Hypermorphosis in Irish Elk (Megaloceros)
The 13' antler
rack in Megaloceros was in the past argued to be an
example of Orthogenesis,
continued evolutionary increase in size of a structure past the
point where it is adaptive. Thus it was argued that the species
had become extinct because its body was no longer able to support
the weight its antlers. Some scientists explained the extinction
of dinosaurs in the same way. SJ Gould showed instead that deer
antlers in general are positively allometric with respect
to body size [measured here as height at the shoulder]. That is,
antlers of Megaloceros have
the expected size for a species of its size (left), and requires
no special explanation. The same relationship holds within
species, such that larger Megaloceros have proportionately larger antlers than smaller (right).