294 - 29+ evidences for Macroevolution The Scientific Case...

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29+ evidences for Macroevolution The Scientific Case for Common Descent Caveats with Phylogenetic Inference As with any investigational scientific method, certain conditions must hold in order for the results to be reliable. A common premise of all molecular phylogenetic methods is that genes are transmitted via vertical, lineal inheritance, i.e. from ancestor to descendant. If this premise is violated, gene trees will never recapitulate an organismic phylogeny. This assumption is violated in instances of horizontal transfer, e.g. in transformation of a bacterium by a DNA plasmid, or in retroviral insertion into a host's genome. During the early evolution of life, before the advent of multicellular organisms, horizontal transfer was likely very frequent (as it is today in the observed evolution of bacteria and other unicellular organisms). Thus, it is questionable whether molecular methods are applicable, even in principle, to resolving the phylogeny of the early evolution of life near the most recent common ancestor of all living organisms (Doolittle 1999 ; Doolittle 2000 ; Woese 1998 ). The list below gives some of the more important caveats that scientists must keep in mind when interpreting the results of a phylogenetic analysis (Swofford 1996 , pp. 493-509). In general, the contribution of each of these concerns will be "averaged out" by including more independent characters in the phylogenetic analysis, such as more genes and longer sequences. Correlated characters:
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This note was uploaded on 11/14/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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294 - 29+ evidences for Macroevolution The Scientific Case...

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