Question

inferences
one theory behind human bipedalism speculates that it originated in a mostly
ground - based ancestor that practiced four - legged \knuckle - walking,\ like
chimpanzees and gorillas do today, and eventually evolved into moving
upright on two legs. but recently, researchers observed orangutans, another
relative of humans, standing on two legs on tree branches and using their
arms for balance while they reached for fruits. these observations may
suggest that ______

which choice most logically completes the text?

choose 1 answer:

a bipedalism evolved because it was advantageous to a tree - dwelling
ancestor of humans.

b bipedalism must have evolved simultaneously with knuckle -
walking and tree - climbing.

c moving between the ground and the trees would have been
difficult without bipedalism.

d a knuckle - walking human ancestor could have easily moved
bipedally in trees.

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Explanation:

The original theory links bipedalism to a ground - based, knuckle - walking ancestor. But orangutans (a human relative) were observed using bipedalism in trees. Option A suggests bipedalism evolved for a tree - dwelling ancestor, which fits the new observation as it offers an alternative origin for bipedalism. Option B's "must have evolved simultaneously" is too strong and not supported. Option C's claim about moving between ground and trees is not related to the orangutan observation. Option D's "easily moved bipedally in trees" for a knuckle - walking ancestor is not supported by the text.

Answer:

A. bipedalism evolved because it was advantageous to a tree - dwelling ancestor of humans.