Comte had a high idea of Leroy's contributions to biology and his followers, like Jean-François Robinet, went on drawing attention to his work. Such an appraisal is mainly grounded on methodology. According to positivism, a sound understanding of life has to take account of two elements : not only the organism, but also its environment. Leroy shared the same approach : against Buffon, he argued that the study of animal behaviour had to rely upon observations made in their natural environment. Furthermore, his work is also relevant for sociologists, in as much as the comparison of man to other animals is an important part of the sociological method.

Among the various insights we can gain from Leroy in this last respect, I shall focus on what he says about cooperation and innateness of altruism. Comte, who coined the term altruism, credited Leroy for giving « a definite refutation of metaphysical egoism » (Système de politique positive, III 589). I shall review some of Leroy's observations on cooperation in animals, for instance in hunting, as well as what he says about altruistic behaviour, in order to see how far it supports Comte's claim I just quoted. I shall also show how Comte develops Leroy's ideas, and where he disagrees from him.