We now understand that
the genus of primates became broadly distributed as early as almost two million
years ago. Thus there was always a
background of sister species for humanity to slowly evolve against and expand
into through either replacement or even hybridization.
I notice that the dates
are falling rapidly now as if it appears that researchers are becoming more aggressive
and looking much deeper. After all the
only way to disprove an earlier date is to do just that. Thus we are getting good news and filling in
many obvious holes that conjecture easily sees.
The interesting
question now is why certain creaturs traveled well while others did not.
Out of Africa: 1.8
M-year-old skull shows early human ancestors evolving and on the move
DMANISI,
Georgia - The discovery of a 1.8-million-year-old skull of a human ancestor
buried under a medieval Georgian village provides a vivid picture of early
evolution and indicates our family tree may have fewer branches than some
believe, scientists say.
The
fossil is the most complete pre-human skull uncovered. With other partial
remains previously found at the rural site, it gives researchers the earliest
evidence of human ancestors moving out of Africa and spreading north to the
rest of the world, according to a study published Thursday in the journal
Science.
The
skull and other remains offer a glimpse of a population of pre-humans of
various sizes living at the same time — something that scientists had not seen
before for such an ancient era. This diversity bolsters one of two competing
theories about the way our early ancestors evolved, spreading out more like a
tree than a bush.
Nearly
all of the previous pre-human discoveries have been fragmented bones, scattered
over time and locations — like a smattering of random tweets of our
evolutionary history. The findings at Dmanisi are more complete, weaving more
of a short story. Before the site was found, the movement from Africa was put
at about 1 million years ago.
When
examined with the earlier Georgian finds, the skull "shows that this
special immigration out of Africa happened much earlier than we thought and a
much more primitive group did it," said study lead author David
Lordkipanidze, director of the Georgia National Museum. "This is important
to understanding human evolution."
For
years, some scientists have said humans evolved from only one or two species,
much like a tree branches out from a trunk, while others say the process was
more like a bush with several offshoots that went nowhere.
Even
bush-favouring scientists say these findings show one single species nearly 2
million years ago at the former Soviet republic site. But they disagree that
the same conclusion can be said for bones found elsewhere, such as Africa.
However, Lordkipanidze and colleagues point out that the skulls found in
Georgia are different sizes but are considered to be the same species. So, they
reason, it's likely the various skulls found in different places and times in
Africa may not be different species, but variations in one species.
To
see how a species can vary, just look in the mirror, they said.
"Danny
DeVito, Michael Jordan and Shaquille O'Neal are the same species,"
Lordkipanidze said.
The
adult male skull found wasn't from our species, Homo sapiens. It was from an
ancestral species — in the same genus or class called Homo — that led to modern
humans. Scientists say the Dmanisi population is likely an early part of our
long-lived primary ancestral species, Homo erectus.
Tim
White of the University of California, Berkeley, wasn't part of the study but
praised it as "the first good evidence of what these expanding hominids
looked like and what they were doing."
Fred
Spoor at the Max Planck Institute in Germany, a competitor and proponent of a
busy family tree with many species disagreed with the study's overall
conclusion, but he lauded the Georgia skull discovery as critical and even
beautiful.
"It
really shows the process of evolution in action," he said.
Spoor
said it seems to have captured a crucial point in the evolutionary process
where our ancestors transitioned from Homo habilis to Homo erectus — although
the study authors said that depiction is going a bit too far.
The
researchers found the first part of the skull, a large jaw, below a medieval
fortress in 2000. Five years later — on Lordkipanidze's 42nd birthday — they
unearthed the well-preserved skull, gingerly extracted it, putting it into a
cloth-lined case and popped champagne. It matched the jaw perfectly. They were
probably separated when our ancestor lost a fight with a hungry carnivore,
which pulled apart his skull and jaw bones, Lordkipanidze said.
The
skull was from an adult male just shy of 5 feet (1.5 metres) with a massive jaw
and big teeth, but a small brain, implying limited thinking capability, said
study co-author Marcia Ponce de Leon of the University of Zurich. It also seems
to be the point where legs are getting longer, for walking upright, and smaller
hips, she said.
"This
is a strange combination of features that we didn't know before in early
Homo," Ponce de Leon said.
___
Borenstein
reported from Washington.
___
Seth
Borenstein can be followed at http://twitter.com/borenbears
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