Recently on this blog, I have been exploring and examining some of the genomic arguments for common descent. As I have been documenting in recent weeks, while the case for common ancestry — on the face of it — looks mightily strong, closer inspection reveals that the arguments don’t, in fact, stand up under more rigorous scrutiny. In the vast majority of instances, the corroborative data is very carefully cherry picked from the pertinent data set, and the non-congruent evidence is discarded or ignored. In some cases, non-congruent data is rationalised — sometimes plausibly. But then one ought not to think that an ad hoc rationalisation constitutes evidence for said position. As Casey Luskin notes,
…at the end of the day, we must call them what they are: ad hoc rationalizations designed to save a theory that has already been falsified. Because it is taken as an assumption, evolutionists effectively treat common ancestry in an unfalsifiable and unscientific fashion, where any data that contradicts the expectations of common descent is simply explained away via one of the above ad hoc rationalizations. But if we treat common descent as it ought to be treated — as a testable hypothesis — then it contradicts much data.
One popular argument for common descent is the case from the discipline of biogeography — that is, the study of the geographical and historical distribution of species in relation to one another. The argument is based largely around the observation that species are related in accordance with their geographical proximity with respect to one another. One well-known example of this is the concentration of marsupial mammals in Australia and South America. As the Internet encyclopedia, Wikipedia, explains,
The history of marsupials also provides an example of how the theories of evolution and continental drift can be combined to make predictions about what will be found in the fossil record. The earliest marsupial fossils are about 80 million years old and found in North America; by 40 million years ago fossils show that they could be found throughout South America, but there is no evidence of them in Australia, where they now predominate, until about 30 million years ago. The theory of evolution predicts that the Australian marsupials must be descended from the older ones found in the Americas. The theory of continental drift says that between 30 and 40 million years ago South America and Australia were still part of the Southern hemisphere super continent of Gondwana and that they were connected by land that is now part of Antarctica. Therefore combining the two theories scientists predicted that marsupials migrated from what is now South America across what is now Antarctica to what is now Australia between 40 and 30 million years ago. This hypothesis led paleontologists to Antarctica to look for marsupial fossils of the appropriate age. After years of searching they found, starting in 1982, fossils on Seymour Island off the coast of the Antarctic Peninsula of more than a dozen marsupial species that lived 35-40 million years ago.
I must confess that I have my doubts with regards the efficacy of this argument in establishing universal common descent, or even common descent of all marsupial mammals. After all, as noted in the textbook Explore Evolution, marsupials are not even restricted to the southern continents of Australia and South America. Some marsupials live in the northern hemisphere, and there is even some paleontological evidence for the oldest marsupials inhabiting China!
But be that as it may. As with the majority of arguments favouring common descent, the argument from biogeography is loaded with carefully cherry-picked data.
Read More ›