If human and worm DNA are so similar, why are we so different?

If human and worm DNA are so similar, why are we so different?

There are certain major genes, sometimes called Hox genes and sometimes called developmental genes, that switch on a whole suite of other genes. They are simply like switches in early developmental processes. To give an example that's a little bit closer to home, look for the nearest man and see how different you are from that person. Now although not everything that's different is down to one gene, the fact that you are female and he is male is down to a single gene called SRY. Very early in development, if SRY is present it makes testes, and if it's not, ovaries are made. So you've got just one single gene that switches over from one type to another, and then everything else follows from that, including the hormones produced by testes and ovaries. In worms, they've got a different set of these Hox genes, which start the whole process off. They're switching on a completely different set of genes in a different order, and so the developmental process is utterly different.