The historian of biology Peter J. Bowler has written that devolution was taken seriously by proponents of orthogenesis and others in the late 19th century who at this period of time firmly believed that there was a direction in evolution. Orthogenesis was the belief that evolution travels in internally directed trends and levels. The paleontologist Alpheus Hyatt discussed devolution in his work, using the concept of "racial senility" as the mechanism of devolution. Bowler defines "racial senility" as "an evolutionary retreat back to a state resembling that from which it began."