[Taxacom] double-peaked mountains

[Richard Pyle]

>        However, when we are talking about genera, families, and higher
taxa,
> how many species we include in a given genus or family is defined (a human
> construct).  I am not saying that the lineage containing those species is
not
> real, since a group of real species would also be real.  So I guess what I
am
> saying is that species and their populations have a reality (often with
fuzzy
> boundaries) that is produced by nature, but how many species we include in
> a given genus or family is a defined human construct which is neither
fuzzy or
> real. Only the lineage containing that group of species is real.

I remain unconvinced that species are any different on the [real|fuzzy|human
construct] spectrum than higher taxa -- at least in terms of what I observe
as patterns in nature.

There is one thing that is fundamentally different between clusters of
organisms in the [kin|population|geographic
variant|subspecies|species|species complex] range, and the
[genus-and-higher-rank] range.  The fundamental difference is that, for the
former group, there is varying degrees of gene flow over time-scales ranging
from ecological to evolutionary.  But gene flow falls off to something
indistinguishable from zero once you get above the species/species-complex
level. (Acknowledging that inter-generic and inter-familial hybrids to
occur...)

It may well be that there is some sort of meaningful inflection point right
around the species level where patterns of divergence over time changes
fundamentally.  As such, one could argue that there are two fundamental
ranks of organism clusters: those that exchange genes at meaningful rates
over evolutionary timescales, and those that (effectively) do not exchange
genes at meaningful rates over evolutionary time scales.

Nevertheless, I don't see any difference in the relative "real-ness" of
clusters of organisms that we humans measure and define at these different
scales, because ultimately the "reality" is that many, many, many individual
organisms exist and reproduce over time, and their descendants differ to
degrees roughly in proportion to the generational distance between ancestor
and descendant. I have not seen evidence supporting some sort of
discontinuity in the pattern at or around where the gene-flow frequency
reaches an asymptote very near to zero.

Aloha,
Rich