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Re: Quo vadis AAAARG metaphor limits



In a message dated 96-02-09 13:22:22 EST, longrich@phoenix.Princeton.EDU
(Nicholas R. Longrich) writes:

>       The biggest single problem with the tree metaphor is that it 
>includes _only divergence_ and the phylogenetic tree has a hell of a lot 
>of very interesting examples of branches coming back together- eukaryotic 
>cells, for example, which are comprised of a host cell, aerobic bacteria 
>(mitochondria) b-g algae in the case of plants (chloroplasts) and perhaps 
>something else that made up the centrioles. Or look at lichens, for that 
>matter- branches of eukaryotes coming together. Somewhat less compelling 
>examples come from things like corals and giant clams that keep algae in 
>their tissues, or animals and digestive bacteria. But if you bring in 
>sexual reproduction, what you have is a recombination of branches, 
>branches coming back together,if you look close enough. At the 
>individual level, each of us would be a branch, every time we have a kid 
>with somebody, that's a joining of branches- you know, how the Family 
>Tree of a person branches out rather than narrowing down as you go back 
>in time, as it generally does with species.

Reticulate evolution seems to rare enough among vertebrates that it may
safely be ignored, particularly above the species level. Most cladistic
computer programs are poorly equipped to deal with it.