[Taxacom] [iczn-list] GENERAL CALL TO BATTLE

[John Grehan]

Hi Les,

Thanks for the elaboration. I am in some sympathy with your perspective.
After all, I spent (or misspent) more than 10 years ruining my reputation
(if not ruined already) by arguing for the morphologically based theory of
a human-orangutan clade. Got me nowhere of course. Agree that morphological
characters are more open to individual assessment whereas sequence
similarities have to be more or less taken on faith (and where many
homologies are created by alignment rather than having an actual real
existence).

The relationship between morphology (which is really morphogenetics) and
sequences is, as you intimate, challenging to say the least. When I see a
difference in the shape of a single feature in the genitalia of a moth, how
might that 'show up' in DNA sequences – whether any unique structural gene
or in some unique change to one or more regulatory genes. I doubt we will
ever know that until we reach the point where we can construct a designer
organism from scratch – directly from some base sequences and predict every
detail.

“On the other hand, a lot of genetic distinction of "species" is based on
mitochondrial genes, which have no relationship to morphology at all, and
may not vary in line with the nuclear genes that do.”

Yep – sometimes recognized as a difference between species trees and gene
trees, and how is one really to know which is what?

“I suppose that is my real trouble with using DNA sequences to define
species.”

Well, you are not alone in that. But if it's allowable under the code then
it is allowable even if others have trouble with that – just as I have
trouble with the purely sequence proposition that humans make a sister
group with chimpanzees.

“I am more comfortable with morphology, because I know that the morphology
I see must result from the expressions of a large number of genes.”

I might feel the same way, but ironically end up using molecular based
phylogenies for much of my biogeographic work as that is what there is to
use even if I may wonder about its veracity. Perhaps more critically is the
problem of relating DNA sequence defined living clades to morphologically
defined fossil clades. If only the former is 'reliable' when how can it be
related to the latter? One sees the potential absurdity with the earliest
unambiguous fossil hominids having orangutan rather than chimpanzee or
African ape features.

Lots of fun.

John Grehan