Re: Beyond the Savanna Mentality

http://www.discover.com/issues/oct-05/features/human-origins/

Thanks, DD!

Finally they agree that the hominid LCA was partly bipedal (short-legged) &
that they did not live in savannas - things we "predicted" long ago - but
most PAs have still a long way to go before they understand something on
human & ape evoution.

--Marc
_______

Human Origins
Digital Ancestors Walk Again
Commonplace hospital gear opens up a new way of reconstructing forerunners
of Homo sapiens
Carl Zimmer
DISCOVER Vol.26 No.10 Oct.2005 Anthropology

In the past, most of the big news about human evolution came from remote dig
sites in places like Africa or Indonesia. In the future, the big news will
come from familiar sites closer to home: hospitals. That's because hospitals
are equipped with powerful new scanning machines primarily used to identify
tumors, ballooning blood vessels, bone fractures, and a wide range of
disorders in people. Those same scanners also make it possible for
paleoanthropologists to look inside the fossils of ancient hominids and see
things that until now have been shrouded in mystery.

Take brains, for example. The evolution of the human brain is one of the
most important questions in the story of our origins. But when our ancestors
died, their brains quickly rotted away. Fossilized skulls offer the only
clues. Until recently, if a team of researchers found an intact braincase,
they were limited in what they could learn unless they cut the fossil open.
Because hominid skulls are rare, few would dare take such a radical step.

Now paleoanthropologists can put a hominid skull in a computed-tomography,
or CT, scanner and create a virtual skull that they can split apart any way
they want. If they remove that digital skull altogether, they leave behind
the outlines of a virtual brain. In 2005 a virtual brain of the one known
skull of Homo floresiensis-the three-foot-tall hominid discovered on the
Indonesian island of Flores-provided evidence in the ongoing debate about
whether the creature represents a separate species or was a human pygmy with
a birth defect. The size and shape of the virtual brain lends credence to
the separate species theory. Moreover, the brain was not just a simpler
version of a human brain. Some regions were smaller than ours, but others
were unusually large for such a small hominid, hinting that Homo
floresiensis might have been capable of abstract thought and could make
complicated plans.

Most hominid fossils are in much worse shape than the skull of Homo
floresiensis. Over thousands of years, they have disintegrated.
Reconstructing a skull from bone chips used to be like assembling a
three-dimensional puzzle with most of the pieces missing. Debates flare up
over reconstructions. Was this hominid tall or short? Was that fossil a
single individual, or a mélange of several? When they try new
reconstructions, paleoanthropologists often wind up damaging the fossils as
they cut through the glue and varnish that held pieces together. And when
fossils are particularly smashed up, paleoanthropologists simply don't dare
reconstruct them.

CT scans make it much easier to put these puzzles back together. Researchers
can create virtual bone fragments and then use sophisticated mathematical
software to find the best way to assemble them. In some cases, they can make
the scans without even removing the fossils from the rock that encases them.
This new method has already changed the way scientists think about
Neanderthals. A Swiss research team has produced a virtual series of young
Neanderthal skulls and compared their development with that of modern human
children. It turns out that Neanderthal children are as different from
modern humans as adult Neanderthals are-which suggests that Neanderthals did
belong to a separate species and did not give rise to living Europeans.

As the use of CT scans expands, paleoanthropologists are developing new
avenues for uncovering clues to our past. They are discovering signs of
healed wounds, of toothless old hominids who must have been cared for by
others. Some researchers are even producing full-length virtual skeletons to
which they can attach virtual muscles and make the ancient hominids walk
again. Most significantly, CT scans can liberate hominid fossils from museum
drawers. Once a research team makes a scan, they can post the data on a Web
site for other researchers to analyze, bringing a precious hominid fossil to
new sets of eyes and new sets of questions.

SKULL REVELATIONS
One of the biggest surprises in the attempt to figure out human evolution
comes from a crushed skull dug up in the Sahara in 2001. It belongs to a
species of prehumans called Sahelanthropus tchadensis, which lived between 6
million and 7 million years ago. Although the find was remarkable, it wasn't
until this year that a team led by French paleoanthropologist Michel Brunet
used CT scans to create a virtual model of the skull, revealing precise
measurements of the size of the brain cavity and information about the angle
at which the spinal cord exits the brain. The results showed that even
though this hominid's brain was no larger than a chimpanzee's, it most
likely walked upright like modern humans. Bipedalism, one of the basic
markers of humans, apparently developed long before other traits, such as
stone-tool making.

ANGLE OF ATTACK:The chimpanzee (PAN TROGLODYTES) walks on all fours, a fact
that is reflected in the anatomy of its head. The spinal cord enters high on
the skull through a hole called the foramen magnum. A line drawn from this
opening forms an acute angle with a line running through the eye socket
(known as the orbital plane). In SAHELANTHROPUS TCHADENSIS and HOMO SAPIENS,
the spinal cord enters the brain on a nearly vertical line, creating a much
larger angle. The larger angle corresponds to a head held in an upright
position and may show that Sahelanthropus walked on two legs.

DIALOGUE

Beyond the Savanna Mentality

TIM WHITE of the University of California at Berkeley has been at the
frontier of paleoanthropology since the 1970s, when he helped discover
fossils of Australopithecus afarensis, a species that includes the famous
"Lucy" skeleton. Since then he has focused his efforts on a small region of
central Ethiopia, where he discovered a variety of fossils, from
5.5-million-year-old hominids to some of the earliest members of our own
species, dating back 160,000 years.

How do you manage to find so much history in such a small region?
W: The reason that we're able to do it is that it's just a geological
nightmare. You have a patchwork quilt of different aged sediments on the
surface. You can step across a fault and step back 2 million years. It
allows you to look through many different windows in one small area.

How is our view of early hominid evolution changing?
W: We had become so used to finding hominids in open country that there was
an expectation that all hominid origins could be related to a shift from
forest to savanna. You could characterize it as the savanna mentality. Now
we're finding an association of early hominid fossils with faunas more
characteristic of woodlands, of more closed habitats. We've also learned
that the idea that the last common ancestor of hominids was like a
chimpanzee is just wrong. The more closely we approach that last common
ancestor with real fossils, we're learning that its browridge is shaped
differently from any chimpanzee's, and its canine teeth are much smaller.
Chimpanzee incisor teeth are very broad, and they use them for eating
fruits. We don't see that in any of the oldest hominids. This is saying that
chimpanzees evolved that specialization after the split with our ancestors.
We're able to put together a picture of the earliest hominids quite
different from a projection one might have made from Lucy-a picture that
allows us to see ourselves as a specialized primate.

What technology advances are changing the way you study evolution?
W: The global positioning satellite system. With GPS, we no longer have to
worry about the position of a fossil. Some of the biggest blunders in the
history of paleoanthropology were made by people who lost the place where a
fossil came from. There's no excuse for that anymore. The other big advance
is in geochemical dating. Consider an analogous situation. Let's say you're
interested in Columbus's exploration of the Caribbean, and you go into the
library and someone has removed all the dates from the documents. We face a
similar challenge. It is the order of the succession that is really
important-particularly when you're trying to understand evolution.

What big developments do you anticipate?
W: The major progress will come from knowledge about how anatomy is formed.
It's the integration of data from fossils and developmental biology. For
example, when you look at the length of your thighbone, you might ask: Why
is the human thighbone so much longer than the chimpanzee thighbone? We can
answer that question in a very simplistic way right now. The growth plates
on the end of the chimpanzee femur fuse earlier. But we're at a stage where
we can ask new questions: What signaling between cells is leading to that?
How easy is it for the femur to be extended? And then we can apply those
insights to the fossil record. When did the femur lengthen? Another great
example is the hand. In a chimpanzee or gorilla hand the metacarpals [palm
bones] are really long. In humans they're quite short. Again, how that
happens genetically is a question that can be addressed in the laboratory.
Then we can take that knowledge and play it against the fossil record. Lucy'
s hand had a relatively short thumb. When was it in human evolution that the
thumb elongated? How do the genetic controls over thumb length differ from
the controls over the other digits? It's that synthesis that I see coming in
20 years. But right now it's way early in the game.

Attributing a particular gene to the expansion of the brain is just kind of
silly. Downstream, though, it's going to be fascinating. Of course, no
amount of work on the human and chimpanzee genome could have ever resulted
in the knowledge about a 3.2-million-year-old hominid ancestor in terms of
its anatomy, its ecology, or its behavior. You don't discover a Lucy in the
molecular laboratory.


.

Relevant Pages

  • Re: Beyond the Savanna Mentality
    ... > Finally they agree that the hominid LCA was partly bipedal & ... > paleoanthropologists to look inside the fossils of ancient hominids and see ... The evolution of the human brain is one of the ... scanner and create a virtual skull that they can split apart any way ...
    (sci.anthropology.paleo)
  • Re: Beyond the Savanna Mentality
    ... > we're finding an association of early hominid fossils with faunas more ... The evolution of the human brain is one of the ... scanner and create a virtual skull that they can split apart any ...
    (sci.anthropology.paleo)
  • Re: Beyond the Savanna Mentality
    ... >> we're finding an association of early hominid fossils with faunas more ... scanner and create a virtual skull that they can split apart any ... The size and shape of the virtual brain lends credence ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... > presume) acidic and therefore not conducive to producing fossils. ... > we have a sizeable number of hominid fossils, and no ancestral chimp, ... > chimp or bonobo or gorilla is identified, we will have a better idea ...
    (sci.anthropology.paleo)
  • Toumai Reconstruction Seems To Confirm Placement In Hominid Lineage
    ... The virtual reconstruction of a skull unearthed at the base of the Saharan ... tchadensis is the oldest known member of the hominid lineage, ... backwards, explains Dan Lieberman, a palaeoanthropologist at Harvard ...
    (sci.anthropology.paleo)