In his lab at Indiana University, James Goodson keeps violet-
eared waxbills – a stunning but notoriously aggressive type of
finch. Males and females form life-long bonds but they don’t
play well with others. “Most of our animals are housed in male-
female pairs, but were you to introduce another adult into their
cage, most of them would attack immediately,” says Goodson. But
some of Goodson’s birds don’t fit the stereotype. They almost
never attack intruders. These birds weren’t born docile. They
became that way after Goodson stopped a special group of neurons
in their brains from releasing a chemical called VIP. This
single act turned fighters into pacifists and confirmed, in
dramatic fashion, that there’s a special class of cell that
drives aggression in these bird brains. The neurons that Goodson
targeted are found in the hypothalamus – a primitive ball-shaped
region in the centre of the brain that governs many of our basic
functions, from sleep to hunger to body temperature. It also has
a long history with