[Taxacom] Semantic Web: What is a species?

Richard Pyle deepreef at bishopmuseum.org
Sun Jan 25 06:15:13 CST 2009


I find myself nodding in agreement a lot while reading Ken's post on this. I
guess I would say that what makes species seem more "real", is that we
generally try to draw those lines at the inflection between near-seamless
reproduction, and non-reproduction.  In the genus/family/etc. range,
gene-flow is very easily characterized as hybridization.  In the
subspecies/population realm, patterns of gene flow are more easily
characterized as "population structure". The stuff in-between these two
realms is where the species fall.

Returning to my trusty example, there are some pretty damn good reproductive
barriers between myself and the palm tree in my front yard.  Yet we share a
common anscestor somewhere back there in time. Which means that at some
point in our respective ancestries, there was a time when it might not have
been so clear whether there was one species, or two.  In the case of humans
and palm trees, if we define time "A" as the first hint of divergence within
what was our single common ancestor, time "B" as the moment when the last
reproductive event occurred between our respective diverged ancestors, and
time "C" as now, then the timeline A-B is VASTLY smaller than the timeline
B-C. However, when we fall into the realm described above (i.e., the
"species zone") then the timeline ratios are not so lop-sided. The reason we
have "lumpers" and "splitters" is a consequence of the arbitrary nature of
where we perceive the "inflection" alluded to above. 

I think it's simply a general pattern that the farther down the scale we go,
the more real it appears to us.  Species seem more real than genera or
families. Populations seem more "real" to me than species.  Individual
organisms seem more "real" to me than populations. Individual cells seem
more "real" to me than individual organisms. Molecules seem more real to me
than cells. Atoms seem more real to me than molecules...and so on.

Indeed, I think your oxygen molecule analogy is better than you give it
credit for.  I think there are many, many examples of things that even a
lumper would call distinct species today, but which have the capacity to
converge at some point in the future. Does that mean they aren't "real"
species today? Or, are they multiple "real" species today, which simply come
together to form a single "real" species later?  

I agree with you that the group one works on colors one's perspective.  But
I'd bet that fishes are a whole lot more like terrestrial vertebrates than,
say corals and plants (which make fish species look extraordinarily "real"
by comparison).

Aloha,
Rich

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu 
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of 
> Kenneth Kinman
> Sent: Saturday, January 24, 2009 6:22 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] Semantic Web: What is a species?
> 
> Hi Pete,
>         I don't think you can generalize by saying that 
> taxonomists have a particular view of the reality of species. 
>  I am a taxonomist, not an ecologist (or other specialized 
> user of taxonomy).  Yet I agree with you that species are 
> more real than subspecies, genera, or families.
>        I certainly understand Richard's view that species are 
> also human constructs, but I think that they have an 
> evolutionary cohesiveness that makes them more "real" than 
> other taxa.  They certainly can have fuzzy boundaries 
> (especially when they have just split from another species), 
> and I think that is why I tend to lump more than I split.  
> When they are close to that speciation event (on one side or 
> the other), it is very difficult for us humans to know if 
> they have really crossed that line
> for good.      
>        In fact, it can't be known with absolute certainty 
> because we have no knowledge of future events (contingencies) 
> that could either push these marginal cases completely over 
> the species threshold or force them back together where gene 
> flow resumes to a significant degree.  I think polar bears 
> are a great example of this.  They clearly evolved from brown 
> bears, but we just don't know whether there will be any 
> significant resumption of gene flow as their breeding areas 
> are forced to overlap more and more.  
>       I really like to think of species that are close to 
> splitting as being sort of like two oxygen atoms in an 
> excited oxygen molecule.  They still share those outer 
> electrons that bind them together (= gene flow), but 
> something eventually comes along that finally breaks those bonds.
> It's not a perfect analogy, because real species usually 
> don't come back together after a certain point (whereas 
> oxygen atoms could do so more easily), but it should give one 
> an idea what I am getting at.  Anyway, that is my two cents worth.
>          -------Cheers,
>                         Ken Kinman                 
> P.S.  I think one reason that Richard and I see it somewhat 
> differently might be because I study land animals and he 
> studies fish.  I think that fish species in the ocean 
> generally have a little more fuzziness to them, and that it 
> is perhaps a bit harder for barriers to develop that force 
> one species to develop into two. 
> 
> 
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