So, unless some weird evolutionary reversals have taken place, A is the most basal clade in the human Y-chromosome phylogeny.Chimp and human Y chromosomes are very divergent (see <a href="http://www.nature.com/nature/journal/v463/n7280/full/nature08700.html),">http://www.nature.com/nature/journal/v463/n7280/full/nature08700.html),</a> and this fact was ascertained after the human Y-DNA tree had been built.