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:

Speciation refers to the origin of new species from a pre-existing species.Speciation can be Gradual or instantaneous depending on the time taken for evolution of new species.Speciation occurs when gene pool of a population is somehow reproducively isolated from other populations of parent species.This isolation can occur by geographical barrier, reproductive isolation or non-recognition of potential mates.Speciation can be classified as allopatric speciation, Sympatric speciation and parapatric speciation.

Ithink its because more have died recently than in the past.