Anthropic principle, probably. But... the universe is filled with water, so that's a likely medium for chemical reactions. And if you want long molecules to ac

Anthropic principle, probably. But... the universe is filled with water, so that's a likely medium for chemical reactions. And if you want long molecules to actually do interesting things, you need carbon in there somewhere. So the most likely chemistry is at least somewhat similar. And for Mars, which is made out of similar stuff as Earth, and periodically trades rocks with us? If there's life on Mars, it probably shares ancestry with you and me.