Recently I've had the bug to go and research human evolution. Kinda
cool I know, but slightly off topic for my normal blog. Still, the urge
is strong, and I found myself spending hours on the net looking up
resources and papers. I think the local library is about to cut me off,
but besides that, its been fun and oddly thrilling. That which holds my
attention the most are our cousin species H. Neanderthal and H.
Denisovan.
Let's cover things I already know...
First,
Our current human species, H. Sapien (modern humans) is the first human
species to not have a living cousin species. This was not always the
case though. When we first stepped out of Africa some 100,000 years ago,
we encountered the Neanderthals. Neanderthal already had a pretty
strong foothold in Europe, as they are decedent from H. Erectus who
migrated to Eurasia about 900,000 years before that.
Now new things...
When I was in school, we were
taught that at some point, in some way, Humans replaced Neanderthals.
We weren't sure if it was by out breeding them or by killing them, but
because we knew the two were separate species it could not have been by
interbreeding. Which was a major crush to me, because I really like the
idea of interbreeding. However, there was no evidence at the time to
support that.
Then came the report of The Child of Lapedo,
a child that was found to have physical traits of both Neanderthals and
Modern Humans. This was huge! But aside from using physical traits of
the bones, there was no way to confirm 100% that the boy was a hybrid.
Even if he had been, he had died at the age of 4, hardly old enough to
reproduce.
Then came the most wonderful Neanderthal Genome Project
lead by Svante Paabo, and not too shortly after that the discovery that
modern humans contain Neanderthal DNA. About 2.5% of it in
non-Africans. This made my day, really it did. I'm always very excited
when we find that Neanderthals are more like us than we thought. The
excitement didn't end there however.
In 2008
a finger bone and tooth were found in Denisova Cave in southern
Siberia, Russia, the tooth showing no signs of being human. Paabo and
his team were called in to examine the remains and found that they were
genetically similar to Neanderthals, but not exactly. Further, they were
able to find a group of modern humans who were still carrying Denisovan
DNA...modern Papa New Guineans.
According to an article on NPR by Ursula Goodenough the story might have looked very much like this:
Sometime
after Ancestor X diverged and became either H. Sapien or H. Erectus,
Erectus migrated out of Africa and into Eurasia about a million yeas
ago. Before going extinct about 500,000 years ago, Erectus itself
diverged into two distinct lines, H. Neanderthal and H. Devisovan. These
two populations managed to stay separate long enough for spieciation to
occur. Then modern humans migrated out of Africa about 200,000 years
ago and interbred with Neanderthal. This created a group of humans who
were 2.5% Neanderthal and 97.5% Sapien.
And Then...
A
group of these humans migrated west and encountered and interbred with
the Denisovans creating a third human grouping that is 92.5% Sapien,
2.5% Neanderthal and 5% Denisovan.
This intermingling
of the different hominid species does raise some very important
questions, one being the definition of 'species'. Traditionally, two
different species can not produce viable offspring. Either they can't
produce offspring at all, or the offspring is infertile. Think Mules,
the infertile hybrid offspring of Horses and Donkeys. However, if modern
humans still have trace amounts of Neanderthal and Denisovan DNA, then
hybrid individuals were able to continue breading.
This
is a major topic that will continue to develop over the coming years as
more research is done. Until then I shall bite my nails in
anticipation.
Resources:
EurekAlert!
2010 Genome of extinct Siberian cave-dweller linked to modern-day humans
Public release date: 22-Dec-2010
Accessed 2/7/2011
Goodenough, Ursula
2011 Leaky Replacement: Human, Neanderthal And Denisovan Blends
NPR Website, www.NPR.org
Accessed 2/7/2011
Trinkaus, Erik et. al.
PNAS website, www.pnas.or
Accessed 2/7/2011
