Neanderthal and Denisovan ancestors may have interbred with Superarchaic humans, research suggests.
A software approach to exploring human evolutionary history has shed light on a discrepancy between genetic evidence from fossils excavated from Sima de los Huesos in Spain and a 2017 model developed by the same researchers.
The model indicated Neanderthals split from Denisovans about 381,000 years ago.
However, a new study published in Science Advances suggests they separated much earlier, implying Neanderthals were already distinct from Denisovans by 600,000 years ago.
The research also reveals that the ancestors of Neanderthals and Denisovans interbred with members of a “superarchaic” hominin population – the earliest reported episode of gene flow.
The new model supports the view that modern humans and their ancestors expanded from Africa into Eurasia only three times – 1.9 million years ago; 700,000 years ago; and 50,000 years ago.
Large-brained hominins first appeared in Europe and Asia about 600,000 years ago in the period known as the middle Pleistocene – an important milestone for early humans.
To shed light on this period in human evolution and to uncover the missing pieces from their previous model, Alan Rogers et al considered eight models with various genetic combinations that may have resulted from interbreeding between early hominins.
They included data from Neanderthals from the Altai Mountains of Siberia and the Vindija Cave in Croatia, as well as from modern Europeans.
Researchers analysed the data using software designed to focus on the deep past.
Lead researcher Alan Rogers said: “We’ve never known about this episode of interbreeding and we’ve never been able to estimate the size of the super-archaic population.
“We’re just shedding light on an interval on human evolutionary history that was previously completely dark.”
He added: “Our Legofit software ignores the within-population component of genetic variation.
“For this reason, it is unaffected by recent changes in population size, which often interfere with efforts to study deep history.
“In effect, we have cleared away some of the brush that often obscures the view of the distant past.”