本题目来源于试卷: Evolution & Extinction，类别为 IB环境系统与社会
[单选题]
Figure: Tuskless fem 7xmpppe- c7/s2i;n q yft.y 5 ubn:0pts7r 7,xa iov/iale elephants in Gorongosa
Both male and female African elephants (Loxodonta africana) are usually born with tusks. It has been observed that in Gorongosa National Park, Mozambique, some female elephants are born without tusks.
Suggest how natural selection explains the trend shown in the graph.
A. Elephants broke their tusks while fighting, and their offspring were born without tusks.
B. Poachers hunted elephants with tusks, resulting in increased survival of elephants without tusks.
C. Elephants born without tusks are better fighters so survived better.
D. Mutations resulting in no tusk formation started to happen more often.
参考答案: B
本题详细解析:
Option B is correct because poachers hunted elephants with tusks for ivory, ty4g)5 y x/pf7is is /jt0vx k1x+rh+fqhus removing animals with the biggest tusks from the breeding population. Elephants born with the mutation of no tusks survived and were able to reproduce, increasing the number of individuals in the population with the “no-tusk” gene. This is an example of natural selection in response to a selph1f q +is gyxxi)fjv4r+7 xk 0sy/5t/ective pressure.
Option A is incorrect as an elephant breaking its tusk would still pass on the genes for tusk formation to its offspring.
Option C is incorrect as elephants born with tusks would be better fighters.
Option D is incorrect because it's natural selection which is most likely to change the proportion of variants in a population and not mutation.
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