Question

3- Prüfer et al. showed that a phylogenetic tree built with autosomal transversion substitutions resulted in the clustering of Denisovans with Neanderthals (with 100% bootstrap support). Modern humans became the out-group in this phylogenetic tree, but still the results showed that all modern humans clustered with each other (also with 100% bootstrap support, see figure 2b). Discuss the significance of these results, in terms of the possible common origin of all modern humans, as well as the possible common origin of Denisovans and Neanderthals from a single migrating population (if so, where would that population have been, and when?). Is 100% bootstrap support sufficient to establish these conclusions? Why (or why not)?

Prüfer, K. et al. (2014) The complete genome sequence of a Neanderthal from the Altai Mountains. Nature 505, 43-49.

Answer 1

There is a possible common origin of all modern humans as well as possible common origin of the Denisovans and Neaderthals from a single migrating population. This was seen by sequencing genome of high quality of Neaderthal woman. On analysis of the sequence and the relationship, it is found that around 25 present day human genomes that there are number of gene flow events which occurred in the Neaderthals, Denisovans and the early modern humans. The connection of the modern humans and the Denisovans and Neanderthals is mostly due to possible gene flow that possibly might have originated from an unknown archaic group. The bootstrap values are used and shown for branches that is supported by less than 100% of the overall 1000 bootstrap replicates. Hence 100% bootstrap is not sufficient to establish the conclusion that the similarity might be due to the gene flow.