DMANISI, Georgia (AP) — 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-favoring 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 meters) 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.