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Re: Quo vadis AAAARG metaphor limits




On Fri, 9 Feb 1996, Pat Grant (Library: Serials Catalog wrote:

> I think we need a new metaphor--the bush just isn't up to the level of
> the discussion that's being hung on it.  How about trying, say, a
> copse of poplar trees?  Those are normally all clones of one tree,
> spread by underground stems, but once established each tree can
> function as an individual.  Is this a great metaphor or what!
> 

        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.
 But even at the species level, what about hybrids, 
subspecies, chain-species, etc.? There's even been some talk about species 
arising through hybridization, based on the finch studies in the 
Galapagos, so there goes our branching analogy again. Life doesn't just 
branch, it rejoins branches back together. I don't know what an 
appropriate metaphor would be. I know corals can branch and then the 
branches can merge again, but the "coral of life" just doesn't have the 
ring, appeal, or common imagery of a tree. The problem is, there are 
shortcomings with this damn metaphor, and these shortcomings in a 
metaphor can encourage shortcomings in our understanding of evolution.  

        -nick L.