Dopamine is a neurotransmitter that seems to have been around from about the time of the very first nerves. Every animal we’ve looked at, including some that branched off prior to the Cambrian, seems to express the dopamine signaling machinery in its nerves. So you might expect that eliminating dopamine entirely would be a fatal step. But, at least when it comes to everyone’s favorite fruit fly, Drosophila melanogaster, that’s not the case. Flies that apparently lack dopamine signaling manage to live just as long as their peers. They do, however, end up turning into lethargic masochists.