By John Kerr 22/09/2016

Where did we come from and when did we leave there? These existential questions are at the heart of several human genetics studies published today in the leading journal Nature, all with links to New Zealand.

Tracing our genetic roots

The now widely accepted ‘Out of Africa’ hypothesis puts Africa as the origin of all modern humans. However, there is still debate over exactly when the first humans left the continent and started to spread elsewhere around the globe.

Some theories suggest that all present-day non-Africans can trace their ancestry back to a single population while others infer that migration out of Africa took place in distinct waves at different times.

One of the new Nature papers, co-authored by Massey University Professor Murray Cox, adds fuel to the debate by uncovering genetic evidence of an early and now largely extinct wave of humans. The researchers’ analysis suggests this population moved from Africa to Eurasia between 100,000 and 120,000 years ago – contrary to research suggesting all non-Africans trace their ancestry back to a single migration event around 40,000 to 75,000 years ago.

An earlier wave of migration out of Africa? Prof Murray Cox. Massey University.
Prof Murray Cox. Massey University.

The genetic remnants of this early exodus are not found in the DNA of most humans, but the secret lay in the genomes of modern Papuans (the indigenous people of Papa New Guinea), which revealed at least two per cent of their genetic material is retained from this earlier population.

“The study is able to provide some remarkable results and puts forward a strong case for more investigations into the DNA of smaller, more remote ethnic groups,” Professor Cox says.

“These are under-explored regions from a genetic standpoint, as traditional studies have focused mainly on the standard categories of Europeans, Asians and Africans. While these have been a treasure trove of knowledge of our early movements and makeup, it’s now time to cast the net wider and discover what these other regions have to tell us.”

Read more about the research on Scimex.

Out of Africa: Conflicting results

Capturing genetic data from smaller ethnic groups is also the focus of a second paper in Nature, detailing results from the Simons Genome Diversity Project. This research analysed high-quality genome data from 300 people from 142 different populations usually under-represented in large-scale studies, including New Zealand Māori, to fully investigate the range of human genetic variation.

This study’s findings tell a slightly different story, with the authors concluding that New Guineans (and indigenous Australians) do not derive substantial ancestry from an early dispersal of modern humans; instead, their modern human ancestry is consistent with coming from the same source as that of other non-Africans.

These findings aligned with third paper in Nature describing the first extensive survey of human genetic diversity in Australia — a poorly studied region that, together with New Guinea, contains some of the earliest archaeological and fossil evidence of modern humans outside Africa. According to this DNA analysis of 83 Indigenous Australians, ancestors of Aboriginal Australians and Papua New Guineans diverged from Eurasian populations between 51,000 and 72,000 years ago.

Lisa Matisoo-Smith, one of the co-authors and Professor of Biological Anthropology, Department of Anatomy, University of Otago, was excited by the findings and highlighted the importance of undertaking a collaborative and respectful approach in research indigenous populations:

“It sets a standard for the collaboration of geneticists, archaeologists, linguists and Aboriginal elders and community representatives,” she said in a release.

“It demonstrates how western science and traditional knowledge can be complementary and collaborative.”

Co-author Professor Eske Willerslev, from the University of Copenhagen, outlines their findings on the genetic history of Indigenous Australians in the video below:

More details about these studies can also be found on Scimex.

Riddle far from solved

However, Prof Cox’s research noted above hints that DNA from the mysterious first wave population of humans leaving Africa also somehow made its way in to the genetic mix of the modern Papuans. Thus in some ways these newly published studies raise more questions than they answer.

“The high-resolution portrait of human genetic diversity afforded by these studies allows new inferences to be made about our migration out of Africa,” write US genetic researchers Serena Tucci and Joshua Akey in an accompanying Nature News & Views article.

“Although these studies fill in some missing pieces in the puzzle of human history, many fascinating questions remain…to fully retrace the steps taken by our ancestors as they explored and colonized the world.”