Are species real? (re: hybrids)

Steve Manning sdmanning at ASUB.EDU
Wed Apr 12 09:39:36 CDT 2006


At 12:39 PM 4/11/2006 -1000, Richard Pyle wrote:
> > Part of that bias being that most cultures are not interested in defining
> > species as they are in nature (assuming that they are real), and part
> > being lack of technology necessary.  I doubt, for example, that many
> > people outside the current "culture of science" tried to separate the
> > species of scolytid beetles.
>
>Agreed on all points above.
>
> > Ah, but that's changing the rules of the game.  Species are real at any
> > one point in time (fortunately, evolutionary-scale time works for the most
> > part); beyond that, as you say, things get sketchy.
>
>The point is this: When you draw an arbitrary line through time (say,
>2006, or the 20th ceuntury, or the Holocene), that line will intersect
>some assembalges that seem unambiguously delineated from all other
>assemblages (e.g., Homo sapiens), and some assemblages for which there is
>a great deal of ambiguity about where species lines should be
>drawn.  Perhaps the frequency of the former is vastly greater than the
>frequency of the latter, in which case the latter can be written off as a
>minor "edge effect", a narrow "fuzzy" halo around a small number of cases
>in a context otherwise dominated by objectively discernable
>species.  However, from my perspective, in many groups it seems that
>abiguity is the norm.  That is, most groups are, if not dominated then at
>least non-trivially populated with, examples where reasonable lumpers and
>splitters will disagree as to whether we're looking at two sister species,
>or two geographic variations of the same species.

I sort of like to think of myself as a lumper in philosophy and a splitter
in practice.  In other words, in the usual situation where we don't have
data on interfertility between groups, I think it is probably preferable to
act on the presumption that if differences are consistent within the
specimens available (often only one or a few of each), they are different
species.  This is likely to result in more precise descriptions of the
observed variations and how they cluster together or don't.  Then, if later
experimentation/observation indicates interfertility between the two or
more separate species that were described, they should be combined.

But of course this again leads to the problem of quantification, and what
percent fertile hybridization either in nature or in controlled
environments should be enough to combine the species.  Most including
myself are reluctant to combine long-recognized speces (think of dogs and
coyotes) so don't do it despite interfertility.  Should standards be set,
in the ICBN or elsewhere, that a certain percent of successful
interbreedings as determined by peer-reviewed studies, require combining
previously separate species?  Or infertility between previously lumped
groups ("cryptic species") require the two to be split?  I can see merit to
this; as groups become better known, it might become a normal progression
for species in most groups to be combined and their status no longer an
argument between "lumpers" and "splitters" when their biology becomes
better known.  The diversity within the group would nevertheless have been
(hopefully) well described in the original "splitter" type species
descriptions.

Steve

>If the cut-and-dried, no-ambiguity cases are far and away the norm, then
>we can probably settle on a practical notion of "real" and think of
>species as being correctly or incorectly treated as different species;
>with only a few rare exceptions.  But I don't think that's the case -- I
>think a larger proportion of biodiversity (than most people realize) at
>any given cross-section of time falls into the "fuzzy" zone, such that
>what many may think of as the exceptions, actually end up being the
>rule.  If that's the case, then the notion of "real" has little place in
>conversations about where to deliniate species boundaries.
>
>Aloha,
>Rich

Dr. Steve Manning
Arkansas State University--Beebe
Mathematics and Science
Professor of Biology
P.O. Box 1000
Beebe, AR  72012
Phone: 501-882-8203
Fax: 501-882-4437




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