Despite his tragically short life (1930-1972) and brief career, Robert MacA
rthur was perhaps the most influential ecologist of the 20th Century. With
the possible exceptions of Charles Elton and Eugene Odum, no other ecologis
t had as much influence during his lifetime or left such an enduring legacy
. MacArthur's influence stems not only from his substantial and frequently
cited published works but also from his direct personal interactions and co
llaborations with contemporary scientists, especially young people. He comb
ined his facility for mathematics and his knowledge of natural history to d
evelop a body of ecological theory that set the direction of evolutionary e
cology during his career and in the decades since his death. Much of his wo
rk was inspired by very general statistical patterns of abundance, distribu
tion, body size, and diversity of species. To explain these patterns, he de
veloped simple mathematical and graphical models. In the 25 years since Mac
Arthur's death, the limitations of his models have been revealed, but the e
mpirical patterns that inspired them remain poorly understood. Accumulation
of new data has allowed these statistical "macroecological" patterns to be
quantified more precisely and has shown them to be nearly universal. They
remain vexing puzzles waiting for solution-manifestations of general ecolog
ical laws that are still waiting to be discovered.