[Taxacom] On genera, splitting and ranking

Chris Thompson xelaalex at cox.net
Sat Jul 13 12:46:46 CDT 2013


Ken:

As for the genus Homo, tell me what you believe the oldest fossil indication 
of this group is.

Then tell me why it is useful to maintain this as a "genus," when there are 
currently accepted genera millions of years older, such as Drosophila.

Yes, Kim:

Smaller organisms can have many more generations within the same time span.

But what we are looking for is a SCIENTIFIC, consistent, measure 
(yard-stick) with which to compare things.

So, one could say perhaps that the species in the genus Mus (mice) do in 
fact breed more frequently than those in the genus Homo (humans, etc.) do, 
but given that these "genera" represents the same amount of time (same age 
of origin, etc.), then that becomes a useful hypothesis to further 
investigate, such as why? More offspring or is investment in few offspring a 
better strategy for success?

Today, unfortunately as there is no scientific basis for ranking, we can not 
make any kind of scientific hypotheses about evolution or anything else on 
the basis of taxonomic units.

Ask the question of why there is some 2000 species in the genus Drosophila 
and less than a dozen (or less, depending on how one counts fossils, etc.) 
in the genus Homo, one can not say except that the definition of these 
genera are completely different and are merely subjective.

Yes, Ernst Mayr responded to Hennig by saying that ranking should reflect 
"anagensis," not "cladogensis," etc. And therefore, it was proper to put Man 
(Homo sapiens) in its own genus, family, order, etc., while Drosophila 
melanogaster was place merely as one of hundred of species of fruit flies. 
Obviously, man deserves special treatment given how far he has advanced over 
all other life, etc. The only problem with this "anagenetic" approach is 
defining a consistent unbiased measure of evolutionary "improvement," etc.

Sorry, but Hennig was right in linking rank of categories to age of origin. 
That proposal if it has been implemented would have given a minimal 
scientific basis for higher categories.

And these initial responses reveal what Hennig correctly realized a 
half-century ago, that is, there is NO science in taxonomic classification, 
and NO one will accept changing that.

Oh, well ...

Chris

from home

-----Original Message----- 
From: Kim van der Linde
Sent: Saturday, July 13, 2013 1:05 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] On genera, splitting and ranking

I think age is a useless criterion, because it assumes two things:

1. Age == evolution
2. Same age == same number of generations

Obviously, a shorter generation time implies more generations and thus
more genetic change. Evolution and change depends not only in the number
of generations, but also on the need to adapt to novel situations,
bottlenecks, and a load of other mechanisms that affect the realized change.

I think that what we are doing now is mostly perfectly fine.

Kim


On 7/13/2013 10:38 AM, Frank.Krell at dmns.org wrote:
> "Yes, Hennig once did propose a testable criterion for rank, that is, age 
> of origin. However, everyone, including Hennig himself, rejected that 
> criterion."
>
> Chris, would you remind me where he did so? I just cannot remember that he 
> did, but it is long ago that I read all his theoretical works (in German).
>
> "Age is a wonderful and scientific criterion for rank. If we had such, 
> then we could easily propose that higher Diptera (Cyclorrhapha, a 
> suborder) is the same as birds (Aves, a Class) and far more diverse [Yes, 
> the little creatures with narrow specialization generate more species, 
> than larger more generalized predators, etc.]. But these kinds of 
> scientific questions are not now possible due to the distorted system of 
> classification we have and used."
>
> Isn't it amazing that a clear and useful criterion, probably the only 
> phylogenetically justifiable criterion to define rank meets with so much 
> resistance, rendering comparisons beyond one's small research domain so 
> difficult?
> Tradition (Aves is a class, Scarabaeidae is a family) is so much more 
> important for emotionally heavily invested scientists than scientific 
> reasoning.
>
> And, of course, we have many paraphyletic species, but we should not have 
> paraphyletic higher taxa. There is no reason to let the pendulum swing 
> back to pre-hennigian times.
>
> Frank
>
> Dr. Frank-T. Krell
> Curator of Entomology
> Commissioner, International Commission on Zoological Nomenclature
> Chair, ICZN ZooBank Committee
> Department of Zoology
> Denver Museum of Nature & Science
> 2001 Colorado Boulevard
> Denver, CO 80205-5798 USA
> Frank.Krell at dmns.org
> Phone: (+1) (303) 370-8244
> Fax: (+1) (303) 331-6492
> http://www.dmns.org/science/museum-scientists/frank-krell
> lab page: http://www.dmns.org/krell-lab
> The Denver Museum of Nature & Science aspires to create a community of 
> critical thinkers who understand the lessons of the past and act as 
> responsible stewards of the future.
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