What are some reasons why some organisms can reproduce both sexually and asexually?

Asexual versus Sexual Reproduction

However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.

Explanation:

Sexual reproduction provides greater genetic variation, as it combines the DNA from two parents, producing offspring that are not genetically identical to either parent. Asexual reproduction requires only one parent and produces offspring that are genetically identical to the parent.

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the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.

the fossil record provides evidence of a common ancestor to many species.