The concept of heterotopy, bringing evolution about by a change in the spatial arrangement of some process within the embryo, was introduced by the German zoologist Ernst Haeckel in 1866.
With the arrival of evolutionary developmental biology in the late 20th century, heterotopy has been identified in changes in growth rate; in the distribution of proteins in the embryo; the creation of the vertebrate jaw; the repositioning of the mouth of nematode worms, and of the anus of irregular sea urchins.
[2][4] The evolutionary biologist Brian K. Hall argues that heterochrony offers such a simple and readily understood mechanism for reshaping bodies that heterotopy has likely often been overlooked.
One textbook example of heterotopy in animals, a classic in genetics and developmental biology, is the experimental induction of legs in place of antennae in fruit flies, Drosophila.
This further demonstrated that structures that were thought to be homologous at one time and were later modified still retained some modularity, or were interchangeable even millions of years after evolution had sent antennae down a separate path than the other appendages.
The Himalayan rabbit and the Siamese cat are examples of artificial selection on heterotopy, developed by breeders incidentally long before the concept was understood.
The current theory is that people selected for stereotypical phenotypic patterns (dark extremities) that happened to be repeatedly produced given a typical temperature.