(Levins, Lewontin, 1985, p. 287) Many biologists and historians of the life sciences would follow Georges Canguilhem in recognizing the mechanism of regulation as the "supreme biological fact" (Canguilhem, 1974, p. 3, our translation). Even so, we are far from having a consensus about how we should conceptualize these factswitness the diverse notions that have succeeded each other in the course of the 20th century : the constancy of the milieu intérieur (Bernard, 1872) ;