Its just another, and more humorous, way of saying that our behavior is determined not just by reason (our personal psychology), but by physical, biological, cultural and social factors that are molded mostly by natural selection and other purely random processes. Once you understand that, the human world makes perfect sense.

For example. Why do most people love kids? Because people who don't like kids do their best to avoid having any, so they don't pass their dislike of kids on to their own children. Its inevitable you will wind up with a population that, for the most part, loves children. Or think they do. Morality, or "human decency" (whatever that is) have nothing to do with it.

God doesn't work in mysterious ways, he works in random, but statistically predictable ways, just like quantum physics. This is what Charles Darwin stumbled on over a century ago. That's why he is so hated. We don't like knowing that about ourselves.