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RE: [palanthsci] Human Ancestors Walked Upright, Study Claims

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  • Dave Timpe
    Another case of a headline writer miscasting the story, which isn t all that bad, as it turns out. Obviously, for anyone who s been following events even
    Message 1 of 2 , Oct 10, 2007

      Another case of a headline writer miscasting the story, which isn’t all that bad, as it turns out.  Obviously, for anyone who’s been following events even distantly, it’s no news that “human ancestors” walked upright.  The news is which ancestors, when.  I leave it to others to decide whether Filler’s central claim about the horizontal septum has any validity.  Still, the idea that great apes have a preadaptation to bipedalism owing to their vertical posture in trees has also been kicking around for awhile.

       

      Dave

       


      From: palanthsci@yahoogroups.com [mailto: palanthsci@yahoogroups.com ] On Behalf Of maria guzman
      Sent: Wednesday, October 10, 2007 5:04 PM
      To: palanthsci@yahoogroups.com
      Subject: [palanthsci] Human Ancestors Walked Upright, Study Claims

       

      FYI. Maria

       

       

       

      Human Ancestors Walked Upright, Study Claims

      By Charles Q. Choi, Special to LiveScience

      posted: 09 October 2007 09:57 pm ET

       

      The ancestors of humanity are often depicted as knuckle-draggers, making

      humans seem unusual in our family tree as "upright apes."

       

      Controversial research now suggests the ancestors of humans and the other

      great apes might have actually walked upright too, making knuckle-walking

      chimpanzees and gorillas the exceptions and not the rule.

       

      In other words, "the other great apes we see now, such as chimps or gorillas

      or orangutans, might have descended from human-like ancestors," researcher

      Aaron Filler, a Harvard-trained evolutionary biologist and medical director

      at Cedars-Sinai Institute for Spinal Disorders in Los Angeles , told

      LiveScience.

       

      Filler analyzed how the spine was assembled in more than 250 living and

      extinct mammalian species, with some bones dating up to 220 million years

      old.

       

      He discovered a series of changes that suggest walking upright-and not with

      our knuckles-might actually have been the norm for the ancestors of today's

      great apes.

       

      In most creatures with a backbone, the body is separated roughly in half by

      a tissue structure that runs in front of the spinal canal. This "horizontal

      septum" divides the body into a dorsal part (corresponding to the back side

      of humans), and a ventral part (or the front half).

       

      A strange birth defect in what may have been the first direct human ancestor

      led this septum to cross behind the spinal cord in the lumbar or lower back

      region-an odd configuration more typical of invertebrates. This would have

      made horizontal stances inefficient.

       

      "Any mammal with this set of changes would only be comfortable standing

      upright," Filler said. "I would envision this malformed young

      'hominiform' -the first true ancestral human-as standing upright from a young

      age," he added, while the rest of the mutant's family and species continued

      to walk around "on all fours."

       

      This change to an upright posture could have occurred "very abruptly, with

      just a few shifts in 'homeotic' genes, or ones responsible for how the body

      plan is laid out," Filler said.

       

      The earliest known bipedal apes-those walking on two legs-were thought to

      date back as far as some 6 million years or so. Now Filler's new findings

      suggest the earliest upright ape known so far was the extinct hominoid,

      Morotopithecus bishopi, which lived in Uganda more than 21 million years

      ago.

       

      "Humanity can be redefined as having its origin with Morotopithecus, " Filler

      said. He detailed his findings online Oct. 10 in the journal PLoS ONE.

       

      This research pushes back the date for the origins of bipedalism roughly 15

      million years, to before the last common ancestor of humans, chimps,

      gorillas and orangutans, as well as lesser apes such as gibbons. The results

      match up with recent findings that suggest upright walking might have

      started before humanity's ancestors even left the trees.

       

      "If you look at baby siamangs, which are a kind of gibbon, you'll see them

      walk bipedally on their own," Filler said. "It's just their natural way of

      walking. They never knuckle walk."

       

      If bipedalism did evolve 21 million years ago, it more likely evolved to

      walk in trees than on the ground, said University of Chicago evolutionary

      anthropologist Russell Tuttle. "Twenty-one million years ago, there were a

      lot of trees around," he said.

       

      Besides Morotopithecus, fossil vertebrae suggest three other upright ape

      species precede the 6 million year mark, Filler added.

       

      "So you have this fossil evidence for bipedalism, and you have apes such as

      gibbons," he said. "Perhaps humans represent the primitive condition, and

      knuckle walkers such as chimps and gorillas are modified."

       

      The ancestors of chimps and gorillas might have evolved knuckle walking as a

      speedier mode of travel, Filler suggested. If bipedalism did come first,

      that means gorillas and chimpanzees might have evolved knuckle walking

      independent of each other. Future analysis of the genes of those apes could

      show they came across knuckle walking in different ways, supporting Filler's

      ideas.

       

      "I am getting the feeling that a revolution in our thinking about the

      origins of bipedality is now under way," said evolutionary anthropologist

      Robin Crompton at the University of Liverpool in England .

       

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