Why do paleoanthropologists consider bipedalism to be an Obligate anatomical adaptation in the human lineage?

Question

Why do paleoanthropologists consider bipedalism to be an Obligate anatomical adaptation in the human lineage?

Answer 1

Since bipedalism developed in hominids prior to encephalization, selection was on pelvic locomotor anatomy. There is a functional conflict between demands of bipedalism and the necessity of a birth canal large enough to accommodate the infant's shoulders. A substantial increase in brain size could be accommodated by the birth canal, and further slight increases in neonatal brain size could be accommodated by reducing the face and presenting the head during birth in a different manner to the birth canal. A reduction in muzzle length could be a compromise to the selective pressures associated with encephalization and bipedalism. We now have a protohominid with bipedalism, slight encephalization, and possibly a reduced muzzle that occupies a niche somewhere between the chimpanzee and baboon. That is, it uses the ground like a baboon, but is a far safer climber with its long mobile arms.

What then, would drive our protohominid from the trees? A chimpanzee can climb with objects in its hands, but with difficulty. Our protohominid, with its terrestrially adapted feet, would have an even greater problem. The role of trees would be fundamentally altered in the human niche if the hands were not free for climbing. A possible next step was a continuation in the trend for encephalization. Pelvic anatomy dictated a compromise, that of delaying cranial growth to the postnatal period. Increased postnatal encephalization in turn means increasing dependency of neonates upon the mother for locomotion and support. This dependency could have several consequences. It would be increasingly dangerous for a mother with a neonate to climb. There could be dramatic increases in fall rates among small children. It is possible that increasing encephalization of the protohomonids was a primary component in the selective pressures that took humans toward tree substitutes in behavior and technology. By modern standards our protohominid infants could be quite precocious and still find the trees a dangerous place. Humans are still good climbers, but there is a long period in every child's development during which locomotor skills do not include effective climbing. Unlike objects, a dependent infant can not be discarded to free one's hands for climbing.

Answer 2

Because standing and walking on two legs freed up our hands to use tools for hunting ,obtainging food, and defending ourselves. our ability to use tools is one of the things that sets us apart from the rest of the animal kingdom.

Answer 3

I believe it may be incorrect to suggest it is only in the human lineage since it is in the Australopithecines and might be in chimp and even gorilla (not recommended to put in class response).  Bipedalism is a defining characteristic of humans.  It used to be much more important until they discovered other closely related apes which were bipedal.

Answer 4

Because tricycles are regarded generally as slower.  However they ARE more and more popular among Floridians.