There is a general scientific consensus that homo sapiens interbred with Neanderthals and that the Eurasians retained 1-2% of the Neanderthal genes. The East Asians have about 20% more Neanderthal genes than their European brethren which suggests a longer duration of their intermixing with Neanderthals.
There are many hypotheses about the extinction of Neanderthals which include conflict with early modern humans who may have killed the Neanderthal groups, or may have been infected with diseases by coming in contact with humans. One important hypothesis is about the climate change and volcanic eruptions which may have eliminated Neanderthals. Climate analysis indicate that the regions had cold and dry climate about 44000 years ago which lasted some 1000 years. This was followed by another cold and dry period around 40800 years ago and lasted about 600 years. During these periods the temperatures were sub-zero throughout that time, which may have been the reason for the extinction of Neanderthals, though they may have phased out slowly.
Genomic analysis of modern human bones dating around 40000 years before present indicate no Neanderthal genes or gene deserts which is a proof that the gene flow occurred later on. Analysis of modern humans of 30000 years old shows a high frequency of Neanderthal genes and gene deserts which indicated the intermixing between the two groups during this time frame. Gene deserts are those regions of the genome which are non-coding for proteins but may have profound regulatory functions. The Neanderthal genes present among humans are related to skin pigmentation, metabolism, immune function and one gene variant provides protection against COVID-19. These genes incorporated among some human groups before 30000 years ago may have been beneficial to humans in those harsh climatic conditions which remained embedded in their genomes.
Professor S. P. Singh, Ph.D.
Editor-in-Chief, Human Biology Review
Former Dean, Faculty of Life Sciences,
Punjabi University, Patiala, India