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Todd H. Oakley added 2.2.2.tex
almost 10 years ago
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\indent While the gradual-morphological model of eye evolution is grounded in microevolutionary thinking, macroevolutionary fields like phylogenetics also often ignore origins. By focusing on the distribution of complex traits in different species, phylogeneticists often gain important insights into the timing of evolutionary events. But when they score such traits as simply absent or present, they cannot gain insights into how traits originated because they implicitly assume all components of the trait evolve in concert. For example, armed with a phylogenetic tree, an evolutionist might score species as ‘eyed’ or ‘eyeless’, to infer the number and/or timing of eye gains and losses \cite{Oakley_2002}{e.g. Oakley, 2002; Fig. 1}. Based on assumptions like parsimony or maximum likelihood, he then may suggest that character states scored in living species can be inferred in common ancestors, leading to inferences of trait history as series of all-or-none gains and losses. Even if the separate components of multi-part systems have different evolutionary histories, scoring complex traits as simply present or absent makes inferring separate histories for components impossible. The inference of all-or-none gains and losses can be said to impose a punctuated mode of evolution, such that all components of a complex trait originate or become extinct simultaneously, but see \cite{Marazzi_2012} for an alternative phylogenetic model.
