Inferring and Explaining

Te fossil record, particularly inDarwin’s time, was abit of a two-edged sword. Critics complained that if descent with modifcation was true, there should be a fossil record of these “transitional forms.” Darwin wisely conceded the force of this objection but also ofered a very sophisticated explanation of howdifcult it is for fossils to form and why gaps in the record were inevitable. The Scala Naturae , or the Natural System A widely held view in the century before Darwin postulatedaverydiferent kindof order to thebio- logical world. According to the scala naturae (scale of nature), life was static but hierarchical. Tere was an observable and classifable progression fromthe simplest andmost primitive forms of life to the most complex and advanced. Tis view had been pretty thoroughly rejected by the time Dar- win began hiswork. But a remnant of it remained at the heart of biology. Itwas nowunderstood that though the structure wasn’t hierarchical, there was a structured order to life nonetheless. From the frst dawn of life, all organic beings are found to resemble each other in descending degrees, so that they can be classed in groups under groups. Tis classifcation is not arbitrary like the grouping of stars in constellations. 4 Any intelligent four-year-old cango to the zoo and recognize that the diferent feline species in the cages are all cats, just like Boots at home. Feline species around the world are “related” to each other, and they are more “closely related” to each other than they are to canine species liv- ing in the same environment with them. Nature seems to sort itself out into one giant natural system . 71 Te obvious question is why do we observe the following? e 3 . The natural system Darwin’s answer was unequivocal: Te real afnities of all organic beings are due to inher- itance of community of descent. Te natural system is a genealogical arrangement, in which we have to dis- cover the lines of descent by the most permanent char- acters, however slight their vital importance may be. 5 Patterns of Geographical Distribution Darwin was fascinated by the connection between life and where that life was found on this earth. Before Darwin, the only viable expla- nation of this connection was that God chose to put it there. Darwin is the founder of modern, causal biogeography. 6 And biogeographical facts are, perhaps, the most widely used evidence in On the Origin of Species . darwIn and Common desCent e 4 . Patterns of geographical distribution Let’s start with a macro question. If an omni- scient and all-loving God deliberately created each species to ft perfectlywith its environment, why do we see such diversity in virtually identi- cal climates between the Old and NewWorlds? If we travel over the vast American continent, from the central parts of the United States to its extreme southern point . . . Tere is hardly a climate or condi- tion in the Old World which cannot be paralleled in