Re: Beyond the Savanna Mentality
- From: Rich Travsky <" traRvEsky"@hotmMOVEail.com>
- Date: Sun, 02 Oct 2005 22:30:32 -0600
Marc Verhaegen wrote:
>
> http://www.discover.com/issues/oct-05/features/human-origins/
>
> Thanks, DD!
Thanks to DD for noting, and you're welcome for the link.
> 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
we're finding an association of early hominid fossils with faunas more
characteristic of woodlands, of more closed habitats.
Nothing littoral there.
> 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.
.
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