What must happen for speciation to occur?
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a. gene flow must increase.
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b. a population must be isolated in some way.
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c. all alleles in the population must become fixed.
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d. asexual reproduction must occur.

B. A population must be isolated in some way.

Explanation:

B. A population must be isolated in some way.

Explanation:

I got it right :p

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.