Do we need a better concept than species?

But the paleontological method would only reveal physical differences, not the gene pool isolation, correct? Like you could have two sexual life forms that looked alike but were actually separate species in the sense that they were unable to interbreed, but a fossil would not show that.(I've had two different definitions of species given to me on this forum. EZscience said that it meant that the two groups COULD not interbreed; others have said that it meant that the two groups DO not interbreed, not that they can't theoretically. According to the latter definition, if you had two groups of bears of the same type, one group in Oregon and the other in Vermont, then they would constitute two different species. That doesn't make sense to me.)

Correct, unless these were samples recent enough to allow recovery of some gentic material, as in the case of the neanderthal mtDNA sequences. Such sequences might not completely rule out gene flow, but they could be suggestive. Generally geographic isolation itself is not considered sufficient to classify different populations as seperate species. If the two populations are subsequently reintroduced to each other and can successfully interbreed then they would not be considered to be seperate species under the biological species concept.The distinction is more commonly drawn between pre-zygotic, i.e. behavioural or morphological, barriers to reproduction as opposed to post-zygotic, i.e. physiological or genetic or developmental, barriers to reprodcution leading to either a lack of interfertility or a lack of viability or sterility in hybrid offspring.TTFN,WK

I also agree entirely. It was the my uneasiness with the examples of observed 'speciation events' in real time, despite the highly slippery concept of species at that level of differentiation, that led me to delurk and make my first post here. Irreversible separation of gene pools will of course eventuallly occur given enough time, but 'event' seems totally inappropriate for such a long, drawn-out procedure.Cheers,SteveN

"speciation process" would make more sense as a term to me.

After digging my hands in the dirt for five years at an Allosaurus site, I've found it's pretty evident that the traditional definition of species as espoused by Mayr of discreet interbreeding populations is, well, impotent at fueling much worthwhile discussion in paleontology.Simply put, genotypes and phenotypes are not reliable measures of each other. Hopefully most of you out there are already familiar with this fact. However, I don't think that we can just cast aside the concept of species because then we've cut off our own legs, we have to have a fundamental unit to measure and test to gain any realistic data. Biologists can use contemporary populations, we in paleontology have a sparse random sample (arguable at that).Let me use an analagy of cats in their "kind" - haha. But, for the purposes of metaphor, imagine every Lion, Cheetah, Leapord, and Panther to be found in the fossil record to represent a time span of 2-3 million years in Africa. Now, put 150 million years worth of dirt on their graves along with some selective fossilization, with leapords fossilizing well due to their reliance on trees, often growing in riparian zones. Panthers... damn, those jungles are not good for fossilization, no excesse minerals to permineralize the bones! Cheetah's and Lions... they're grassland species, is their enough water flow to fossilize them?Anyway, you would have some 10 - 15 "complete" skeletons (i.e. 65 - 80% complete), and an assortment of scattered bits. Now, are they one species or several? How would you tell? The gracile cheetah could be confused with a lion becuase one could argue convincingly that they represent dimorphic patterns between males and females... which of course leads to assumptions about social life which would not reflect the actual relations of either species. Ultimately, their skeletons are so similar that the concept of species is problematic at best, and at worst downright misrepresentative and would result in a horribly re-contstructed ecosystem.So, the term "species" should not have the same meaning in different disciplines of science. Instead. let's measure exactly within the boundaries of our hypothesis. In the case of allosaurs (which has a more spotty fossilization record than the scenario above), the debate centers on if their are two species, A. fragilis and A. jimmadseni, or just one highly variable species of A. fragilis. To enter this debate, a hypothesis is formed that the convex margin of the jugal defines A. fragilis while a straightened one defines A. jimmadseni in conjuction with smaller body size... okay, I won't bore you with jargon. The end result is that the term "species" is defined in a way that functions to make the hypothesis testable.In much the same manner, the term "species" has a specific meaning in biology that also is testable in the context of genetics.Remember, the Linnaeus classification system of Kingdom, Phyla, Class, Order, Family, Genus, and Species came about before Darwin and Wallace's theory of evolution, which in turn came out before Mendel's work on genetics was made widely available. The concept of "Species" is unfotunately the apex of this trichotomy. But there is good news, a new classification system known as the Phylocode, already taught to many undergrads in bio 101, focuses more on larger groupings of organisms. Google it if you want more information on it (hey, since when did "google" become a verb?).Anyway, if you've read this far, the take-home message is that species is better used as a functional term in context of a specific research goal... anything out side of that is going to cause serious confusion of all "kinds".All the best,
Theus

English is a positional language, so basically, you can verb any noun. (oo, like I just did.)

Hi TheusThanks for your post. I actually hadn't put much thought into the (now obvious) problems in using the species definition in paleontology. 'Isolated gene pools' and 'ability to breed' are clearly useless for extinct species.Your following point.... ....while being perfectly reasonable for those working in their respective fields only helps to highlight how tenuous the species concept is 'in real life'.I've downloaded the pdf file of the PhyloCode current draft, which I will read in detail when I have time, but am I right in thinking that the phylocode is aimed at standardising the naming conventions? This would surely make everything a lot easier for people from a wide range of scientific investigation but doesn't seem to address the problem of defining a 'species' per se.I have this sort of fuzzy idea that if we could do a nice quick complete genomic sequencing of individual organisms we could talk in degrees of homology with other individual organisms rather than belonging to this or that species. I realise that in practical terms (both in the amount of sequencing involved and the horrendous complexities of phylogenetic analyses) this will probably remain a pipe-dream for quite some time. It's bad enough with HIV (my field) which only has about 10000 bases in it's genome.##Note added in edit##
I've just realised how stupid that last paragraph was. Obviously, an irreversible separation of gene pools could arise from a small number of mutations. Given the genetic variation amongst members of the same species, these mutations would be irrelevant without knowledge of their phenotypic effects. So much for that idea! I'm just glad that I managed to correct myself before somebody else did.
##End of edit##Cheers,SteveNThis message has been edited by SteveN, Sun, 07-08-2005 01:31 PM

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Simply put, genotypes and phenotypes are not reliable measures of each other. Hopefully most of you out there are already familiar with this fact.

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YES.

Crashfrog, that is quite possibly the coolest sentence I have ever read.

Yeah, the Phylocode is basically a constitution of species names. The first few articles (at http://www.ohiou.edu/phylocode/art1-3.html) go over the definitions, but essentially the names of species are not ranked, and the idea is looking at divergence. So...Wherease the Linnaean Classification system was like a high school prom, with member species ranked by category, superficial morphological characteristics and cheap tux rentals, the phylocode is more like the high school library, thoroughly indexed and put on shelves based on contents. The most problematic aspect may be with paleo species aha! Those 99.9% of life that came before us with no isolated genetic heritage but fortunately they can be defined by —gasp- traits we can measure with their closest relatives, which also happen to be extinct (if we're lucky... or if they're not lucky). Outside of that we’ll whip out the phylogenetic bracketing and ambiguous inference levels to make sense of their crazy, crazy world.There are a number of other provisions to the phylcode, in fact many numbers of other provisions, what is mentioned above is perhaps the most applicable to the current discussion. What disturbs me is how esoteric this sort of discussion is perhaps a thread should be dedicated to the reconciliation of paleontology and contemporary biology.שלום
Theus

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Veri Omni Veritas

Hi TheusI've been thinking about your posts and am somewhat mortified to realise that I, a professional biologist (albeit virology/immunology) and amateur 'evolutionist', have never given even a millisecond's thought to how extinct species are defined. If what you say is correct, there seems to be a fundamental difference between the approach to definitions in the extinct and extant camps. For extant populations, the biologist will take whatever definition of species applies to the organisms in question and will see whether the population fulfills that definition. If I understand you correctly, paleontologists first have to decide on a custom-made definition for a particular species. These are indeed two fundamentally different approaches and I think that your suggestion... ...would be a good idea. If you were to start one, I would read it with interest, although I could probably do little to contribute.Cheers,SteveNThis message has been edited by SteveN, Mon, 08-08-2005 04:51 PMThis message has been edited by SteveN, Mon, 08-08-2005 06:37 PM

Self-referential grammar is pretty awesome.

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suggestion...

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Theus writes:
..perhaps a thread should be dedicated to the reconciliation of paleontology and contemporary biology

...would be a good idea. If you were to start one, I would read it with interest, although I could probably do little to contribute.
Cheers,
SteveN

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I also found the much-hyped 'fight' between Gould and Dawkins concerning he role of PE in evolution to be a storm in a tea-cup. I may be totally wrong, but I seem to remember that Dawkins does not dispute the probability of long periods of stasis between periods of rapid evolution. He just thinks that this is obvious and disagrees with PE being promoted as a 'new' and important advance in our understanding of evolution.

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@I'm sorry if this doesn't address your points but to be honest, despite reading your post three or four times, I can't quite figure out what your points are.

Well to be bold I would point out that Gould brought down the "Berlin Wall" between the two sides in the thumbnail reprint of George C. Williams' ADAPTATION AND NATURAL SELECTION. The only way I can see that Dawkins would be correct that Gould's promotion of the motion on the largest scale of evolution is NOT "new", as you said, is if Richard and Stephen WERE NOT talking about the *same* population. But as it WAS, RDawkins thought it might be possible to get togehter with SGOULD in what I would signify as "clipping" if this was football and not an academic debate contra creationISTS (in book) thus from that writing I concluded that this IS the same 'population' less Mayr's full scientific criticism of PE stands and PE fails to be any important advance NO MATTER WHAT RELATIVE FREQUENCY consensus eventually assigns to the symbols that might be writ from it's alleged 'newness'. Now, you did not say that YOU, STEVEN did not justify that PE is not new you only wrote for RD etc. I will continue to write in the difference of biotic and organic "evolution" of Williams that hierarchical renaming in biology remands continually. And I am somewhat averse to Gould's newer position to restrict controversial discussion to the bottom of my seperated wall inverted and rotated version of Williams' figure TWO directly below.notice, as I do, that Gould's counting on PE can be visualized as the choice between the upper&lower concatenated figures BUT IT IS EQUALLY INTERESTING TO LINGUISTICALLY NOTICE THAT BARAMINS COULD BE DEFINED BY THE SAME LARGER PICTURE OF BOTH SUPERIMPOSED SHOULD SAY ORTHOGENESIS CAUSE THE EFFECT OF THE OVERLAY BY ORTHOSELECTIONS ORTHOGONAL TO WILLIAMS' POINTS THAT I HAVE SOMEWHAT FILLED IN.Now indeed this might not be 'new' if the SYTHESIS of adaptive units as furthered in the same discussion by DS Wilson in "Darwin's Cathedral" spoke of what appears in my figure as the Cambrian Explosion dewalled but then THEORECTICAL BIOLOGY would be what I expected it to have been when I wanted to become a mathematical biologist in the early 80s. Sadly it is not and we dispute the lengths of these points only in English and other languages. This message has been edited by Brad McFall, 08-16-2005 07:46 AM