The history of our ancestors is becoming increasingly complex. Because now, in genetic analyzes, researchers have found evidence of another cross between earlier human species. Accordingly, the common ancestors of the Neanderthals and Denisova people crossed around 700,000 years ago in Eurasia with a “superarchaic” early human form. If this is confirmed, this would be the earliest known mix of different human species to date – and the fifth known episode of such mating between species. In addition, the results suggest that the tribal lines of Neanderthals and Denisova people separated earlier than previously thought.
The history of mankind is a story of parallel tribal lines and affairs: Again and again there were different kinds of people, some of whom lived in the same place at the same time and also mated with each other. At times, our family tree is more like a confusing scrub than a classic pedigree. To make matters worse, many of the primeval human variants have hardly been researched because anthropologists only conclude their existence from isolated findings or genetic evidence. So far, it seems clear that around 800,000 years ago our lineage separated from that of the common ancestor of the Neanderthals and Denisova people. These, in turn, developed into separate species after 390,000 years ago. However, this time estimate is not without controversy, since some DNA analyzes recently separated these two lines much earlier.
Mating between archaic homo and “Neandersovans”
In this context, Alan Rogers and his colleagues from the University of Utah have once again looked for genetic evidence of separations and crossings of earlier human lineages. They use an algorithm to specifically identify characteristic DNA signatures of archaic human species in the genome of two European populations and as a reference population for the Yoruba people from Africa. The already decoded genomes of the Neanderthals and Denisova people also used them for comparisons. In addition, the researchers used the technology of the molecular clock to infer the timelines and the age of certain genetic parts via the mutation rate of our genome. The focus of the gene analyzes was on the time around 600,000 years ago. “We are shedding more light on an interval in human history that was previously completely dark,” says Rogers.
The evaluations gave surprising results. Because according to the DNA analyzes, the common ancestors of Neanderthals and Denisova people – called by the researchers Neandersovaner “- must have crossed with a” superarchaic “kind of people in Eurasia around 700,000 years ago. “This is the earliest known mix between different types of people,” Rogers and his colleagues report. According to their statistical-genetic calculations, the superarchaic human species must have separated from the family tree of the other human species almost two million years ago. The researchers do not specify what species within the Homo genus it is, whether the Homo erectus is an option. However, they determined that this population must have comprised between 20,000 and 50,000 individuals at that time.
Crossings, migration and species separations
If this early cross between superarchaic people and the common ancestors of the Neanderthals and Denisova people were confirmed, this would also be a special feature in other respects: the partners belonged to tribal lines that had been separated from each other for 1.2 million years – that’s a long way off longer than with any other known cross between different types of people. “It also tells us a lot about how long it takes for a reproductive barrier to develop between species,” says Rogers. Overall, he and his team found evidence of five episodes of interspecific crosses among the examined representatives of the genus Homo. Two of these occurred between Homo sapiens and Neanderthals, one between Neanderthals and Denisova people, one between Denisova and an archaic human species, and the last, earliest between the superarchaic representative of the Homo genus and the common ancestors of Neanderthals and Denisova people.
However, the genetic analyzes could also shed new light on the settlement history of Eurasia. Because, according to the calculations by Rogers and his team, representatives of the Homo genus should have moved from Africa to Asia in three batches. “The first was an expansion of early homo around 1.9 million years ago, then that of Neandersovans around 700,000 years ago and finally the emigration of modern humans around 50,000 years ago,” said the researchers. According to their interpretation, the Neandersovans settled Eurasia around 700,000 years ago, then met the indigenous people there in the form of the superarchaic people and soon split up into the Neanderthals and Denisova people. According to the new genetic data, this split could have happened much earlier than previously thought: “According to our estimates, the Neanderthals were a separate line of tribe 600,000 years ago, separated not only from Homo sapiens but also from the Denisova people,” report Rogers and his colleagues.
Source: Alan Rogers (University of Utah, Salt Lake City) et al., Science Advances, doi: 10.1126 / sciadv.aay5483