Final answer:
The switch from asexual to sexual reproduction in some species when the environment becomes unfavorable is driven by the advantages of genetic variation provided by sexual reproduction.
Step-by-step explanation:
The evolutionary significance of the switch from asexual to sexual reproduction in some species when the environment becomes unfavorable is driven by the advantages sexual reproduction provides. Sexual reproduction allows for greater genetic variation in offspring, which increases the chances of some individuals having traits that can survive and thrive in new or different conditions. This genetic diversity helps the population adapt and evolve to changing environments.
In contrast, asexual reproduction produces offspring that are genetically identical to the parent, limiting the ability to adapt to new conditions. Additionally, asexual populations can grow faster than sexual populations, but the lack of genetic diversity can be a disadvantage when faced with environmental changes.