One method of dating the emergence of species is to compare the genetic material of related species. Scientists theorize that the more genetically similar two species are to each other, the more recently they diverged from a common ancestor. After comparing genetic material from giant pandas, red pandas, raccoons, coatis, and all seven bear species, scientists concluded that bears and raccoons diverged 30 to 50 million years ago. They further concluded that red pandas separated from the ancestor of today’s raccoons and coatis a few million years later, some 10 million years before giant pandas diverged from the other bears.
Which one of the following can be properly inferred from the passage?
OPTIONS[A]. Giant pandas and red pandas are more closely related than scientists originally thought they ere.
[B]. Scientists now count the giant panda as the eighth species of bear.
[C]. It is possible to determine, within a margin of just a few years, the timing of divergence of various species.
[D]. Scientists have found that giant pandas are more similar genetically to bears than to raccoons.
[E]. There is substantial consensus among scientists that giant pandas and red pandas are equally related to raccoons.
Explanation:
more recently they diverged from a common ancestor. Then we get a specific case study— some conclusions based on this rule. Scientists figure that first bears and raccoons diverged, then red pandas diverged from raccoons, then giant pandas diverged from bears. What can we infer? Well, the scientists concluded that giant pandas diverged from bears more recently than they diverged from raccoons (i.e. they diverged from raccoons along with all the other bears before they diverged from the other bears). According to the rule, therefore, scientists must have observed (D), the fact that giant pandas are more genetically similar to bears than they are to raccoons.
(A) We have no idea what scientists “originally thought” about the genetic relationship between giant pandas and raccoons, so we can’t infer (A).
(B) We’re told that giant pandas “diverged” from other bears millions of years ago; that gives us no reason to infer that scientists therefore consider them a species of bear.
(C) The stimulus speaks of divergences occurring “a few million years later” and “30 to 50 million years ago”; that certainly does not qualify as establishing the timing “within a few years.”
(E) Since bears (including the ancestors of giant pandas) diverged from raccoons a few million years before red pandas did, we would expect red pandas to be more closely related to raccoons genetically than are giant pandas.
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