Research Fellow João Teixeira will commence his DECRA fellowship at ECDI in the second half of 2021, as he returns to Australia from his native Portugal. João’s academic interests lie in the demographic and adaptive history of the human species. By analysing the DNA of contemporary populations from Indonesia, New Guinea and Australia, João’s DECRA research will seek to further clarify when and where the first human encounters with extinct hominins across this vast geographical region occurred.
João was drawn to ECDI because of the initiative’s deep commitment to transdisciplinarity. Coming from a background in natural science, in particular biology and genetics, João has spent much of his career investigating the genetics of hominid evolution. As a PhD student at the Max Planck Institute for Evolutionary Anthropology, in Germany, João studied how natural selection maintains advantageous genetic diversity for millions of years in humans and their closest living relatives, the great apes. His recent post-doctoral work at the Australian Centre for Ancient DNA at the University of Adelaide has applied a focus on ancient DNA to study the admixture events between human groups in the Pleistocene, and the genetic history and historical migrations of people in Europe and the Americas. While at ECDI, João will continue to focus on the early encounters between human groups in Island Southeast Asia, adopting a truly multidisciplinary scope by combining insights drawn from genetics with archaeological, anthropological and linguistic research.
“Throughout my entire career I’ve been working with geneticists and devoted a lot of attention to this topic,” João explains. “I believe that my background offers a different perspective that archaeology or anthropology cannot capture, because genetics represents a different tool offering complementary answers. However, these answers remain incomplete.”
“We’re now at a point where truly meaningful questions require a transdisciplinary lens,” he continues. He is following through on this ethos already, and together with Ray Tobler recently co-authored a paper with ECDI colleague Shimona Keely, who similarly investigates ancient human migration, but from an archaeological perspective.
For his DECRA, João will undertake computational and statistical analysis of contemporary genetic data. He is particularly interested in tracing genetic markers of an ancient group of humans called the Denisovans. Denisovans are a species of the Homo genus, related to contemporary humans (Homo sapiens) and Neanderthals. Of the few Denisovan fossil specimens that exist, most have been discovered in mainland Asia (Siberia and the Tibetan Plateau). Archaeologists have dated these specimens to be tens of thousands of years old. A sister group to Neanderthals, Denisovans are now also considered extinct.
João, however, prefers not to see them in this light. He sees the Denisovan and Neanderthal lineages as surviving in the living descendants of early encounters between these groups and modern human populations migrating out of Africa.
“We like to think of Neanderthals and Denisovans as extinct, and ourselves as the survivors. It is true that those populations that lived in the Pleistocene are extinct. But that is also true for the early modern human populations that left Africa 60,000 years ago. However, everyone alive today has inherited genetic ancestry from all of these groups, and without them we would not be here. So they survive through us.”
The lands of Island Southeast Asia and Oceania are where contemporary human populations contain the highest amount of genetic ancestry from the Denisovans. Between 4–6% of the DNA of Indigenous Australians, Papuans and other traditional inhabitants of the region contain markers of Denisovan ancestry. This proportion is much larger than observed in mainland Asia (~1%) and suggests that a separate group of Denisovans settled in Island Southeast Asia and Oceania.
That is at least what previous work by João and others suggests. What João wants to investigate with his DECRA fellowship is whether the concentration of Denisovan-derived DNA in contemporary populations indicates multiple admixture events with island-dwelling ancient Denisovans.
“In this project, I aim to disentangle the complex patterns of Denisovan admixture with incoming populations of modern humans from Africa and Eurasia.”
João will measure the concentration of Denisovan DNA in contemporary populations. Then, using statistical models that project the concentration and distribution of DNA backwards through history, he will estimate how this genetic material passed from one generation to the next as different human groups interbred. This will lead him to an approximation of when these groups first encountered each other in the region. He intends to compare his findings with archaeological data to refine our understanding of human movement and evolution in Island Southeast Asia and Oceania.
In addition, João wants to understand whether some of the Denisovan genetic material has helped contemporary populations adapt to local environmental conditions in Island Southeast Asia.
“We know that Denisovan variants have helped humans adapt to life in high-altitude environments, but there are likely other instances in the genome of contemporary people where Denisovan genetic variants helped us survive and adapt to local conditions. The amount of Denisovan DNA in contemporary people and the heterogeneous environments of Island Southeast Asia, New Guinea and Australia make this a particularly interesting setting.”
Finally, João thinks that some of the currently known fossil specimens from the region might be Denisovans ‘disguised’ as other hominin species that are thought to have split earlier from the human lineage.
“It would be amazing to be able to determine the location of the local admixture events between Denisovans and modern humans. It is possible that some of these events occurred in islands that are home to fossil specimens thought to belong to other groups.”
He is referring to fossils of Homo erectus in Java, H. floresiensis in Flores and H. luzonensis in the Philippines, all of which are thought to represent groups that split from modern humans much earlier than Denisovans. However, João is not completely convinced about the presumed identity and relationship between some of these fossils and modern humans.
“We have no DNA available for any of these specimens and their placement in our family tree is mostly based on morphological comparisons. And a growing amount of evidence shows Denisovans inhabited the region but their fossils are yet to be found. If we show that some admixture events have occurred in the home islands of these fossils, then we may have to reconsider our current classification of these fossils. That is why we need to integrate findings from different scientific disciplines.”
As with most research since the start of 2020, the pandemic has disrupted João’s plans. He was intending to conduct fieldwork in remote areas of Indonesia and PNG, but with travel to these communities currently out of the question, his team will instead rely on data gathered by collaborators in Indonesia. João nevertheless hopes to expand the research scope to include PNG and Australia in the near future and maintains a strong desire to work with the Indigenous people of the region. “We want to integrate ethics and the local and Indigenous people, because at the end of the day, we are trying to understand their history. So our work is part of their heritage and belongs to them.