Advantaged By a Single Base?

Modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) both originated in Africa. The latter migrated early to the North and became established in Europe and Asia, leaving their 'cousins' in Africa. Neanderthals presumably would have become adapted to their new locations. A mass migration of modern humans out of Africa occurred around, 60,000 years ago. This brought them into contact with Neanderthals. The two species (or more properly sub-species?) interbred. Now, modern humans have 1-4% Neanderthal DNA. Circa 30,000 years ago, Homo neanderthalensis disappeared as a separate species. They must have been out-competed by Homo sapiens. The question is why? Homo neanderthalensis would have had longer to adapt to conditions in Europe and elsewhere. It's been long-suggested that modern humans must have been more intelligent. There now appears to been some actual evidence, to support this supposition (https://www.theguardian.com/science/2022/sep/08/study-reveals-striking-differences-in-brains-of-modern-humans-and-neanderthals). TkTLi is a gene involved in neuronal production in the developing brain. The Homo sapiens and Homo neanderthalensis versions differ only by a single DNA base (as Sickle cell anaemia differs from normal haemaglobin). Studies inserting these genes into mice and ferrets, showed differences in neuronal development in key areas. Later investigations inserted the genes into 'mini brain' organoids, laboratory-grown from human stem cells (special cells able to differentiate into different cell types). The Neanderthal version of the gene resulted in slower neurone creation in the brain 'cortex'. Faster neurone creation in the developing brains of Homo sapiens, might well have resulted in superior cognition (thought processing), enabling them to out-compete Neanderthals.