He wrote about many, many things. He was a one-in-a-million thinker.
For those that care to learn more and maybe, possibly expand your mind just a tad:
http://www.freethought-web.org/ctrl/...hen_gould.html
One of his more famous pieces of insight was (and I'm paraphrasing drastically here) that humanity is not the end all of evolution. We are merely a twig in a huge tree that just happen to develop, purely by chance, into life as we know it today. And if you replanted the same seed from which the tree sprouted, there's virtually no chance it would grow the same way again.
In other words, our very existence is based entirely on dumb luck. The dinosaurs' reign ended because of dumb luck. Ours could end just as easily. Make each day count.