2019年9月7日托福阅读真题+题目+答案：The Formation of New Species

2019年9月7日托福阅读真题+题目+答案：The Formation of New Species

Speciation is the process by which new species form. It begins with the isolation of two populations. If two populations are to become sufficiently distinct that interbreeding is difficult or impossible, then there must be relatively little gene flow (migration) between them (because if there were a great deal of gene flow, then genetic changes in one population would soon become widespread in the other as well). However, it is not enough for the two populations to simply be isolated; they will become separate species only if, during the period of isolation, they evolve sufficiently large genetic differences. Thus the second factor in species formation is genetic divergence. The genetic differences must be large enough that if the isolated populations are reunited, they can no longer interbreed and produce vigorous, fertile offspring. If isolated populations are small, chance events may generate significant genetic differences by genetic drift (changes in the frequency of a characteristic in a population caused by chance rather than reproductive fitness). In both small and large populations, different environmental pressures in separate environments may favor the evolution of large genetic differences.

1. The word “vigorous” in the passage is closest in meaning to

A) normal

B) strong

C) similar

D) numerous

2. According to paragraph 1, if gene flow between two populations is unrestricted, then

A) speciation will inevitably occur

B) the size of the populations will increase

C) genetic differences between the two populations will increase

D) changes in one population will spread to the other

3. Paragraph 1 implies that the defining factor in determining whether two populations belong to the same species is whether they

A) can interbreed and produce vigorous, fertile offspring

B) occupy the same geographic area

C) share common ancestors

D) are subject to the same environmental pressures

Speciation has seldom been observed in the wild. Nevertheless, evolutionary biologists have synthesized theories, observations, and experiments to devise hypothetical mechanisms for the origin of new species. These mechanisms fall into two broad categories: (1) allopatric speciation, in which two populations are geographically separated from one another, and (2) sympatric speciation, in which two populations share the same geographical area.

4. The word “seldom” in the passage is closest in meaning to

A) rarely

B) directly

C) certainly

D) commonly

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