At www.oxbowbooks.com/oxbow/blog/2021/06/23/archaeology-mystery-fate-of-nea… …. Oxbow talks to Dr April Nowell, author of 'Growing Up in the Ice Age' on the subject of the extinction of the Neanderthals. She is described as Palaeolithic archaeologist – specialising in the study of stone age societies and people. She is faced by a question – what happened to the Neanderthals 40,000 years ago? She begins by pointing out the physical and behavioural similarities between Neanderthals and modern humans, which makes their disappearance all the more puzzling. She runs through some of the various ideas on that such as modern humans committing genocide of the Neanderthals, on the basis they may have been seen as different, as well as climate change and competition from the newcomers. None of this is very convincing and she agrees. However, she has latched on to another theory. This is that Neanderthal populations were small and far flung, too widely dispersed. In other words 'in breeding' comes into play via limited local genetic variety. This led to even smaller numbers as offspring became genetically too close. Whether that would happen is just another theory and it would seem that mainstream really have no answer to the query. They simply dredge up another idea that is destined to be short-lived as it will not stand up to scrutiny. The problem is that without catastrophism as a possible factor they are simply casting round in circles. The date of 40,000 years ago is significant. It coincides with the Laschamp geomagnetic reversal and a mass die-off of animals – including mammoth and mastodon etc. The period, 40 to 30,000 years ago, coincided with the demise of large animals in Australia and in other parts of the world. It ushered in the Late Glacial Maximum. It also involved the disappearance of the Neanderthals and the appearance of modern humans – with a direct genetic link between the two. It has been said that as far as archaeology is concerned, at individual sites, there is always a distinction between Neanderthals and modern humans. They are never found at the same level. The Neanderthals are always found below strata with modern humans. There is a clear distinction.
She provides us with a research paper on the subject of a declining Neanderthal population – see https://doi.org/10.1371/journal.pone.0216742 … which is probably giving away the conclusion reached in her book, in case you were wondering whether or not to buy it.