Thus, for example, elephants have smaller and fewer broods than mice, but longer lifespan and gestation.[3] Rules like these concisely organized the sum of knowledge obtained by early scientific measurements of the natural world, and could be used as models to predict future observations. Among the earliest biological rules in modern times are those of Karl Ernst von Baer (from 1828 onwards) on embryonic development,[2] and of Constantin Wilhelm Lambert Gloger on animal pigmentation, in 1833.[3] There is some scepticism among biogeographers about the usefulness of general rules. For example, J.C. Briggs, in his 1987 book Biogeography and Plate Tectonics, comments that while Willi Hennig's rules on cladistics "have generally been helpful", his progression rule is "suspect".[6]