The enormous complexity of the human brain stems not from the sheer number of genes, but from the nature of those genes. If genes were like pixels in a digital photograph - an idea suggested by the common metaphor of genomes as "blueprints" - 25,000 genes really wouldn't suffice. But genes don't really work that way. They aren't pixels - they're instructions, each one something like an IF-THEN in a line of a computer program. As every computer programmer realizes, even a small number of IF-THENs interacting with one another can lead to enormous complexity. (That's why debugging is hard and only gets harder as the size of computer programs increases.)