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blivet radio
The Radio weblog of Hal Rager
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Thursday, May 9, 2002 |
"In response to periods of cooling and drying, which thinned out dense forests and produced "mosaics" of forests, woodlands and grasslands, it seems likely that "some apes maintained a forest-oriented adaptation, while others may have begun to exploit forest margins and grassy woodlands," said paleoanthropologist Brian Richmond, lead author in the new study. The process of increasing commitment to bipediality probably involved "an extended and complex opening of habitats, rather than a single, abrupt transition from dense forest to open savanna," he said.
Richmond, from the University of Illinois at Urbana-Champaign, with paleoanthropologists David Begun from the University of Toronto and David Strait from the New York College of Osteopathic Medicine, describe their findings, which involved a comprehensive review and analysis of the five leading hypotheses on the origin of bipedalism, in a recent issue of the Yearbook of Physical Anthropology. Other hypotheses that remain viable, according to the team: "freeing" the hands for carrying or for some kind of tool use, and an increased emphasis on foraging from branches of small fruit trees, which is the context in which modern chimpanzees spend the most time on two legs.
For their study, the researchers combined data from biomechanics -- movement, posture and stesses in bones and joints -- and from bone growth and development. They found that our prehuman ancestors had terrestrial features in the hands and feet, climbing features throughout the skeleton, and knuckle-walking features in the wrist and hand; that finger bone curvature is responsive to changes in arboreal activity during growth, lending support to the hypothesis that many early hominid species, although bipedal, still climbed trees. Evidence from the wrist joint "suggests that the earliest humans evolved bipedalism from an ancestor adapted for knuckle-walking on the ground and climbing in trees."
The YPA article, according to Richmond, is "the first attempt in decades to bring together all of the available evidence for the argument that the earliest human biped evolved from ancestors that both knuckle-walked and climbed trees, rather than from ancestors living exclusively in trees and 'coming down from the trees,' or walking on the ground in ways similar to modern baboons."" [Science Daily]
8:33:34 AM 
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"Most theories on the origin of cellular life presume that the first step was the formation of a spherical membrane called a vesicle that could enclose self-replicating chemical chains - the ancestors of modern DNA. The idea is that the ingredients for simple membranes were all present on the early Earth, and at some point formed vesicles spontaneously in water.
It seemed most likely that this took place in the sea rather than freshwater, largely because of the sheer size of the oceans. With their unique chemistry, deep-sea thermal vents and tidal pools are generally believed to be the most likely sites.
Now research by graduate student Charles Apel of the University of California, Santa Cruz, suggests that this is wrong. Apel and his colleagues were able to create stable vesicles using freshwater solutions of ingredients found on the early Earth, but not salty solutions, they will report in a future issue of Astrobiology.
"When sodium chloride or ions of magnesium or calcium were added the membranes fell apart," Apel says. This happened in water that was less salty than the oceans are today.
Geologist L. Paul Knauth of Arizona State University points out that Earth's early oceans were 1.5 to 2 times as salty as they are today, making it even more unlikely that viable cells could have arisen there. Giant salt deposits called evaporites that formed on the continents have actually made the seas less salty over time."
[New Scientist]
8:25:43 AM
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