After writing a post on this subject a few days ago along comes Chris Catling with his thoughts on the subject in Current World Archaeology 126, August 2024, pages 62 and 63. A fascinating subject – but is something amiss. He says that looking at brain and skull shape alone highlights a difference between archaic and modern humans, as can be seen even in the new Cambridge University reconstruction of the face of a Neanderthal woman. This was done to demonstate the species was not ‘brutish’ or ‘unsophisticated’, as the older view of Neanderthals back in the day. Shanidar Z was one of 10 excavated in 2018 from a cave in Kurdistan. Reconstructing her face involved piecing together the 200 pieces of her skull – which looks very different to modern human heads. For example, it has large brow ridges and a projecting mid face that results in a more prominent nose. However, she is not too different in other ways from modern humans, which may account for the interbreeding. In fact, the reconstruction suggests these differences were not as glaring in real life.
This takes Catling to the missing Y chromosome – why no Neanderthal DNA has been found in the Y chromosomes of modern men, despite the fact that people across Euroasia, and north of the Sahara, have inherited between one and four per cent of their genome from Neanderthals. Preumably this is found in the female genetic line. According to a 2016 study this could be the result of genetic drift on the basis genes can die out in small or isolated populations. They also allow mutations to occur, some of which are not beneficial. The Y chromosome can only be passed on by father to son.
When did interbreeding take place? Quoting from a paper at https://doi.org/10.1101/2024.05.13.593955 … that informed us that Neanderthal genes in people alive today all date from admixture that is thought to have taken place between 47,000 and 40,000 years ago, coming to an end when Neanderthals became extinct. This period, we may note, also includes the Lachamp Event and a mixture of old C14 dates and more recent C14 dates. This probably caused the time lapse of 7 or 8 thousand years. Apparently, these Neanderthal and modern human interbreeding episodes prior to Laschamp to not seem to have passed on genes into modern humans after Laschamp. They only passed on the Neanderthal genes immediately prior to Laschamp. So, were the earlier modern humans in the fossil record, really modern humans, or only hominems with a different skull shape? As the remains are fragmentary that is only a possibility. Scientists are convinced that interbreeding episodes did exist – during the last Interglacial period, as an example. The general opinion now is that interbreeding probably took place on numerous occasions – as people moved Out of Africa. The problem is that DNA from these earlier migrations have not been passed on to succeeding generations.
In addition, according to Chris Stringer from the Natural History Museum in London, people of African descent do not carry substantial amounts of Neanderthal DNA because their forebears were not part of the Out of Africa movement that took place before 40,000 years ago. On the other hand, Aboriginal Australians do carry Neanderthal/Denisovan ancestry so their ancestors must have reached Australia after Laschamp. A trace of an earlier disperal may survive in the genomes of some Papuans [New Guinea] whilst archaeological evidence from a rock shelter in Australia also indicates humans of some kind were present by around 65,000 years ago. The inference is they were Denisovans – but this has not been established as no fossil evidence exists. Were earlier dispersals replaced by newcomers or swamped by larger later waves of people, he asks, or did they become extinct. Megafauna became extinct in Australia during a mass die off event but not necessarily at the same time as Laschamp.
In a paper in Nature https://doi.org/10.1038/s41467-024-48395-x … evidence of humans in a cave on the island of Tmor show no sign of human activity prior to 44,000 years ago, we are told. Basically, the date of Laschamp once again, with dating methodology being updated by Bayesian means now creating holes in formerly accepted chronology. Is it possible humans did not need to inhabit caves prior to Laschamp as it is noticable that even the initial occupation is described as substantial. The geomagnetic phenomena associated with Laschamp involved heightened aurorae and perhaps an increase in cosmic radiation, leading to cave occurpation not only in SE Asia but in Europe too – at the same point in time. There is no reason why humans were not living on Timor prior to 44,000/42,000 years ago, we may note. It only looks like they had just arrived because they suddenly occupied a cave and left behind a lot of living refuse and evidence of camp fires etc.
This leads into another article on the same subject in https://phys.org/news/2024-07-adding-story-ancient-human-migration.html … where evidence of an ancient human migration and early maritime activities in Indonesia’s Tanimbar islands – dating back once again to 42,000 years ago. Tanimbar is located just off the Sahul continental shelf, which includes Australia and New Guinea, separating them from Timor. People, it is suggested, were moving around the coasts, exploring and settling down, or moving on to a more favourable location.