Summary of Tales of Human History Told by Neandertal and Denisovan DNA That Persist in Modern Humans

00:00:00 - 00:15:00

This video discusses the discovery that there was admixture between modern humans and Neanderthals and Denisovans, and how this affects our understanding of human evolution. It also discusses the presence of adaptive introgression, in which Neanderthal and Denisovan sequences were beneficial and rose to high frequency in the population.

• 00:00:00 The speaker discusses the history of human evolution and the debate over whether there was any admixture between modern humans and other groups of humans. They explain that, thanks to advances in DNA sequencing technology, we now know that there was admixture between modern humans and Neanderthals and Denisovans. Outside of Africa, individuals typically inherit 2% of their DNA from Neanderthals and Denisovans, while those in populations of Melanesian and Australian Aboriginal origin inherit a significantly different amount of Denisovan ancestry.
• 00:05:00 The video discusses how molecular excavations can be used to identify specific DNA sequences that were inherited from Neanderthal and Denisovan ancestors. It shows that, across all populations studied, about 41% of the Neanderthal genome and 10% of the Denisovan genome persists in modern individuals. The presenter tries to answer the question of whether the sequences inherited from Neanderthal and Denisovan ancestors had negative fitness consequences by looking at the distribution of these sequences across the genome. They find that there is a non-uniform distribution of these sequences, with some regions carrying a lot more than others.
• 00:10:00 The video discusses the significant depletion of Neanderthal and Denisovan sequence in the 10-megabase region on chromosome seven, which suggests that these genes were deleterious in modern humans and eliminated by natural selection. The talk also highlights the presence of adaptive introgression, in which Neanderthal and Denisovan sequences were beneficial and rose to high frequency in the population. This is interesting because modern humans are dispersing into new environments and picking up beneficial copies of genes from populations that have been there for hundreds of thousands of years.
• 00:15:00 This video discusses a study that found that a part of the signal of Neanderthal ancestry in Africa is due to an early out of Africa dispersal and gene flow from humans into Neanderthals. This adds a further twist to the complex pattern of admixture, gene flow, and arrows pointing in every direction that exists between Neanderthals, modern humans, and Denisovans.