Walter Heape was a prominent 19th century British physiologist who made several significant contributions to science [Biggers, 19913, including the first successful embryo transfer experiments [Heape, 1890; Heape, 1897al and the most often quoted definition of estrus [Heape, 19001. Heape's embryo transfer experiments were the harbingers of present day in vitro fertilization and gamete intrafollicular transfer. They were also conceptually provocative, suggesting that genetic influences could be differentiated during development from those of the maternal uterine environment. His definition and discussion of estrus, which is the focus of this short historical review, are especially relevant to primatologists today because of the ongoing controversy regarding the applicability of this concept to the sexual behavior of female primates [Goy, 1992; Nadler, 1992a, bl. Frank Beach 119811 once wrote "Unless a scientist is familiar with the history of his subject, he can neither avoid the errors of his predecessors nor profit fully from their successes" (p. 327). As Beach further pointed out, part of the reason that an historical perspective may advance a research area is that some of the issues we investigate today were originally conceived and competently discussed years before we were born. Thus it is with Walter Heape's legacy to primatology, his definition of estrus, as it relates to the Primates.
Heape was born in 1855, the son of a wealthy merchant, who briefly pursued a business career before beginning a career in science at Trinity College, Cambridge, in 1879. He traveled widely, both before and after entering advanced graduate study, including a stay of several months in India. There he studied embryonic development and uterine changes during the menstrual cycle in rhesus monkeys at the Calcutta Zoo [Heape, 1897b, 18981. It was during studies on the rhesus monkey in India and later in Cambridge that Heape developed the insights for his important theoretical contribution on the subject of estrus.
The course of Heape's career undoubtedly would have gone quite differently were it not for two crucial events which occurred in the midst of his graduate training [Biggers, 19911. The first was the death of his mentor in embryology, F.M Balfour, who died in 1882 at the age of 32 from a fall while mountain-climbing in Switzerland. Although Heape continued his studies in embryology for a time under Balfour's successor, he subsequently renewed an earlier interest in marine biology, and played a major role in the establishment of the Plymouth Laboratory, a scientific research station designed to promote the interests of the British fishing