Scott Faust Speciation Hi, Wes. Have recently been posting a somewhat edited down version

Master Index Current Directory Index Go to SkepticTank Go to Human Rights activist Keith Henson Go to Scientology cult

Skeptic Tank!

Scott Faust Speciation Hi, Wes. Have recently been posting a somewhat edited down version of the speciation file on your BBS to good effect in several forums. ("Good effect" thus far seems to mean that the creationists try to ignore me .) I also wrote my own post with some additional examples of speciation that I have posted along with with your file in the DEBATE echo. Thought I would share that here: STEVE BEDARD to SIMON EWINS, 05-19-93, re: "EVOLUTION is wrong" > Evolution is observable? I thought it was supposed to be so > gradual and take so long that you could not observe it. Show me > an example. I do not deny certain changes within a species. I do > believe that humans and animals have been able to adapt to our > environment. Where I have a problem is evolutions theory that > there is a change from on species to another. Well, you may have a problem with it, but there is MASSIVE evidence indicating that new species do orginate from other species. Following this response I am going to enter (another) long multi-part message with the subject line "Speciation" which gives some examples and many references. I will offer some of my own first. > If evolution is supposed to be as gradual as they say, there > should be examples of animals that are in the state between in one > species and another. Actually there are numerous such examples. It must be understood that species actually tend to vary more in space than they do in time. What I mean by this is that the main, core, or central population(s) of a species tends to remain fairly stable in its form over extended periods of time; but a widespread species typically develops a number of geographical subspecies or races that show greater variety. (Keep this in mind when you read about "ring-species" below.) The fact is that equally well informed authorities will often disagree about when a certain group of organisms should be ranked as an independent species or as subspecies of an already existing species. Also, an individual scientists may recognize cases were such questions are not clearly resolvable and make what they fully realize are arbitrary decisions. This attests indirectly that there are indeed the "in between" states you deny. There is even a technical term -- semispecies -- for certain instances of an "in between" state. Below is a portion of the discussion of semispecies from Dobzhansky, Ayala, Stebbins & Valentine, 1977, _Evolution_, W. H. Freeman, p. 164. The term "sibling species" used here refers to species that are fully isolated in their reproduction (and are therefore good biological species), but in which the individuals are completely or virtually indistinguishable in terms of outward appearance or form: Mayr (1970) defines semispecies as "showing some of the characteristics of species and some of subspecies," and Grant (1971) as "populations [that] are neither good species but are connected by a reduced amount of interbreeding and gene flow." In other words, semispecies are borderline situations between races and species. Such borderline situations are bound to exist if the process of species formation is gradual rather than instantaneous. _Drosophila paulistorum_, one of the sibling species related to _D. willistoni_, is a complex of six semispecies. No outwardly visible characteristics by which one could distinguish the semispecies have been found. In laboratory experiments they manifest strong preferences for mating within their own semispecies. The ethological [behavioral, i.e., mating behavior] isolation, however, is less strong than between the sibling species. In crosses between these semispecies all hybrids are viable, but males are sterile. This incipient semispecies stage in the formation of species may be followed by a second stage where repoductive barriers are strengthened to the point where complete reproductive isolation is finally achieved. This is seen in process in this particular complex of semispecies. The behaviorally based isolating mechanisms are significantly stronger and more complex between those semispecies that inhabit the same geographical regions -- natural selection then actively favoring the development of such barriers due to the sterility of male hybrids -- and much weaker among those which inhabiting different regions. (Ayala and Valentine, 1979, _Evolving_, Benjamin/Cummings, p209.) This semispecies stage is, indeed, but one comprising a range of the genetic isolation which at one extreme defines fully distinct species. From Dobzhansky, et al, again, p192: The most detailed studies of allozyme variation between closely related species have been made in the _Drosophila willistoni_ group of sibling species. Five levels of evolutionary divergence are represented among these flies: A. Local populations of a species, which intercross easily and yeild fertile hybrids. B. Geograpically seperated subspecies, showing only a trace or no ethological isolation, but producing sterile male hybrids in at least one of the reciprocal crosses. C. Semispecies, geographically allopatric or sympatric (not inhabiting vs. inhabiting the same region), showing strong but not complete ethological isolation, and producing in laboratory experiments fertile female but completely sterile male hybrids. D. Sibling species, similar or identicle in external visible traits, yet giving rise to no viable hybrids in nature, and exhibiting strong ethological isolation. E. Reproductively fully isolated and morphologically distinguishable species. Dobzhansky et al give many other example of semispecies. The following page, for example, mentions two types of New Guinea birds of paradise which are so different in appearance that they had been classified in different genera, but which readily hybridize where their ranges overlap. The sources cited in the first quote -- Mayr, _Populations, Species and Evolution_, Harvard Univ. Press and Grant, _Plant Speciation_, Columbia Univ. Press -- also give examples. These are even more common among plants, where seperation between species generally tends to be more hazy than among animals. This is probably because plants cannot erect the kind of behavioural barriers to reproduction which animals can, and because polyploidy (changes in chromosome numbers associated with crosses) are much more common and viable. The later phenoma can even lead to nearly single step speciation events that can warrant new generic designations. But I will make it harder on myself and stick to animals. :-) I can't resist giving one more example of a somewhat different mode of speciation (in this case involving something called "the founder effect") with another example involving fruitflies. In this case a particular population of flies was literally caught in the act of evolving into a new species. Michael Ruse describes this in his book _Darwinism Defended: A Guide to the Evolution Controversies_ (Addison-Wesley, 1982) p108. Ruse has discussed a number of experiments in which reproductive isolation (the criteria of species seperation) had been produced in laboratory populations, and has turned to examples in nature: But, perhaps most exciting and pertinent of all to the whole question of the creation of new species is a series of observations and inferences about a certain population of fruitflies (_Drosophila pseudoobscura_) to be found in Bogota, Columbia. Through a combination of luck and informed intuition, Prakash (1972, "Origin of reproductive isolation in the absence of apparent genic differentialtion in a geographic isolate of _Drosophila pseudoobscura_," _Genetics_, 72:143-155) has been able to show that they are right in the middle of evolving into a new species, and that they exhibit just the characteristics one would expect were the principles of neo-Darwinism at work! In 1955 and 1956 extensive collection in Columbia yielded absolutely no members of _Drosophila pseudoobscura_, making it highly improbable that any existed. The nearest population was in Guatemala, 1500 miles away. However, _D. pseudoobscura_ started to appear in Columbian traps in 1960, suggesting that somehow it had been transported to Bogota, and now in some localities it is one of the most common of fruitflies. Moreover, tests show that already Columbian _D. pseudoobscura_ are starting to develope reproductive barriers with flies of the species collected from elsewhere. Although males from Bogota crossed with females from elsewhere produce normal offspring, females from Bogota produce totally sterile males when crossed with foreign _D. pseudoobscura_. New species are in the making! The Bogota flies show strong evidence of a species being produced as the population geneticist would expect. [...] Ruse proceeds to detail this last point, but since I am not going to take the time to explain neo-Darwinian theory and the models of speciation drawn from it I won't quote any further. Now, one more example of a type that I don't think is found in the text file which follows... This one has to do with what might be called "ring-species," of which there are a number of examples. In this phenomena a series of subspecies or geographical races of a particular species are arrayed ring-like in the suitable habitats around the periphery of some large ecological barrier like a mountain range or a dessert. I know of at least two such cases where two of the subspecies overlap in one place and are reproductively isolated with respect to one another, but where all the other subspecies readily hybridize with the adjacent subspecies. Normally such reproductive isolation would require that we classify the non-hybridizing subspecies as seperate species. But they are not separate species, being part of the same larger gene pool and reproductively connected indirectly the long way 'round the ring. In other words, you could start with one of the two overlapping but noninterbreeding subspecies and count two species if you go around the circle in one direction, but only one species if you go in the other! Here is the point of this... If the other subspecies in the ring should become extinct for some reason, those first two noninterbreeding subspecies are no longer connected and must thus be abruptly raised to the level of distinct species, even though they need not have undergone any genetic change themselves! This kind of example illustrates very nicely and simply a point which is also supported by detailed genetic analysis of closely related species and by the earlier examples involving fruitflies: The kinds of genetic change associated with the erection of reproductive isolation and the creation of new species are, in most cases, smoothly continuous with and not different in type from the kinds involved with variation that occurs within a species. Your position that you accept change and adaptation within a species, but not the origin of new species, is simply not tenable. Oh, yeah... Here are the two relevant cases of ring-species I know of: The warbler species _Phylloscopus trochiloides_, occupies a ring of habitats around Tibet, consisting, starting on the western side and going clockwise, of the following interbreeding subspecies... _viridianus_ --> _ludlowi_ --> _trochiloides_ --> _obscuratus_ --> _plumbeitarsus_ and back to _viridianus_. _plumbeitarsus_ and _viridianus_ do not interbreed. This is described in Cesare Emiliani, 1992, _Planet Earth_, Cambridge Univ. Press, p422. Emiliani cites Ernst Mayr's _Systematics and the Origin of Species_ (Columbia Univ. Press, 1942). The other example involves herring gulls which were actually classified as distinct species in Great Britian, _Larus argentatus_ and _Larus fuscus_. They are connected by a series of geographical subspecies that ring the north pole. I won't bother to give all the subspecies names in this case. My description of this case is from Colin Patterson, 1978, _Evolution_, British Museum (Natural History), pp6-9. He does not provide a primary reference, though I imagine I could find one elsewhere. I pause now to apologize to you and other echo readers for the bandwidth consumed by these messages. I will not be likely to repeat it to such degree in the future, but I am sometimes irritated slightly by the often fatuous and arm-waving manner in which creationists typically dismiss evolutionary theory as mere guesswork and rootless speculation. I wish to take this opportunity to give you some idea of the sheer mass of evidence tied to even one limited aspect of this supposed guesswork. A theory which has successfully brought coherence and integration to such a wealth of varied and detailed data may nevertheless be wrong, but it is not to written it off as easily as you would like to think is possible. --- FMail 0.92 * Origin: The OPEN FORUM S.D. CA (619)284-2924 v32bis (1:202/212)


E-Mail Fredric L. Rice / The Skeptic Tank