Regardless of how they communicated, their encounters led to breeding between both species. How this occurred remains a mystery.
Was the interbreeding a success?
Whether or not the interbreeding was a success depends on the breeding pair. There is no evidence of Homo sapiens genetics in late Neanderthal genomes from 40-60,000 years ago.
Even though we know that our species interbred with Neanderthals, the genes we have in us today aren’t a result of the interactions that Homo sapiens maintained when they left Africa.
Another interesting finding – the lack of mitochondrial DNA, which is inherited through females point to the evidence that only male Neanderthals and female Homo sapiens could mate.
“We don’t know if the apparent one-way gene flow is because it simply wasn’t happening, that the breeding was taking place but was unsuccessful, or if the Neanderthal genomes we have are unrepresentative. As more Neanderthal genomes are sequenced, we should be able to see whether any nuclear DNA from Homo sapiens was passed on to Neanderthals and demonstrate whether or not this idea is accurate,” added Stringer.
Evidence suggests that the Neanderthal and Homo sapiens lineages began diverging about 600,000 years ago, evolving largely separately in Eurasia and Africa after that time. Around 60,000 years ago H. sapiens began a significant emergence from Africa that would lead to a near-global distribution by 10,000 years ago. However, recent research on fossils from Apidima Cave (Greece) suggests that there was an earlier dispersal of our species that reached Europe more than 200,000 years ago, which is consistent with data from ancient DNA suggesting gene flow between the early H. neanderthalensis and H. sapiens lineages during the time span of the later Middle Pleistocene. Additional range expansions of H. sapiens are suggested from western Asian evidence prior to 100,000 years ago, and from China, Sumatra and Australia before the 60,000-year datum. Until recently, there were few other signs of a H. sapiens presence in Europe prior to the Aurignacian expansions that began around 41,000 years ago. However, new data from sites like Zlatý k?? (Czechia), Bacho Kiro Cave (Bulgaria), Grotta del Cavallo (Italy) and Grotte Mandrin (France) indicate that there were pre-Aurignacian dispersals that potentially placed H. sapiens populations alongside the persisting Neanderthals. While some of these populations can be related to later Eurasians, others seem to represent now-extinct lineages of H. sapiens. It is now known from a growing body of genetic data that this co-existence of H. neanderthalensis and H. sapiens was accompanied by bouts of interbreeding between the two species. It is suggested here that a continuing absorption of Neanderthal individuals into H. sapiens groups could have been one of the factors that led to the demise of the Neanderthals.