Looking for your best argument for evolution/against creation.

Not exactly. But you're on to something. Genetic variation means that there's a greater chance that someone in a population will survive. If the environment changes, then a population or species that has greater inherent genetic diversity has a better chance of making it through the environmental change.
But, for the most part, the environment doesn't change, at least not much, over the lifetime of an individual organism. Think about a raccoon. They're pretty awesome little creatures--smart, mean, and very well-adapted for the environment they currently live in. Most raccoons survive, at the most, eight or ten years. The environment is unlikely to change much over that time, or over ten times that time. If you think about it, they'd seemingly be better off if they didn't have genetic variation, since they're already supremely adapted for the current environment. So why is genetic variation important? It's because of the evolution of pathogens. The genetic variation provided by sexual reproduction is the only thing that gives organisms a chance to stay out in front of the rapid evolution of germs. If it weren't for the evolution of bacteria and viruses, evolution of raccoons--and humans--would be counter-productive. There would be no need for sex. The environment--except for pathogens--changes slowly enough that the little bit of evolutionary change provided just by mutation would probably be enough to allow organisms to adapt to changes.

So--long story short--the only reason to have sexual reproduction is to be able to evolve fast enough to respond to evolution of germs. Our external genitalia is part of our sexual reproduction machinery--we wouldn't need it if we reproduced asexually like many organisms (including some complex animals). Our enemies evolve incredibly fast, so the extra evolution provided by sex is the only way we can keep up. Without evolution, sex is a bad thing. So, any time somebody tells you they don't believe in evolution, take your dick out and wave it at them.

/r/DebateAnAtheist Thread