Tonyk
Thu, Jul-18-02, 01:17
Found this at
http://www.sciencedaily.com/releases/2002/05/020509074029.htm
CHAMPAIGN, Ill. -- During the past 100 years, scientists have
tossed around a great many hypotheses about the evolutionary
route to bipedalism, and what inspired our prehuman ancestors
to stand up straight and amble off on two feet. Now, after an
extensive study of evolutionary, anatomical and fossil
evidence, a team of paleoanthropologists has narrowed down the
number of tenable hypotheses to explain the origin of
bipedalism and our prehuman ancestors' method of navigating
their world before they began walking upright.
The hypothesis they found the most support for regarding the
origin of bipedalism is the one that argues our ancestors
began walking upright largely in response to environmental
changes -- in particular, to the growing incidence of open
spaces and the way that changed the distribution of food.
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."
Editor's Note: The original news release can be found at
http://www.news.uiuc.edu/scitips/02/05bipedal.html TonyK
http://www.sciencedaily.com/releases/2002/05/020509074029.htm
CHAMPAIGN, Ill. -- During the past 100 years, scientists have
tossed around a great many hypotheses about the evolutionary
route to bipedalism, and what inspired our prehuman ancestors
to stand up straight and amble off on two feet. Now, after an
extensive study of evolutionary, anatomical and fossil
evidence, a team of paleoanthropologists has narrowed down the
number of tenable hypotheses to explain the origin of
bipedalism and our prehuman ancestors' method of navigating
their world before they began walking upright.
The hypothesis they found the most support for regarding the
origin of bipedalism is the one that argues our ancestors
began walking upright largely in response to environmental
changes -- in particular, to the growing incidence of open
spaces and the way that changed the distribution of food.
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."
Editor's Note: The original news release can be found at
http://www.news.uiuc.edu/scitips/02/05bipedal.html TonyK