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.
'The findings are more complete'
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
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
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.
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
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.
What the researchers found
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.