mesibov at SOUTHCOM.COM.AU
Sat Apr 17 09:10:44 CDT 2004
Ken Kinman wrote:
"When I look out the window at a robin, there is no doubt in my mind that it is
a real species, and that this robin is going to mate with another robin."
A lot is happening in Ken's mind here, but it's good he's given us a concrete
example. We see an individual robin and accept that it's real (and a
realistically separable bit of the continuum of existence) . If we watch long
enough we'll see it mate with another robin. The realities we're dealing with
are individuals and their breeding networks. Beyond those realities we're
hypothesising. We do it energetically and fervently, but we're still just
Ken: "I believe that the vast majority of speciations are mother species giving
rise to a daughter species, but this usually takes a very long time, and the
incipient daughter "semispecies" can be absorbed back into the mother
species given the right conditions. It is thus a judgment call whether full
speciation has occurred, and even then species can still interbreed under
That's why Wiley's 'evolutionary species' concept is so useful: 'A species is a
single lineage of ancestral descendant populations of organisms which
maintains its identity from other such lineages and which has its own
evolutionary tendencies and historical fate'. Since we can never be sure what
the historical fate of a particular lineage will be (it hasn't happened yet),
describing that lineage as a species, i.e. an evolutionary species, is always a
judgment call. It's an hypothesis, and explicitly so.
Ken: "I'm probably open[ing] more than one can of worms here, but what the
The biggest worm-can is the temporal one. It's been a long time since
biologists (as opposed to naturalists) saw Life typologically as a set of
discrete objects (species) which can be sorted into a classification, one to a
pigeon-hole. Since Darwin's time we've been seeing Life as a process.
Lineage throws off lineage through time. On a finer scale, each discrete
lineage is a braided stream. On an even finer scale, we're back to those nice,
solid individuals and their breeding networks. (This picture also works quite
nicely for gene histories.)
It's a worm-can because even though this is a dynamic picture, we usually
talk about it in non-dynamic terms. Unless your species concept is a
'Wileyian' one, your 'species' is a static snapshot of a cross-section of a flow.
How real is that? Similarly, a phylogenetic hypothesis is a static snapshot of a
side-on view of a flow. How real is that?
Maybe someday we'll talk about the flows as flows, maybe using terminology
borrowed from hydraulic engineers. We might even put a proper spatial
dimension into our talk; after all, every lineage split has (had) a location. But
even then, we'll be hypothesising. Is this a problem?
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery
Home address: PO Box 101, Penguin, Tasmania, Australia 7316
Home phone: (03) 6437 1195
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