Washington, Sep 6 - Modern
humans may have interbred with a now extinct lineage of humanity before leaving
Africa 65,000 yeas ago, according to a new
research.
DNA
studies have already proved that ancestors of modern humans got intimate with
Neanderthals in Europe and another Asian
relative called the Denisovans.
Now,
researchers found that our earliest ancestors had sex with a hitherto unknown
human lineage and it may date to beyond the point when anatomically modern
humans first emerged 200,000 years ago.
The
species who may have contributed to the modern gene pool include Homo erectus,
the upright walking man, and the Òtool-using manÓ Homo habilis, the researchers
said.
Lead
researcher Michael Hammer, from the University
of Arizona, said it looks
like our lineage has always exchanged genes with their more morphologically
diverged neighbours.
ÒWe think there were probably thousands of
interbreeding events. It happened relatively extensively and regularly,Ó Hammer
was quoted as saying by LiveScience.
For their research, published in the journal
Proceedings of the National Academy of Sciences, Hammer and his colleagues
sequenced about 60 regions of the human genome that apparently have no
function.
These genes are less subject than functional
DNA to change as a result of recent evolutionary pressures driving the survival
of the fittest; in such a way, they can give a clearer view of how populations
might have mixed or not in the past.
The team focused on three
populations that presented a good sample of the geographic and cultural
diversity of sub-Saharan Africa -- Mandenka farmers in western Africa, Biaka
Pygmies in westcentral Africa, and San Bushmen of southern Africa
-- looking for unusual patterns that suggested ancient interbreeding with other
lineages.
They
discovered strong evidence of genetic mixing in the Biaka and San. By comparing
these sets of genes with those from comparable modern human ones, they
estimated the unusual genes may have come from a lineage that first diverged
from the ancestors of modern humans about 700,000 years ago.
For context, the Neanderthal lineage diverged
from ours within the past 500,000 years, while the first signs of anatomically
modern human features appeared only about 200,000 years ago.
ÒThe populations that interbred in Africa were
on a similar scale of divergence as the expanding modern population and
Neanderthals were outside of Africa,Ó Hammer
said.
ÒThey were similar enough
biologically so that they were able to produce fertile offspring, thus allowing
genes to flow from one population to the other.Ó The length of exotic
haplotypes (a set of DNA sequences) from this extinct lineage suggests
interbreeding might still have occurred until as recently as 35,000 years ago,
he added.
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