Iconoclastic
If so, why only some species would abandon asexual reproduction in favor of more costly and inefficient sexual reproduction?
I can see that I'm gonna regret this but anyways ...
Evolution isn't meant to be pretty, efficient or even any better than the babble. Evolution is a random process which relies on random change where the fittest survive and the weakest die. That way, a biological entity is able to adapt and change as its environment does.
I've said it before and I'll say it again. What kind of creator chappie puts a woman's pleasure beach next to her sewage works? A creator doesn't. At least a good one doesn't. Also, who in the right mind designs DNA that way such that when it mutates, it could give rise to cancer? Man evolved. The design ain't pretty. It ain't efficient but it works - just.
Science hasn't got all the answers - YET. But it will. Just because it doesn't have the answers yet, doesn't mean we got her via some sky wizard - which is so preposterous, it's positively laughable.