Abstract
Recent studies have shown that hybridization between modern and archaic
humans was commonplace in the history of our species. After admixture, some
individuals with admixed autosomes carried the modern Homo Sapiens uniparental
DNAs, while the rest carried the archaic versions. Coevolution of admixed
autosomes and uniparental DNAs is expected to cause some of the sites in modern
uniparental DNAs to revert back to archaic alleles, while the opposite process
would occur (from archaic to modern) in some of the sites in archaic
uniparental DNAs. This type of coevolution is one of the elements that
differentiate the two different models of the Y phylogenetic tree of modern
humans, rooting it either in Africa or East Asia. The expected reversion to
archaic alleles is assumed to occur and is easily traceable in the Asia model,
but is absent in the Africa model due to its infinite site assumption, which
also precludes the independent or convergent mutation to modern alleles in
archaic uniparental DNAs since mutations are assumed to occur randomly across a
neutral genome, and convergent evolution is assumed not to occur. Here, we
examined newly published high coverage Y chromosome sequencing data of two
Denisovan and two Neanderthal samples to determine whether they carry
modern-Homo Sapiens alleles in sites where they are not supposed to according
to the Africa model. The results showed that a significant fraction of the
sites that, according to the Asia model, should differentiate the original
modern Y from the original archaic Y carried modern alleles in the archaic Y
samples here. Some of these modern alleles were shared among all archaic humans
while others could differentiate Denisovans from Neanderthals. The observation
is best accounted for by coevolution of archaic Y and admixed modern autosomes,
and hence supports the Asia model, since it takes such coevolution into
account.