In 1996, palaeontologist Mike Benton published a fascinating analysis of tetrapod evolutionary data and concluded: “Competitive replacement has probably played a minor role in the history of tetrapods. In an assessment of the origins of 840 families of amphibians, reptiles, birds, and mammals, fewer than 26%, and probably fewer than 13%, were identified as candidate competitive replacements (CCR’s).” The alternative mechanism proposed was adaptation into new habitats. This finding was presented in the paper as bringing a different emphasis to our understanding of speciation than was brought by Darwin:
“A classic view in evolution has been that many successful radiations of plant and animal groups in the Past have been mediated by competitive interactions. Newly successful groups are said to have outcompeted and displaced the previously established organisms, and hence to have demonstrated some progressive or advantageous feature. [. . .] The pattern of radiation of tetrapods, and indeed of many other groups, suggests that it is unlikely that competitive replacement was paramount.”
For any normal person reading this, the implication is clear: Darwin’s emphasis on selection of hereditable variations is not the key to understanding tetrapod diversification. Recently-published research has strengthened the analysis above, but not all are receptive to the implications. For more, go here.