The younger brother of the British statesman Earl Balfour, Francis Balfour's career was cut short when, while convalescing from typhoid fever in Switzerland, he died attempting an ascent of the Aiguille Blanche, Mont Blanc. Balfour, who was born in Edinburgh, held the position of animal morphologist at the Naples Zoological Station and in 1882 was appointed to the specially created post of professor of animal morphology at Cambridge University. Much influenced by the work of Michael Foster, with whom he wrote Elements of Embryology (1883), Balfour showed the evolutionary connection between vertebrates and certain invertebrates, both of which have a notochord (a flexible rod of cells extending the length of the body) in their embryonic stages. Similar research was being conducted at that time by Aleksandr Kovalevski. Balfour proposed the term Chordata for all animals possessing a notochord at some stage in their development, the Vertebrata (backboned animals) being a subphylum of the Chordata. He was an early exponent of recapitulation – the theory that ancestral forms are repeated in successive embryonic stages undergone by modern species. Balfour also did pioneer work on the development of the kidneys and related organs, as well as the spinal nervous system. His other important publications include On the Development of Elasmobranch Fishes (1878) and Comparative Embryology (1880–81) published in two volumes (invertebrates and vertebrates), the latter forming the basis of modern embryological study.