Mapping Human Evolution Out of Africa

Neanderthal

Out of Africa; new research explores drive behind early humanity's travels across the world - Royal Holloway, University of London

Interesting news came a few days ago from Royal Holloway, University of London, that a new research project is to start next month, aimed at mapping the spread of humans out of Africa and across the globe, to occupy all major landmasses other than Antarctica. The research is financed by a £450,000 grant from Leverhulme Trust.

As the Royal Holloway press release says:

Over the next three years the team led from the Department of Geography at Royal Holloway will examine important archaeological and environmental sites across the Levant and Arabian Peninsula to understand when and why early humans travelled from Africa, a movement that saw humans dominating the globe.

Working in close collaboration with expert archaeologists and scientists from across the region and also from leading research centers in Europe, the research will seek to resolve uncertainties about the chronology of early human dispersals Out of Africa.

Searching for clues in ancient volcanic ash

New environmental and archaeological information coupled with genetic evidence will help uncover the drivers behind the global distribution and dominance of our species. The team will investigate the role of factors such as environmental changes and species interbreeding in spreading humanity across the world.

“Current thinking suggests that humans started moving out of Africa over 120,000 years ago,” explained Professor Simon Blockley of Royal Holloway’s Department of Geography who is leading the project.

“For the first time in this region we will be using a state-of-the-art method for dating events by finding microscopic traces of volcanic ash within archeological and environmental sites that can then be linked to known and dated eruptions. This ash will contain clues as to the timing of the dispersal of human groups and any climatic triggers behind them,” he concluded.

The project is a collaborative effort including Michael Petraglia of the Max Planck Institute for the Science of Human History, Simon Armitage of Royal Holloway and Professor Chris Stringer of the British Natural History Museum begins July 1, 2017.

Homo erectus

Source: Wikipedia

Hopefully, the project will also deal with the confusing evidence caused by there being, frankly, too many archaic hominid fossils showing transitional features between the early African hominids as they emerged from the Australopithecines. The current consensus it that an Australopithecines evolved into Homo habilis, possibly via an as yet undiscovered intermediate and that the other hominids evolved from this basal species.

Here is where consensus begins to break down, however, partly because of the way fossils which don't fit easily into species already described are given the status of a new species. Was H. erectus, generally assumed to be the founder species of most of the other hominids and the first to leave Africa, a different species to H. habilis or a subspecies? Was H. ergaster an intermediate between H. habilis and H. erectus or a sister species? And where does H. naledi and Au. sediba fit in this model?

Then we have a plethora of hominids that are assumed to have evolved from H. erectus such as H. rudolfensis, H. antecessor, H. heidelbergensis, H. neanderthalensis, the 'Denisovans' and, of course H. sapiens or modern humans. Some of these might have evolved in Eurasia or in Africa and then migrated out. The large number of hominid skulls found in Dmanisi in Georgia in the Caucasus are assumed to be those of H. erectus but show such a range of forms that would encompass H. heidelbergensis, H. rudolfensis, H. rhodesiensis and H. antecessor and even H. habilis.

Homo heidelbergensis

Source: Wikipedia

So, did we once have a wide-ranging variable species, evolving locally because of local isolation but then hybridising later with other sub-species when contact was established. In other words, the archaic hominids may have been behaving very much like a ring species, tending to diverge but never becoming isolated enough to evolve into separate species. Were there once several co-existing human species, especially in Africa, more than one of which migrated out? And who made those undoubtedly hominid footprints on the Norfolk coast 900,000 years ago, before modern humans evolved?

We know from DNA analysis that H. sapiens, H. neanderthalensis and the 'Denisovans' (? H. altai, H. neanderthalensis altai or H. erectus altai) interbred occasionally and that some populations in South East Asia and Melanesia have some Denisovan DNA as well as some Neanderthal, as do all non-African modern humans (and some African populations, because migration was not always a one-way process).

We also know that interbreeding between early moderns and Neanderthals did not produce stable hybrid populations because of the absence of both Neanderthal Y chromosomes and Neanderthal mtDNA in the modern genome. This suggests that the only viable hybrid offspring were female children with a Neanderthal father and a modern mother. What we don't know is whether the children of a modern father and a Neanderthal mother were viable, fertile or sterile since with the small number of Neanderthal genomes analysed so far, we just might not have found any with modern Y chromosomes of mtDNA. But the partial barriers to hybridisation are sufficient to place Neanderthals and moderns in different species.

Hopefully, this exciting project will answer some of these questions and help clarify what is currently a confusing picture, especially of the migrations out of Africa and how, when and where the emerging modern species interbred with earlier migrations by archaic hominids. One thing it will undoubtedly not reveal is that all humans are descended from a single couple who had no daughters (No! There really are people who believe that!) or even from eight survivors of a global flood who got off a boat in Turkey.

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