sharp@hpfcdj.HP.COM (Darrin Sharp) (06/03/91)
Last night, on the "National Geographic Explorer", there was a segment on the coelocanth (sp?). This is a fish that was thought to be extinct, but live specimens were rediscovered in the 1930's off the S.E. coast of Africa. Since then, several are caught each year. The show made mention of the fact that these fish were unchanged for the last 400 million years. I know that outwardly, the live specimens very closely resemble the 400 million year old fossils. But how can this be? Is it common for organisms to not evolve for 400 million years? How long has it been since sharks and alligators/turtles/crocodiles evolved? Any other species that haven't changed in this long? Darrin Sharp (sharp@hpfcla.fc.hp.com)
wrp@biochsn.acc.Virginia.EDU (William R. Pearson) (06/04/91)
In article <17580003@hpfcdj.HP.COM> sharp@hpfcdj.HP.COM (Darrin Sharp) writes:
]
] Last night, on the "National Geographic Explorer",
] there was a segment on the coelocanth (sp?). This
] is a fish that was thought to be extinct, but live
] specimens were rediscovered in the 1930's off the
] S.E. coast of Africa. Since then, several are
] caught each year.
]
] The show made mention of the fact that these fish
] were unchanged for the last 400 million years.
]
] I know that outwardly, the live specimens very closely
] resemble the 400 million year old fossils. But how
] can this be? Is it common for organisms to not evolve
] for 400 million years? How long has it been since sharks
] and alligators/turtles/crocodiles evolved? Any other
] species that haven't changed in this long?
]
] Darrin Sharp (sharp@hpfcla.fc.hp.com)
This claim is frequently made about animals that physically
resemble ancient ancestors. It is, of course, false. There are many
examples of "primitive" organisms that exist in an "unchanged" state.
At the molecular level, their enzymes and DNA have diverged at the same
rate as "modern" animals. If an organism is living today, it is "modern,"
regardless of how it looks.
Bill Pearsonvamg6792@uxa.cso.uiuc.edu (Vincent A Mazzarella) (06/04/91)
> This claim is frequently made about animals that physically >resemble ancient ancestors. It is, of course, false. There are many >examples of "primitive" organisms that exist in an "unchanged" state. >At the molecular level, their enzymes and DNA have diverged at the same >rate as "modern" animals. If an organism is living today, it is "modern," >regardless of how it looks. But, of course, genomes of every human is quite different from every other human. What matters are those differences causing a change in phenotype. While the genome of a coelocanth has changed over the millenia, it is noted that the meaningful changes, those that cause phenotypic changes, have been few. The way you present "primitive" and "modern" is pretty much semantics and an absolutist, old metaphysical philosophy. -- Vincent Mazzarella College of Medicine, Neuroscience Program University of Illinois, Urbana-Champaign e-mail: mazz@vmd.cso.uiuc.edu
christo@psych.toronto.edu (Christopher Green) (06/04/91)
In article <17580003@hpfcdj.HP.COM> sharp@hpfcdj.HP.COM (Darrin Sharp) writes: > > Last night, on the "National Geographic Explorer", > there was a segment on the coelocanth (sp?). [...] > The show made mention of the fact that these fish > were unchanged for the last 400 million years. [...] > How can this be? Is it common for organisms to not evolve > for 400 million years? How long has it been since sharks > and alligators/turtles/crocodiles evolved? Any other > species that haven't changed in this long? Read up on punctuated equilibrium. Niles Eldridge's _Time_Frames_ is a good popular account. The more technical stuff can be found in _Dynamics_ _of_Macroevolutionary_Theory_ (or something close to that). Great stuff! Have fun! -- Christopher D. Green Psychology Department e-mail: University of Toronto christo@psych.toronto.edu Toronto, Ontario M5S 1A1 cgreen@lake.scar.utoronto.ca
sarima@tdatirv.UUCP (Stanley Friesen) (06/05/91)
In article <17580003@hpfcdj.HP.COM> sharp@hpfcdj.HP.COM (Darrin Sharp) writes: > Last night, on the "National Geographic Explorer", > there was a segment on the coelocanth (sp?). This > is a fish that was thought to be extinct, but live > specimens were rediscovered in the 1930's off the > S.E. coast of Africa. Since then, several are > caught each year. Sigh, I would have hoped NGE would get this right. The coelacanth is a species in a *group* of fish that was thought to be extinct. The living species of coelacanth was completely unknown prior to its discovery in the '30's. It closest known relatives are fossils from many millions of years ago. There are not even any fairly recent fossil relatives. Thus, in the absence of any 'recent' fossils or any known recent species the whole group was assumed to be extinct. > The show made mention of the fact that these fish > were unchanged for the last 400 million years. Bull****! They are *little* changed, having essentially the same anatomy as their 400 MY old relatives. But in many details, some of them significant, they have changed considerably. It is easy for even a non-biologist to tell the difference between the coelacanth and it closest (400 MY old) relative. They *look* different. [About as different as a goldfish and a river carp]. > I know that outwardly, the live specimens very closely > resemble the 400 million year old fossils. But how > can this be? Is it common for organisms to not evolve > for 400 million years? How long has it been since sharks > and alligators/turtles/crocodiles evolved? Any other > species that haven't changed in this long? *No* species are unchanged for this long. NGE was wrong. The earliest sharks probably predate the lobe-fin fishes (the group to which the coelacanth belongs). They were, however, quite different than modern sharks. Sharks of more or less modern aspect appeared very early though, perhaps about the same time as the earliest lobe-fins. And the modern sharks are about as similar to these early sharks as the living coelacanth is to its early relatives. Crocodiles of more or less modern form appeared about 150 MY ago (give or take 20 MY). Except for size these would be almost indistinguishable from modern forms (except to an expert). The earliest crocodiles appeared about 220 MY ago. But these forms were very different, and I think even a layperson could tell them from modern crocs. (Alligators are, to a biologist, essentially just specialized crocodiles). Turtles are, for land animals, very ancient. The lineage may go back as far as 300 MY with almost no change in basic anatomy. (I am unsure of the dates here, I have not studied turtles in any depth). -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
abbott@ecsvax.uncecs.edu (John P. Abbott) (06/05/91)
More coelocanth. Short article in _New Scientist_, May 25, 1991, p13 (vol.130 no. 1770). "Hunt is on for the last of the "fossil" fish", Sue Armstrong.
kliman@mbcl.rutgers.edu (06/06/91)
In article <18@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: > In article <17580003@hpfcdj.HP.COM> sharp@hpfcdj.HP.COM (Darrin Sharp) writes: >> I know that outwardly, the live specimens very closely >> resemble the 400 million year old fossils. But how >> can this be? Is it common for organisms to not evolve >> for 400 million years? How long has it been since sharks >> and alligators/turtles/crocodiles evolved? Any other >> species that haven't changed in this long? > *No* species are unchanged for this long. NGE was wrong. This is clearly a question of semantics. As far as I know, there is no rule that phenotypic change must occur within some specified period of time (e.g., 400 MY). That is not to say that such change has not occurred in the coelocanth. However, there are far too many organisms yet to be discovered to categorically state that phenotypic stasis does not occur. Genotypic change is a different story - it should occur at whatever the neutral mutation rate is for every given region of the genome, if all of the rules of neutral evolution are obeyed. So by this definition of "change," even organisms with no clear phenotypic change over time are evolving at the nucleotide level. Still, it seems to me that there must be plenty of cases out there of organisms resembling, at a morphological level, their far distant ancestors; natural selection can favor ancient phenotypes if they remain superior, thereby overwhelming the force of mutation. Why not? - Rich Kliman
barger@aristotle.ils.nwu.edu (Jorn Barger) (06/06/91)
christo@psych.toronto.edu (Christopher Green) writes: > Read up on punctuated equilibrium. Niles Eldridge's _Time_Frames_ is > a good popular account. The more technical stuff can be found in _Dynamics_ > _of_Macroevolutionary_Theory_ (or something close to that). Great stuff! > Have fun! I'm a bit disappointed that only one coelocanth-followup mentions this obvious-but-still-apparently-under-disseminated viewpoint. This is hot stuff indeed, and theoretically revolutionary. The argument is that the classic pattern of evolution is not a smooth, gradual blurring from one species to another, but an alternation of relative quiescence and relatively rapid phenotypic transformation. I'll take this opportunity to present again my best guess as to the mechanism at work here: What has to be explained is why there may be adaptive mutations present in a genepool, _that don't spread through the entire population_. What is the conservative principle balancing natural selection? I claim it is sexual selection. If an ideal sexual stereotype is set up early on in the evolution of a new species, as it must be, then it may serve to reduce the sexual attractiveness of new adaptations that deviate from that stereotype. Perhaps a wide range of favorable adaptations can build up at the fringes of the genepool, in marginal niches where a slight adaptive superiority counts for more than sex-appeal, but never spread through the rest of the population, breaking through instead only when a change in the environment makes the niche marginal for the entire population. (Bonus question: what B-movie title is a fitting summary of this view?)
vamg6792@uxa.cso.uiuc.edu (Vincent A Mazzarella) (06/06/91)
What the Nat'l Geographic program failed to relay was the fact that the behaviour of the coelecanth has changed. While the intrepid scientists showed that the fish stands on its head presumably like an antenna detecting distant delectable dipoles, this has not always been its behaviour. Apparently, the ability to detect food by weak dipoles has actually diminished in this ancient fish, since cargo ships in the vicinity have lost microwave ovens in the seas around the Camorro islands. The fish, in an almost unheard of use of tools, now relies on microwave cooking for meals. Had the submarines tailing these ancient-like fish been able to follow them into their crevices, they would have seen the remains of many TV dinners, much like those of many who watch these documentaries. -- Vincent Mazzarella College of Medicine, Neuroscience Program University of Illinois, Urbana-Champaign e-mail: mazz@vmd.cso.uiuc.edu
sarima@tdatirv.UUCP (Stanley Friesen) (06/07/91)
In article <471.284d6041@mbcl.rutgers.edu> kliman@mbcl.rutgers.edu writes: >In article <18@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: >> *No* species are unchanged for this long. NGE was wrong. > >This is clearly a question of semantics. As far as I know, there is no rule >that phenotypic change must occur within some specified period of time (e.g., >400 MY). Perhaps so. But there is no known living *species* that is more than a few million years old (certainly no more than 10 MY). And *most* living species are around one million years old (or even younger). I would require truly impressive evidence before I would accept a claim that a *species* was anything like 400 MY old. Even genera almost never survive *that* long. (In fact I believe that the living coelacanth is in a genus different from all of the extinct forms). (Hmm, come to think of it I know of *no* genus that has lasted 400 MY years - I am not even certain if any *family* of sharks or turtles is that old - though one of the families of agnathans may be that old). >Still, it seems to me that there must be plenty of cases out there of organisms >resembling, at a morphological level, their far distant ancestors; natural >selection can favor ancient phenotypes if they remain superior, thereby >overwhelming the force of mutation. Why not? Quite true. But none are so closely identical (even morphologically) as to be considered to be the same species. Why this is so is, perhaps, a problem worth studying, but it is nonetheless true (by observation). My guess would be that no environment has remained sufficiently unchanged for more than a few million years for identical phenotypes to continue to be advantageous. The least changed forms I know of are probably crocodiles, but even they are detectably different. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
arlin@ac.dal.ca (06/07/91)
In article <17580003@hpfcdj.HP.COM>, sharp@hpfcdj.HP.COM (Darrin Sharp) writes: > > Last night, on the "National Geographic Explorer", > there was a segment on the coelocanth (sp?). This > is a fish that was thought to be extinct, but live > specimens were rediscovered in the 1930's off the > S.E. coast of Africa. Since then, several are > caught each year. > > The show made mention of the fact that these fish > were unchanged for the last 400 million years. > > I know that outwardly, the live specimens very closely > resemble the 400 million year old fossils. But how > can this be? Is it common for organisms to not evolve > for 400 million years? How long has it been since sharks > and alligators/turtles/crocodiles evolved? Any other > species that haven't changed in this long? > > Darrin Sharp (sharp@hpfcla.fc.hp.com) Previous respondents have made rigid statements, and I hope they haven't discouraged you. As several people have pointed out, it is a bit odd to speak of a "living fossil," and it is quite true that all extant species are "modern" in the sense of living in the present and being the product of the last 4.6 billion years of evolution. However, the respondents misunderstand the word "primitive." Also, to insist that there is no such thing as a living fossil and that all organisms evolve at the molecular level is to miss the point, since it does absolutely nothing to explain why the coelocanth (if that is how one spells it-- I forget) and other primitive species have undergone less apparent morphological change than one might expect. "Primitive" may be a value judgement sometimes-- when used in reference to professional hockey, for example-- but in evolution it can have a precise meaning, when used carefully. Any two species will have had a common ancestor at some time in the past: the species that is more similar to the ancestor is more primitive, in the exact sense. Usually, it is misleading to talk about whole organisms-- much better to speak of component properties. The ancestor of humans and whales walked on land. The terrestrial habit of humans can thus be considered primitive in comparison to the whale's marine habit. One can think of E. coli (as opposed to H. sapiens) as primitive in that it is unicellular, however, many features of this bacterium are probably not primitive. Thus, it is easy to use the word "primitive" in an exact and objective way, provided that one actually knows something about the relevant ancestor (this is often difficult). The coelocanth looks alot like some 400 MY-old fossils, and that is why people can correctly call it primitive. To be precise, its gross morphology is primitive: note that 1) as one respondent pointed out, no one can tell about the details of external or internal morphology; and 2) as many respondents pointed out, this apparent morphological primitiveness does not imply molecular primitiveness. There is good reason to expect that coelocanth molecules have been diverging from the ancestral type just as do those of other organisms. The Port Jackson Shark is another morphologically primitive species: it has a morphology similar to that of some sharks from the Carboniferous period (ca. 300 MYA). When the hemoglobin proteins of this shark were sequenced over 15 years ago (Fisher, et al., Aust. J. Biol. Sci. 30: 487), it was made clear that molecular evolution in the shark is proceeding at a rate similar to that seen in other organisms, even though the gross morphology of the shark changes very slowly. A similar result has been obtained for the case of the opossum, another organism whose morphology has remained substantially unchanged for a long time, in this case for roughly 150 MY (see Stenzel, Nature 252: 62). So . . . many respondents have corrected the way you stated your question ("is it common for species to not evolve?") by pointing out, as I have, that every organism is expected to evolve at the molecular level, regardless of the rate of evolution at the morphological level. But this doesn't answer the intent of your question, does it? Its exciting to think of primitive organisms and to imagine that they are a window to an otherwise murky past: you want to know why the coelocanth appears to live the same way for 400 MY while other organisms diverge from their ancestors and quickly acquire new properties! There is presently no good answer to this question, as far as I know. One possibility is that a) these organisms have simply achieved a morphology that is well suited to their lifestyle *and* b) their niche has remained stable for long periods of time, so that there is no pressure to change. Meanwhile, other species diverge from the primitive type, as they a) continue to improve on their body plan and/or b) change to keep up with the times. There are other possible explanations. Arlin Stoltzfus, Department of Biochemistry, Dalhousie University Arlin@ac.dal.ca
kliman@mbcl.rutgers.edu (06/09/91)
In article <29@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: > In article <471.284d6041@mbcl.rutgers.edu> kliman@mbcl.rutgers.edu writes: >>In article <18@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: >>> *No* species are unchanged for this long. NGE was wrong. >> >>This is clearly a question of semantics. As far as I know, there is no rule >>that phenotypic change must occur within some specified period of time (e.g., >>400 MY). > > Perhaps so. But there is no known living *species* that is more than a few > million years old (certainly no more than 10 MY). And *most* living species > are around one million years old (or even younger). > > I would require truly impressive evidence before I would accept a claim > that a *species* was anything like 400 MY old. Even genera almost never > survive *that* long. What is the definition of species here? Certainly bifurcations have occurred in the phylogenies of all extant species. However, does this cause the extinction of the ancestral species? I don't think we can determine if any extant species can produce fertile offspring in a cross with some distant ancestor (if we use that particular definition of species), so to say that no species is more than 10 MY old is just an assumption. I'm not saying that the coelocanth is morphologically identical to its ancestor 400 MY back, or that it is even the same biological species. However, I stick to my prediction that *some* species (not necessarily a chordate) has not changed substantially for 400 MY. That is not to say that diversification through offshoot lineages (e.g., by "founder effect") has not occurred. >>Still, it seems to me that there must be plenty of cases out there of organisms >>resembling, at a morphological level, their far distant ancestors; natural >>selection can favor ancient phenotypes if they remain superior, thereby >>overwhelming the force of mutation. Why not? > Quite true. But none are so closely identical (even morphologically) as to > be considered to be the same species. Why this is so is, perhaps, > a problem worth studying, but it is nonetheless true (by observation). > > My guess would be that no environment has remained sufficiently unchanged > for more than a few million years for identical phenotypes to continue > to be advantageous. The least changed forms I know of are probably > crocodiles, but even they are detectably different. What I'm saying is purely hypothetical. I'm inclined to agree that all extant chordates probably differ from their ancestors from 400 MY. All I originally wanted to convey was disagreement with a statement that I considered too rigid. We simply don't know what the phylogenies of all living species look like, and all "rules" are bound to be broken occasionally. - Rich Kliman
squirrel@behind.caltech.edu (Patricia M. White) (06/10/91)
It seems to me that the term "primitive" is misleading to some people. A species that is considered ancient or primitive is an animal that is superbly adapted or adaptable. The opossum develops to adulthood quickly, can eat anything, produces many young, but dies after three years: it survives as a species without overpopulating its niche. Thus the opossum has been around for a long time. Don't think of it as "primitive." Think of it as doing something right. Pat White squirrel@above.ugcs.caltech.edu
mroussel@alchemy.chem.utoronto.ca (Marc Roussel) (06/11/91)
In article <676362297.46@egsgate.FidoNet.Org> Vincent.A.Mazzarella@f98.n250.z1.FidoNet.Org (Vincent A Mazzarella) writes: > > >> This claim is frequently made about animals that physically >>resemble ancient ancestors. It is, of course, false. [...] >>At the molecular level, their enzymes and DNA have diverged at the same >>rate as "modern" animals. If an organism is living today, it is "modern," >>regardless of how it looks. > >But, of course, genomes of every human is quite different from every other >human. I don't think this is true. Could a molecular biologist comment on this? I seem to remember that the amount of DNA that distinguishes you from me (or indeed that distinguishes me from a chimpanzee) is quite small. >While the genome of a coelocanth has changed over the millenia, it is >noted that the meaningful changes, those that cause phenotypic changes, >have been few. How do you know? You're not defining phenotype merely be external morphology are you? Marc R. Roussel mroussel@alchemy.chem.utoronto.ca
sarima@tdatirv.UUCP (Stanley Friesen) (06/12/91)
In article <472.28511bf9@mbcl.rutgers.edu> kliman@mbcl.rutgers.edu writes: >In article <29@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: >> Perhaps so. But there is no known living *species* that is more than a few >> million years old (certainly no more than 10 MY). ... >What is the definition of species here? Certainly bifurcations have occurred >in the phylogenies of all extant species. However, does this cause the >extinction of the ancestral species? Well, if you use the cladist's definition of species - YES :-| However, that is *not* the definition I was using. > I don't think we can determine if any >extant species can produce fertile offspring in a cross with some distant >ancestor (if we use that particular definition of species), so to say that no >species is more than 10 MY old is just an assumption. True, but that is not even sufficient evidence for living forms. Inability to cross-breed almost proves a species distinction, but ability to interbreed does *not* prove that two forms are the same species. The basic definition of species for living forms is that they do not *normally* interbreed successfully. This can be because they are too different in ecology, or mating habits for the adults to ever mate in the wild; or it could be that they are too different in lifestyle or morphology for the offspring to survive in the wild. With extinct forms you basicly have to *guess* whether this criterion holds. It is, of course, not as certain as with living forms, but it appears to work better than might be expected. (Of course its hard to tell!) > I'm not saying that >the coelocanth is morphologically identical to its ancestor 400 MY back, or >that it is even the same biological species. However, I stick to my >prediction that *some* species (not necessarily a chordate) has not changed >substantially for 400 MY. That is not to say that diversification through >offshoot lineages (e.g., by "founder effect") has not occurred. I do not believe this is likely. I suspect that any form would have changed enough in that amount of time that offspring would either never occur or fail to survive. The closest I have yet seen to this kind of constancy in known fossils is in the genus Lingula. (Which I had forgotten about in my previous postings). A case might be made here that living Lingula is close enough in morphology to one of the Paleozoic Lingula's to be considered the same species (but I stll doubt it - Lingula's have changed somewhat, and the differences seem to exceed the level typical for distinct species of brachiopods). [P.S. this is the practical criterion for fossil species - morphological differences exceeding typical within-species variation among living relatives]. >> Quite true. But none are so closely identical (even morphologically) as to >> be considered to be the same species. Why this is so is, perhaps, >> a problem worth studying, but it is nonetheless true (by observation). >What I'm saying is purely hypothetical. I'm inclined to agree that all extant >chordates probably differ from their ancestors from 400 MY. All I originally >wanted to convey was disagreement with a statement that I considered too >rigid. We simply don't know what the phylogenies of all living species look >like, and all "rules" are bound to be broken occasionally. Hmm, well, I wouldn't exactly call it a 'rule', more like a generalization from observation. The longest spans known for individual morpho-species are on the order of 10 million years, so on statistical grounds, I reject the likelyhood of a species so *far* out on the tail of the distribution. [Typical species last about 1 million years or so]. Certainly it is strictly speaking *possible* that a form remains so stable in all aspects of its biology as to remain viable with its ancestors for many milions of years, but it is *very* unlikely (P << .01). [In math the symbol '<<' means 'much less than']. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
kliman@mbcl.rutgers.edu (06/13/91)
In article <34@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: > In article <472.28511bf9@mbcl.rutgers.edu> kliman@mbcl.rutgers.edu writes: >>In article <29@tdatirv.UUCP>, sarima@tdatirv.UUCP (Stanley Friesen) writes: >>What I'm saying is purely hypothetical. I'm inclined to agree that all extant >>chordates probably differ from their ancestors from 400 MY. All I originally >>wanted to convey was disagreement with a statement that I considered too >>rigid. We simply don't know what the phylogenies of all living species look >>like, and all "rules" are bound to be broken occasionally. > Hmm, well, I wouldn't exactly call it a 'rule', more like a generalization > from observation. The longest spans known for individual morpho-species > are on the order of 10 million years, so on statistical grounds, I reject > the likelyhood of a species so *far* out on the tail of the distribution. > [Typical species last about 1 million years or so]. > > Certainly it is strictly speaking *possible* that a form remains so > stable in all aspects of its biology as to remain viable with its > ancestors for many milions of years, but it is *very* unlikely (P << .01). > [In math the symbol '<<' means 'much less than']. Okay. I was simply trying to make a point. But let's play with the numbers. If we assume there are only 1 million extant species, and if we make the assumption that the likelihood of a species being 400 MY old is .000001 (which I hope satisfies the criterion of P<<.01), then the probability that *no* species is that old is 38%. If there are 5 million species, the probability becomes .7% (i.e., 99.3% probability that some species is 400 MY old). If we change .000001 to .00001, then the probability that 1 million species are all recent is .0000454. Admittedly, I have made up these probabilities. I don't know what the value should actually be. Without the frequency distribution of known species, I can't estimate the value. If you know of a good source, I'd like to take a look. To the point: do I believe that some species is 400 MY old? I'm not sure. There's just not enough data to make an informed conclusion. With all of those plants, animals, protists, prokaryotes.... who knows. Perhaps some regions of the planet remain stable for eons, e.g., deep in the oceans. Maybe there's no stability, but particular environments move about slowly enough for adapted species to move along with them. How many different extant species are there, anyway? (Probably a lot more than 5 million). So what if the coelocanth isn't 400 MY old. Or any vertebrate, or any terrestrial animal (probably). The original question posed - can a species remain unchanged for that long - is fun to think about. I think it's possible, but if the author of the question wanted a definitive answer, he won't get one from this devil's advocate. - Rich Kliman
minsky@media-lab.media.mit.edu (Marvin Minsky) (06/14/91)
kliman@mbcl.rutgers.edu remarked,
>The original question posed - can a species remain unchanged for
that long - is fun to think about.
Consider that all we know about those "living fossils" is that their
external appearance hasn't changed very grossly. However, a good
proportion of the genome goes into the brain structure and
connections -- and we cannot see much of that. Now it seems to me
that there is a nice opposition here: any gross skeletomuscular change
has a central nervous price, because the reflex systems and higher
level instincts need reprogramming. (That is, to the extent that the
local learning systems cannot easily adapt.) And conversely, the less
superficial change, the easier to evolve new behavioral adaptations.
So, to first order, the more the Coelocanth seems the same -- outside
-- the more different it would be -- inside!
Of course, that wouldn't be true to second order. Because new
behavioral abilities brings with it new possibilities for changing