Mayr on "What is a Species"
pierre.deleporte at UNIV-RENNES1.FR
Tue Apr 27 11:39:41 CDT 2004
A 09:03 26/04/2004 -1000, Richard Pyle wrote:
>But if the "biological system" depends on some sort of cohesive
>inter-connectedness among "individuals" (sensu Deleporte), and you do not
>include the dead individuals as part of this system, then what, exactly, is
>it that establishes the interconnectedness? Wouldn't a "population", then,
>be restricted to simultaneously extant direct kin sets, or perhaps a flock
>of birds or school of fish, or other set of individuals that have direct
>"here-and-now" interconnectedness? When I think of the word "population", I
>infer a set of individuals joined by genetic heritage. And as such, I find
>it hard to think of a population without also including the dead ones.
Effectively, what we call "a given population" is possibly, and I would say
frequently, a very loosely biologically connected system between living
individuals. This is why I introduced "social group", and you introduce
But as Ron states himself clearly, the individual (just a bird in the hand)
is far more a cohesive biological system than any population, or part of.
All members of a poipulation, including dead ones if we include them in the
definition, can be said to share a property of effective or potential
interbreeding, as well as members of species. The notion of "effective or
potential" seems important to me in this discussion. The individuals
potentially reproducing together are not really reproducing with one
another. They share a property (reproducing compatibility), which we use as
a classificatory criterion. Such a species or population is a taxon, not a
real network of effectively interbreeding individuals. Just think of
completely separate populations of a "same species", and of course you can
have completely separate strains in a "same population".
If we quit just one second the anthropocentric view of considering sexual
species, and consider strictly clonal species, what is a population? In
this case, a population, and a species, become typologically defined taxa,
possibly with an additional geographic criterion for "population". They
cannot be defined as potentially interbreeding, but only as sharing a
common descent and looking like a given "type". A mutant judged
"significantly different" by the taxonomist is immediately the first member
of a new species.
This is, I think, the problem Kirk Fitzhugh unfortunately avoids dealing
with in his essay about species. I suggest that Kirk, and all of us, begin
with thinking of a species in non-sexual critters. Typology will impose
itself as the taxonomic (classificatory) criterion.
From this solid ground, extension to the more complexe figure of sexual
lineages will be possible, by trying to deal with the cross-breeding mess
in addition to (not instead of) the typological criterion. [Back to my pink
But if a species (lineage) is an "individual", then all life from the
origins up to now is an "individual"... who really buys this?
[Not to mention that, in classificatory logics, an individual cannot have
individuals as parts, while classes may have subclases as components, with
individuals composing only in the terminal classes... the notion of
"individuals as part of individuals" seems flawed to me - as well as to
Mahner and Bunge - anyway you take it, logically and ontologically... but
will I again be taxed of semantic games?...].
>I think I understand where you are coming from on this; taking a population
>to be some sort of "snap-shot" of a cohesive set of organisms that somehow
>comprise a biological system.
I mean "some" biological cohesion here and now. But you're right in your
>But the VAST majority of individuals within
>most sets of organisms that I would consider to constitute a "population"
>would never, in any way, interact with each other during the course of their
>lives. They are only joined, it seems to me, by their shared evolutionary
>I would agree is you were defining a single coral head as a "population" of
It's effectively a much more cohesive "population", because it involves
anatomo-physiological links, which define an individual organism. Nature
decidedly makes nothing to facilitate our urge for universal classifications!
>Geographically-defined populations are, in a way, potentially
>much less genetically cohesive than units we refer to as "species",
I can't follow you here, if populations are subclasses of a species they
cannot be more loosely defined given we use the same set of criteria. You
add at least spatial proximity for populations, and then in much cases
improved chances of local cross-breeding. But of course you can find or
imagine exceptions to the rule (nature is pitiless for classifiers).
>It seems we differ only in how we scope a "population". If I understand
>your definition/scope, I would tend to use words like "school", "herd",
>"flock", "colony", etc. to circumscribe a set of directly-interacting
You understand quite well. But I learnt with my professor of population
ecology that "a population is what you decide to define as a population
given the needs of your ongoing research". Classification again, allbeit
based on biologically relevant criteria. Populations are frequently defined
as loose systems, the loosiest being "mere geographic proximity".
> The word "population", to me, transcends the direct
>interactions among simultaneously extant individuals, and neccessarily
>includes the dead ones (and yet-to-be-born ones).
Under this definition, it's clearly a class ("taxonomic", Ron would say),
not a real biologically cohesive whole.
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