An article published in the journal “Nature Genetics” reports the results of a sophisticated genetic research that concludes that the species Homo sapiens is the result of the crossbreeding between two populations belonging to different species of hominins. Trevor Cousins, Aylwyn Scally, and Richard Durbin of the British University of Cambridge developed a genetic analysis software called cobraa to create models of ancient human populations splitting apart and merging back. The application of cobraa to the genetic data obtained from modern humans from all over the world indicates a split between two populations dating back to about 1.5 million years ago to a crossbreeding between their descendants about 300,000 years ago. The two species could be Homo erectus (Bottom photo ©Peter Maas) and Homo heidelbergensis (Top photo ©Jonathan Cardy) but for now, these are hypotheses.
The reconstructions of the history of humanity conducted in recent decades are increasingly showing crossbreedings between different populations and even very ancient migrations. The reconstructions become much more complex when trying to reconstruct the origin of the species Homo sapiens. Several studies have challenged the idea that modern humans evolved from a single African population, perhaps Homo heidelbergensis. Now, three Cambridge researchers offer a genetic interpretation of that idea.
This study was based on DNA from people who participated in the 1000 Genomes Project, a global effort to sequence the DNA of populations living on different continents. The Cambridge researchers ran the cobraa genetic software they developed to model genetic split and merge in ancient human populations on these genomes, which represent all of humanity.
The results of the genetic analysis conducted with the cobraa algorithm offer a new reconstruction of the possible origin of the species Homo sapiens. In this scenario, two hominin species diverged about 1.5 million years ago. Soon after, one of the two populations went through a population bottleneck, a drastic reduction in population followed by slow growth over the course of about a million years. This population contributed 80% of the DNA of Homo sapiens while the other population contributed 20% in a crossbreeding that occurred about 300,000 years ago.
To put this into perspective, modern Europeans have about 2% of Neanderthal genes derived from crossbreedings that occurred over millennia. This means that the genetic contribution indicated in this new study was much more substantial and sufficient to create a new species.
Fossil evidence suggests that the two populations indicated by this genetic study may be Homo erectus and Homo heidelbergensis because both were present in Africa at the time of the alleged crossbreeding that led to the birth of Homo sapiens. However, we don’t have DNA from any individuals belonging to these two species, which makes it even more important to continue the studies first to test the conclusions of this genetic analysis and, if confirmed, look for evidence regarding the ancestors of Homo sapiens.
The species Homo heidelbergensis has been considered as the ancestor of Homo sapiens and Neanderthals, but there have been various controversies regarding this hypothesis. This species has sometimes been considered a subspecies of Homo erectus and sometimes an archaic form of Homo sapiens. The attribution of some fossils to Homo heidelbergensis is also controversial, confirming the difficulties existing in reconstructing the history of humanity with the various species of the genus Homo that existed over time.
The species Homo bodoensis was proposed in 2021 as a direct ancestor of Homo sapiens, also including the fossils attributed to the species Homo heidelbergensis. However, at least for now, the discussions that followed that proposal have offered mainly negative reactions.
Considering only the genetic reconstructions of the history of humanity, this study offers different conclusions than those obtained by other researchers published in the journal “Nature” in May 2023. In that case, too, confirmations were offered of the so-called multiregional thesis of different populations at the origin of the species Homo sapiens but with a different timeline. This new study indicates a decidedly older remixing so actually, both studies could be at least partially right.
All this continues to show the complexity of the history of humanity. Migrations of populations of various species are certain and evidence of interbreeding between different populations, even classified as different species, is emerging from various studies. Reconstructing these merges is still really difficult despite the progress in genetic techniques but developments in this type or research are arriving in small steps.
