The researchers then compared four models of speciation to determine which best accounted for the rate of speciation actually found. The Red Queen hypothesis, of species arising as a result of an accumulation of small changes, fitted only eight percent of the evolutionary trees. A model in which species arise from single rare events fitted eighty percent of the trees.
Dr Pagel said that the research shows speciation is the result of rare events in the environment, such as genetic mutations, a shift in climate, or a mountain range rising up. Over the long term new species are formed at a constant rate, rather than the variable rate Pagel's team expected, but the constant rates are different for different groups of species.
The work suggests that natural selection may not be the cause of speciation, which Pagel said "really goes against the grain" for scientists who have a Darwinian view of evolution. The model that provided the best fit for the data is surprisingly incompatible with the idea that speciation is a result of many small small events, Pagel said.
The paper is published in the journal Nature.
More information: Venditti, C., Meade, A. & Pagel, M. Nature advance online publication (2009); doi:10.1038/nature08630
It still doesn't satisfactorily explain how bird wings could come to be out of land-dwellers when generations upon generations would have to endure useless not-arms/not-wings until the first flight-ready version emerged (or where they all penguin-like first?) but this does explain why we don't see a continuum of unfit species on the egress everywhere we look, at least not until some cataclysm (like man) befalls them.