One of the many questions naturalism finds difficult to answer given a Darwinian paradigm is why sexual reproduction would have ever evolved when asexual reproduction works perfectly well for so many organisms. Sexual reproduction is incredibly complex, so much complicated chemistry has to occur at just the right time, and so many contingencies have to be perfectly synchronized that it's simply extraordinary that both plants and animals would've evolved such an improbable means of perpetuating themselves.
One explanation for this phenomenon that's sometimes heard is that the genetic mixing that results from sex promotes diversity which in turn promotes adaptation which advances the evolutionary process.
Perhaps so, but one problem with this explanation is that, though it might explain why sex is evolutionarily advantageous, it doesn't explain how it could've arisen in the first place.
The excellent video that follows gives an idea of the complexity of the process, but even this elides the incredible challenge of evolving meiosis, sex organs, the complicated chemical reactions that occur throughout the process, and much, much more.
Complicated systems with which we're familiar are always the product of intelligent engineering and design, but naturalists insist that blind processes like genetic mutation and sheer chance could've done the job of producing sex. I suppose they could've but to believe that they actually did requires an enormous investment of blind faith in serendipity.
Watch:
