Friday, March 24, 2006

Phylogeny does not imply morphology (?)   posted by Razib @ 3/24/2006 08:23:00 PM

The fallacy of "ontogeny recapitulates phylogeny" is one of the truisms of our age. I am trying to think of a nice way to get across another idea, that phylogeny does not necessarily imply morphology (or phenotype). In other words, this is the inverse of convergent evolution, where phylogenetically distant kinds exhibit similar morphology because of canalization via the same selective forces in concert with structural constraints. Here I am speaking toward cases where phylogenetically close organisms seem to exhibit extremely differentiated morphologies. Consider the relationship between chimpanzees, humans and gorillas. One line of phylogenetic research implies that gorillas are an "outgroup" to the chimpanzee-human clade, but, to the homocentric mind it seems that our own species exhibits a range of morphological features which set us apart as particularly distinct from our anthropoid cousins. In other words, morphologically one could argue that chimpanzees and gorillas form a phenetic clade,1 while chimpanzees and humans form a phylogenetic clade.

Most long time readers of GNXP know the "back story" to this post. 3 years ago I posted an email from Henry Harpending where he offered that in some cases some human populations exhibit greater phylogenetic similarity (neutral loci) than one would suspect based on physical inspection (due to differences in the adaptive/functional loci). In a broader context it is part of my evolution toward a perspective on species concepts which resembles that of botanists, species are nominal notions we use to verbally indicate clusters of alleles and particular densities in genetic parameter space as opposed to something real. Over the next few years I suspect that the postgenomic revolution via the HapMap and more widespread sequencing will make clear to many individuals that the focus on uniparental lineages over the past 15 years (NRY and mtDNA studies) has only illuminated half the story, and that the tale told by functional alleles is not necessarily going to be concordant. Additionally, I also believe that we are on the cusp of the age of morphological rengineering, when the very perception of "biological kinds" will be subborned by biotechnology, cybernetic augmentation and cosmetic resculpting.

But none of this means that pithy phraseology will go the way of the dodo. I am not satisfied with the phrase "phylogeny does not imply morphology" because "morphology" seems too narrow. On the other hand, phenotype seems clunkly. Any suggestions?

1 - I am well aware that this perception is sensitive to the choice of characters.