A coevolutionary arms race takes place in a predator-prey relationship when the
prey evolves a new defense or the predator evolves a new offense. Each species
will evolve a new trait to give them an advantage over the other. When this
process occurs with several new adaptations over a short period of time, it is
known as a coevolutionary arms race.
Coadaptation may arise from coevolution, the development of traits in two
species in direct relation to each other. However, coadaptation may also occur
as a result of two species developing traits independently of each other that
then happen to make the species well adapted to each other.