Brachiation

  Brachiation is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.

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Brachiators

The only true brachiators are the lesser apes (gibbons and siamangs). A gibbon can brachiate at speeds as high as 35 mph and can travel as far as 20 feet with each swing. Spider monkeys and orangutans are considered semibrachiators.

Brachiation-aiding traits

Some of the traits that allow gibbons, siamangs, and other primates to brachiate include the following: short fingernails instead of claws, inward-closing, hook-like fingers, opposable thumbs, long forelimbs, and freely rotating shoulder joints.

Brachiation and humans

Modern humans retain many physical characteristics that suggest a protobrachiator ancestor, including flexible shoulder joints and fingers well-suited for grasping. In apes, these characteristics were adaptations for brachiation. Although humans do not brachiate, our anatomy suggests that brachiation may be a preadaptation to bipedalism.

References

1. Rice, Patricia C.; Norah Moloney (2005). Biological Anthropology and Prehistory: Exploring our Human Ancestory. Pearson Education, Inc., pp. 178-179, 192. ISBN 0205381960
2. Brittanica.com
3. Dictionary.com
4. MSN Encarta