Fruit flies are "little people with wings" goes the saying in the scientific community, ever since the completion of the Human Genome Project and its revelations about the similarity amongst the genomes of different organisms. It is humbling that most signalling pathways which "define" humans are conserved in Drosophila, the common fruit fly.

Feed a fruit fly caffeine and it has trouble falling asleep; feed it antihistamines and it cannot stay awake. A C. elegans worm placed on the antidepressant flouxetine has increased serotonin levels in its tiny brain. Yeast treated with...