis “Dmanisi” evolved in Asia, becoming an “early” variety of H. erectus.[2]

And now things get interesting: they split into different branches of H. erectus, some stayed in Asia and walked east, the ancestors of later Java and Peking men (the H. erectus remains found in Indonesia and China). Others went back, south and returned home to East Africa, originating a more slender African erectus, H. ergaster, who would eventually give rise to us, modern humans.[2]

The map below shows the path out of Africa (from Olduvai gorge) towards Georgia (Dmanisi) of our tiny African H. habilis with his Oldowan tool industry (Red arrow).

At Dmanisi they evolved into H. erectus, who acquired the Acheulean stone tool technology and took it with them back to Africa, but, surprisingly they did not take it along with them in most of their journeys:

• Eastwards into China and Indonesia (no tools found in Java though, perhaps they used bamboo cane for their tools). Their bones have been recovered from the sites at Sanigran (1.66 M years ago) and Yuanmou Man (1.7 M years ago) , and their tools at Nihewan (1.65 M years ago) however they were “more comparable to Oldowan localities in Africa”. Close to Beijing, later H. erectus remains have been found but the only Acheulean tools found in China are much more recent (ca. 800 kya). Pale blue arrows across southern Asia.
• West, into Europe, where H. antecessor was found in Spain (Sierra de Atapuerca) where they lived between 1.2 M years ago and 780 Kya. They also used “Oldowan” tools (perhaps they moved west before acquiring the Achulean know-how?). Pale blue arrow through Europe.
• A third group walked back, through Israel (Ubeidiya site’s Acheulean tools 1.5 M years old) into Africa, across the north (Algiers site at Ain Hanech 1.8 M years ago with “Advanced Oldowan tools”.) the rest moved south back towards East Africa. Pale blue arrows into Africa.

Map showing the possible dispersion of H. habilis across the globe.
Copyright © 2011 by Austin Whittall

Hobbits and American ape men

The minute Flores Island “hobbit”, Homo floresiensis is also more primitive than h. erectus, which leads us to ask: Was he the outcome of an H. habilis group that split from those moving north, and migrated east, into South East Asia and Indonesia?

And, for us, keen on finding out more about the possible origin of our Patagonian ape-like creatures, could tiny H. habilis have kept on walking across Asia and reached America via Bering? (both the Hobbit route and the American path are shown with green arrows in the map above).

There is some evidence of human presence in the Indian Subcontinent: “hominid-struck stone artefacts [...] ca. 2 million years old”[1] In artifacts near Riwat, northern Pakistan, on the Indo –Gangetic floodplains. No bones have been found, so it is not possible to identify their makers, but we know that they are “Oldowan” so they are pre-H. erectus.

Similar tools have been found in China, and date back to 2 M years at Renzidong in Anhui, Eastern China. But, again, human bones are lacking.

So we have ancient human presence in India and China, 2 million years old, contemporary to the H. habilis out of Africa event. These probably kept on moving into America (the north group) and to the southernmost island, at Flores.

Archaic modern men

There is a clear differentiation between those “primitive” H. erectus, H. ergaster and H. antecessor and the more “modern” variety that later spread out across Africa, Europe and the Middle East. The latter had a larger brain, and have been found at different sites.
The transition between both “varieties” is unclear because the period covering it (1,000 to 600 kya) is not very abundant in hominid fossils all across the Old World.

We know that something happened at that time, we are not quite sure where it happened, but the outcome was a brainier mankind.

• Europe . H. heidelbergensis. Their remains at Atapuerca, Spain date back to about 600 kya. Their tools are Acheulian. Where they replaced the H. antecessor people. They had Acheulean assemblages. They are also found at Heidelberg and Steinheim (Germany), Arago (France), Petralona (Greece), Sima de los Huesos (Spain), Boxgrove (UK) and Ciampate del Diavolo (Italy).
• Africa. Bodo and Kabwei sites (which some group within Homo rhodesiensis).
• Asia. Dali and Jinnishuan in China

Some 300 kya, they gave rise to Neanderthals in Europe and the Levant, and Modern Humans in Africa some 150 – 200 kya. But there is another mysterious group, the Denisovans:

Denisovans

The site located in Altai, Russia, produced a fossils of a new species of hominids. The Denisovans.

These Denisovans differ from both H. neanderthalensis and H. sapiens but share a common ancestor with them about 1 M years ago. The Denisovans may represent an unknown homind that left Africa and originated the human and Neanderthal ancestors. They managed to survive until 40 kya.

Using DNA extracted from a finger bone found in Denisova Cave in southern Siberia, we have sequenced the genome of an archaic hominin to about 1.9-fold coverage. This individual is from a group that shares a common origin with Neanderthals. This population was not involved in the putative gene flow from Neanderthals into Eurasians; however, the data suggest that it contributed 4–6% of its genetic material to the genomes of present-day Melanesians. We designate this hominin population ‘Denisovans’ and suggest that it may have been widespread in Asia during the Late Pleistocene epoch. A tooth found in Denisova Cave carries a mitochondrial genome highly similar to that of the finger bone. This tooth shares no derived morphological features with Neanderthals or modern humans, further indicating that Denisovans have an evolutionary history distinct from Neanderthals and modern humans [5]

The paper also showed that Neanderthal and modern humans share a common ancestor 800 kya and that they split apart between 270 and 449 kya. The Neanderthals and Denisovans diverged 604 kya and 804 kya from modern humans.[5]

A possible cause for these exceptional genetic traits in Denisovan remains of people who lived 30 to 50 kya, may be the following:

• Denisovans retained features that Neanderthals and humans lost
The Denisovans acquired them from "some even more diverged hominin[5] that is, extant out of Africa H. habilis or their later descendants.
• Reversal to ancestral traits.

The molar that was recovered from a Denisovan shows that it was much larger than those of early modern humans and Neanderthals but similar to those of H. erectus and H. habilis. Could they be some relict descendants of H. habilis?

Denisovan, Neanderthal and humans.From [7]

The Image above is “Phylogenetic tree” adapted from Paabo.[7] The actual dates are 1.3 Mya – 779 kya for the divergence between Denisovans and Neanderthal / Humans, and 321 – 618 kya (mean 466 kya) for the Neanderthal – Sapiens cleavage.

Though some disagree [6] and interpret the data differently.

The HLA-B*73 allele and Denisovans

Human leukocyte antigens (HLAs), are a family which has roughly 200 genes which are crucial for our survival as they allow our bodies to fight off diseases. They make up our immune system. They are also among the most variable of human genes: there are hundreds of variations (known as alleles) of each of these genes in the human population. And thanks to them, we are tweaked to react to different diseases and adapt to new ones.

Modern humans walking out of Africa in small groups had, most likely a very limited quantity of HLA alleles, and these were specially adapted to those diseases found in Africa.

When these modern humans reached Asia, with two million years of parasite-human host adaptation, between the first waves of hominids leaving Africa and the native Asian disease agents, they were in deep trouble. But, if they “mingled” (i.e. mated) with a native Asian hominid population, their offspring would have inherited Asian HLAs, well adapted to indigenous diseases.

A study has proven just that, and guess who passed on the HLAs to modern humans? Yes, the Denisovans (below is an abstract from a paper –bold face mine):

Whole-genome comparisons identified introgression [genetic input] from archaic to modern humans. Our analysis of highly polymorphic HLA class I, vital immune system components subject to strong balancing selection, shows how modern humans acquired the HLA-B*73 allele in west Asia through admixture with archaic humans called Denisovans, a likely sister group to the Neandertals. Virtual genotyping of Denisovan and Neandertal genomes identified archaic HLA haplotypes carrying functionally distinctive alleles that have introgressed into modern Eurasian and Oceanian populations. These alleles, of which several encode unique or strong ligands for natural killer cell receptors, now represent more than half the HLA alleles of modern Eurasians and also appear to have been later introduced into Africans. Thus, adaptive introgression of archaic alleles has significantly shaped modern human immune systems.[8]

Now this is really interesting, moreso because this HLA-B*73 allele is not very common and appears at very low frequencies among the modern human population.
But this post has got too long! Next post will look into the B*73 and its current global distribution (yes, it is found in America, but in very strange locations, and with very odd natives! Also it is found in ... Altai, the Denisovan enclave and the Middle East, home to the Druze, which also are linked to America... but more in my next post).

Sources
[1] R. W. Dennell, H. M. Rendell and E. Hailwood, (1988). Late Pliocene Artifacts from Northern Pakistan. Current Anthropology. Vol 29, No. 3. Jun. 1988. pp. 495-498.
[2] John g. Fleagle. Out of Africa. pp 249 – 277
[3] Abesalom Vekua, David Lordkipanidze et al. (2002). A New Skull of Early Homo from Dmanisi, Georgia. Science 5 July 2002: Vol. 297. no. 5578, pp. 85 - 89 DOI: 10.
[4] Deborah Barsky, (2009), An Overview of Some African and Eurasian Oldowan Sites: Evaluation of Hominin Cognition Levels, Technological Advancement and Adaptive Skills. In Interdisciplinary Approaches to the Oldowan . Vertebrate Paleobiology and Paleoanthropology, 2009, 39-47, DOI: 10.1007/978-1-4020-9060-8_4
[5] Reich, David, et al. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia
Nature 468, 1053–1060 (23 December 2010) doi:10.1038/nature09710
[6] Caldararo, Niccolo and Guthrie, Michael. A Note On The Denisova Cave mtDNA Sequence. Available from Nature Precedings (2011).
[7] Krause, Johannes; Fu, Qiaomei; Good, Jeffrey; Viola, Bence; Shunkov, Michael; Derevianko, Anatoli and SvantePääbo. (2010) The complete mithocondrial DNA genome of an unknown hominin from southern Siberia doi:10.1038/nature08976. Letters. Nature 464, 894-897 (8 April 2010)
[8] Abi-Rached, et al. (2011). The Shaping of Modern Human Immune Systems by Multiregional Admixture with Archaic Humans Science 25 August 2011: 1209202DOI:10.1126/science.1209202

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