Self-study
The common ancestors of Australian land- and tree-dwelling kangaroos had prehensile (grasping) tails and long opposable thumbs, attributes that are well-adapted to tree-dwelling but offer kangaroos few advantages on land. ██ ██ ██████ ███████████ ██████████ ████ █████████████ █████████ ██████████ ████ █████ ███████████ ████ ██ ████████ ██ ███ ████ ████ ███ ██████ █████████████ █████████ ███ ████ ████ ██ █████
"Surprising" Phenomenon
What caused modern tree-dwelling kangaroos to lose traits of their ancestors that were well-suited for life in trees?
Objective
The right answer will be a hypothesis that offers a similarity between land- and tree-dwelling kangaroos. This similarity will explain why modern tree-dwelling kangaroos, like their land-dwelling counterparts, lost the prehensile tails and opposable thumbs of their ancestors, even though these traits are well-adapted to tree-dwelling kangaroos’ lifestyles.
14.
Which one of the following, ██ █████ ████ █████ ███████ ███ ████████ ████ █████ ██████
a
Modern tree-dwelling kangaroos ████ ████ ████ ████ ██████ ██████ ███ ██████████ ███ ███ ██████ █████████ ██ ██████ █████ ███ █████████████ █████████ ████ █████ █████████ ██████ ██ ███████ █████ ███████ ██████████
This does not help explain the puzzling fact. (A) says that modern tree-dwelling kangaroos must descend tree trunks more slowly than their ancestors, presumably because they lack opposable thumbs, without explaining why they lost this trait.
b
Modern tree-dwelling kangaroos ███ ███████ ████ ████ ██████ █████████████ █████████ ███ ██████ ████ █████ ██████ ██████████
This does not help explain the puzzling fact. (B) discusses size, which is not one of the traits the stimulus discusses as being beneficial for a tree-dwelling lifestyle. Furthermore, (B) offers a difference between land- and tree- dwelling kangaroos, not a similarity.
c
Modern tree-dwelling kangaroos' █████ ██████ █████ █████████ ███ ████ ███ ████████ ██████ ███ ████ ████████ ████ █████ ██ ██████ █████████████ ██████████
(C) offers a difference between land- and tree- dwelling kangaroos, not a similarity. The difference in length and flexibility of the kangaroos’ tails is not helpful for explaining the puzzling fact in the stimulus.
d
Modern tree-dwelling kangaroos ███ █████████ ████ ███████ ██ █████████████ █████████ ████ ███ ████ █████████████ ███ ████ ███████████ ██████ ██████ █████████████ █████████ ███████ ██ ████████
(D) says modern land- and tree-dwelling kangaroos share a similarity: in addition to sharing a common ancestor, they both evolved from land-dwelling kangaroos. This explains why modern tree-dwelling kangaroos lost some of their earlier ancestor’s beneficial tree-dwelling traits.
e
Modern tree-dwelling kangaroos ████ ███████ ███ ██████ ████ ████ ████ ██████ █████████████ ██████████ ███ ████ ████ ████ ██████ ██ ████ ████ ██ ██████ █████████████ ██████████
(E) offers a difference between land- and tree- dwelling kangaroos, not a similarity. The difference in the size and strength of the kangaroos’ hind legs is not helpful for explaining the puzzling fact in the stimulus.