POTENTIAL BETWEEN BRAINS 239
by workers. Brood care, nest building, and cleaning are all done by other
specialized forms.
It might be tempting to think that these diff er ent castes develop
through diff er ent individuals having diff er ent genes. But there is no such
correlation: the extreme phenotypic specialization arises through devel-
opmental plasticity that is itself under the regulation of the emergent be-
hav iors of the group as a whole. Fertile queens develop from larvae that
have been fed a sugar- rich substance called “royal jelly.” Th e jelly is pro-
duced by workers and contains the hormones that turn larvae into fertile
queens rather than sterile workers. One or more of these bloated queens
subsequently produces all the eggs cared for by workers. During this stage,
the level of care and nourishment the larvae receive determines their
eventual adult form: workers, soldiers, nurses, winged nymphs that be-
come reproductive adults, and so on. Th ese are sometimes called “poly-
phenisms” and are excellent examples of developmental epige ne tics.
Bees, ants, and termites are famous for their striking organ ization and
highly effi cient responses to everyday challenges. Much of that is achieved
through chemical messages called “pheromones.” Depending on species,
there are about ten to twenty diff er ent pheromones, and all individuals
are sensitive to them. Some pheromones can quickly summon up thou-
sands of ants to a food discovery. Others can signal attacks on prey, the
defense of the colony, or even the relocation of the colony. Still others
help ants distinguish among diff er ent family members, nest mates, and
strangers. Th e queen also has special pheromones that infl uence workers’
be hav iors.
Pheromone following has been best described in ants’ trail laying to
food. When a forager fi nds a food source, it heads back to the nest, leav-
ing a trail of pheromone that other ants can follow. Aft er feeding, in turn,
each recruit reinforces the pheromone trail. Th e result is a nonlinear
increase of ants around the food source and a more effi cient utilization of
it. Such self- organized responses are even more impressive in activities
like nest building, with a complex topology of underground galleries
housing treelike networks of tunnels and chambers.
So how does the result become greater than the sum of its parts? Aft er
all, the complexity of nest form is not within the cognitive potential of
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