The argument from design has played an important role in the history o
f philosophy and biology. Paley, the 19th-century theologian, was stru
ck by the bodily complexity and adaptive fit of animals to their envir
onments; he used the argument from design to prove the existence of Go
d. Darwin, however; provided the natural evolutionary mechanisms that
eliminated the need for positing a divine creator to explain the struc
ture of animals; he was thus able to treat the historical problem of o
rganic evolution by providing a historical solution. Today, some stude
nts of behavior are similarly struck by the complexity of animals' act
ions and their adaptive fit to the environment. Like Paley, they use t
he argument from design, brit to prove the existence of a conscious de
signer inside the head of the animal-the mind. This mentalistic approa
ch suffers from many of the philosophical and empirical problems that
plagued similar efforts in the past.