Annual Review of Entomology
Modern biologists do not look for a point in time at which any particular large taxonomic group of organisms made its appearance on the world scene. Instead, a necessary corollary of neo-Darwinian evolutionary theory is that the several features by which we recognize any such group evolve more or less gradually and not necessarily concurrently. Additionally, it takes time for the numbers of individuals (and species) to build up so that the group becomes recognizable in the fossil record and constitutes an assemblage worthy of separate taxonomic treatment at the higher level which, with the advantages of hindsight, we now recognize that it merits.
Baker, Herbert G. and Hurd, Paul D. Jr., "Intrafloral Ecology" (1968). An. Paper 262.
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