asexual reproduction widespread

Hello biokiki,
Well for starters, in animals, there is a requirement for genetic diversity to pass on alleles or genes down through generations to come.  Because asexual reproduction does not involve male and female gametes, it will basically be producing clones of the organism, identical copies with no genetic recombination with all the mixing of genes that takes place.
Even though asexual reproduction usually requires less energy, occurs more rapidly and involves one parent, sexual reproduction is the one that aids evolution and is more efficient, producing hybrid generations and balancing out the gene pools.
I hope this helps

It doesn't promote species diversity. Remember, in sexual reproduction, you have a mixing of alleles. In asexual reproduction, the daughter cell has the exact copy of its parent.