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Evidence for the Theory of Evolution?

     Posted by Mockingbird1 on September 08, 1998 at 00:41:35:

     PK: I've argued the thing about nature selecting those attributes which promote survival and reproduction. The theory of evolution suggests that species originate from other species. Since post-zygotic (post-mating) isolation is observed between some species, I see an inconsistency in the theory of evolution, since selection of post-zygotic incompatibility would inhibit reproduction w/in a population. (self pity on)I have been mocked and belittled for suggesting I see something wrong with a theory which is enjoyed by smarter and more learned minds than my own. (self pity off) I've been told that the evidence supports the theory and illustrates my concerns are not expressed in nature. I'd suggested a review of a set of observed speciation incidents from TO.

     PK: Joe M., major geologic asset that he is, pointed out empirical evidence for the theory of evolution, and I asked him about it below. Joe appears to be busy elsewhere. So, anybody want to look over the quick recap and maybe find something on instant replay, that I missed?

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     PK: A quick recap:

     PK: Paragraph 5.1, about 9 instances of observed speciation, all events, distinct from evolution.

     PK: Paragraph 5.2.1, two similar species living in the same region with diminished fertility in hybrids - not an observation of speciation, much less evolution. 5.2.2, similar to 5.2.1 - different plants. 5.2.3, drum roll please - speciation via evolution, specifically adaptation to a toxin.

     PK: Running talley - non-evolution - about 9, evolution - 1.

     PK: Paragraph 5.3. One for speciation via parasitic infection, eight or nine developing assortative mating, one to the extent of speciation. Ding, ding, that is two, count 'em 2, for evolution!

     PK: Running talley - non-evolution - about 10, evolution - 2.

     PK: Paragraph 5.4. - three experiments with assortative mating.

     PK: Running talley - non-evolution - about 10, evolution - 2.

     PK: Paragraph 5.5. - Two more cases of assortative mating

     PK: Running talley - non-evolution - about 10, evolution - 2.

     PK: Paragraph 5.6 - one more asortative mating, next!

     PK: Running talley - non-evolution - about 10, evolution - 2.

     PK: Paragraph 5.7 - Ding! ding! Another score for evolution! Adaptation to unspecified toxins causes reproductive isolation. Darwin was right, just like my broken watch!!!! The tying run is on base (after the team bats through the line-up)

     PK: Running talley - non-evolution - about 10, evolution - 3.

     PK: Paragraph 5.8 - Two more speciations via bacterial infestation

     PK: Paragraph 5.9 addresses ambiguous cases. The total count of observed instances of speciation, where speciation occurred, was 15. Of these, three were due to evolution.

     PK: So, just what empirical evidence does favor the theory of evolution?

     PK: To answer the interesting question, I'd say it looks like a gee string since evolution might actually cause some speciation, in unusual cases.

     v/r

     Pat

     TO link (http://www.talkorigins.org/faqs/faq-speciation.html)

First Response

     Posted by Adam on September 09, 1998 at 07:37:43:

     Mockinbird1: Since post-zygotic (post-mating) isolation is observed between some species, I see an inconsistency in the theory of evolution, since selection of post-zygotic incompatibility would inhibit reproduction w/in a population.

     Adam: Post-zygotic barriers

     1. Hybrid inviability- zygote is aborted
     2. hybrid sterility- offspring cannot produce gametes example is the mule which is the product of a horse by donkey cross.
     3. hybrid breakdown

     First F1 may be fertile, but by the F2 these are usually feeble and sterile.
     Yet with these barriers, introgression may still occur. Hybrid between two species may breed with one of the two parent species introducing alleles from the other species into the other species. Plant breeders have used this to introduce new traits into domesticated lines of plants from wild species of the same genus.
     The evolution of these genetic barriers to gene flow is the key to speciation - the elevation or evolution of new species. Remember the effect of gene flow is to homogenize populations- make them more alike while natural selection tends to accentuate differences but not always- remember stabilizing selection mode. -speciation website (URL unavailable).
     I still don't see what the problem is.

     Posted by Mockingbird1 on September 09, 1998 at 22:43:18:

     PK: Thanks for sharing the potential to exploit partial incompatibility.

     PK: The problem that I see is that those elements of a population which experienced post-zygotic isolation from their population would be less successful reproducers (due to the isolating factor). Though they may be artifically selected for (through numbers of crosses or whatever) they would be naturally selected against. With the deselection, the strain extinguishes rather than becomes a new species.

Second Response

     Posted by MEYER on September 09, 1998 at 22:50:37:

     You say speciation via-evolution. Then you say "One for speciation via parasitic infection, eight or nine developing assortative mating, one to the extent of speciation."

     I can't understand how evolution causes speciation. Evolution is the term used for the result of speciation isn't it?
     No matter what the cause, once speciation is observed, evolution has been observed, has it not? I do not believe speciation over time causes common descent, but I do agree speciation is evolution.

     Posted by Mockingbird1 on September 09, 1998 at 23:05:40:

     :MEYER: I can't understand how evolution causes speciation. Evolution is the term used for the result of speciation isn't it?

     PK: Mating preferences may change as environments change. When two groups can't interbreed (sometimes becuase they refuse to interbreed) they are two species. It may be temporary as the environment changes over thousands of years, but to the extent that the term species is understood, what was one is now two, when they split of their own chosing or due to post-mating isolation (sterile, or no offspring).

     :MEYER: No matter what the cause, once speciation is observed, evolution has been observed, has it not? I do not believe speciation over time causes common descent, but I do agree speciation is evolution.

     PK: Different terms are used because different meanings are implied. Evolution is process of gradual change; your dog giving birth to a cat would not be evolution - the change of species was not gradual. Change of frequency of alleles in a population will occur as the population adapts to its environment - evolution without speciation.

     PK: Speciation is simply the origination of a new species, typically with observation of reproductive incompatibility with the ancestor population. Either they won't get together, or when they do, the baking doesn't bring the buns out of the oven (using highly technical jargon).

     PK: Theoretically, it should be possible that speciation may occur by means other than evolution. That most speciation is by other means suggests a falsification of the theory. (homor on) Please don't tell the evolutionists that their theory might be falsified. I would never want to provoke a discussion of the theory on its own merits. (humor off)

     Posted by MEYER on September 09, 1998 at 23:36:40:

     Change of frequency of alleles in a population will occur as the population adapts to its environment - evolution without speciation.

     Agreed. However, whatever caused the change in allele frequency, it's still evolution-or change in allele frequency.

     PK: Theoretically, it should be possible that speciation may occur by means other than evolution.

     But, it would still result in a change in allele frequency, hence it is still evolution, right?

     Posted by Sumac on September 10, 1998 at 00:01:42:

     PK, you have it backwards. It is not speciation by evolution but evolution by speciation. There are many mechanisms of speciation. Long-term divergence by genetic drift of isolated populations would be just one of those mechanisms. In each of the examples you cite, there has been some event that has caused reproductive isolation. In some cases it is geographical isolation, in other cases it is infection, in yet other cases it changes in ploidy, and in some other cases it is chromosomal translocation. In all cases, however, it is evolution.

     Posted by Mockingbird1 on September 10, 1998 at 08:45:12:

     PK: Is or isn't evolution a gradual process?

     PK: When one generation of a population yields a different species, we are looking at two populations. It becomes difficult to talk of changes in allelic frequencies in a population when you are talking about two different populations.

     PK: I don't think I am confused, critical, yes!

     Posted by Helen on September 10, 1998 at 10:53:02:

     At the very least it would sure be a money-maker!

     Posted by Mockingbird1 on September 10, 1998 at 11:16:13:

     PK: When MEYER observed that dogs don't give birth to cats and that that suggested problems with the theory of evolution, Pat corrected him.

     PK: Subsequently, when evolutionists assert that species 'A' producing species 'B' in one generation or less, is in fact evolution.

     PK: Seems the goalposts move predictably. When a creationist says something wrong, the evolutionists say it is wrong; when the evolutionists say the same thing and they are corrected, the creationist is 'confused'. I am not confused! I don't like to see creationists play switch with the argument, as Greg did months ago. I don't find the practice particulary more tolerable when done by evolutionists.

     Posted by Sumac on September 10, 1998 at 19:35:02:

     We can disagree on the details yet still agree on the general concepts. Evolution, in my mind, is simply a change in life over time. There are multiple mechanisms and types of change. If you have a problem with that definition, I'm sorry.
     Speciation is a mechanism of change. It causes one population to become two. Now each population is free to change independently of one another. How the speciation has occurred is irrelevant. The point is that what was one is now two. Again, evolution is not a mechanism of speciation, speciation is a mechanism of evolution (i.e change).
     You've probably already read Deb's post. I mostly agree with what she said. I just wouldn't use the definition of "a change in allele frequency over time".

     [Deb's Post was linked in the original. Here is the content:

     (I shouldn't be doing this, because I swore I would not get involved in another of Mockingbird's endless 'is not is too' debates, but since it's you that asks...(-:)
     "Change in allele frequency" is supposed to cover it, but unfortunately while it does broadly define evolution, it does not do a very good job of conveying the complexities of evolutionary theory. The fact of evolution is change of allele frequency, and common descent (hold the froth til later--I'm just stating current evolutionary facts). The theory of evolution is HOW the "facts" came about. For example: just what is the importance of natural selection versus genetic drift? Are there varying rates of change? How important is contingency? How important is adaptation? Is allelic change all that is needed for macroevolution, or is "species selection" important as well?
     These are just some of the ideas that get kicked around with various degrees of vigour. Speciation, whatever the cause, is evolution--macroevolution. Trying to distinguish between a "process' and an "event" is specious, at best. "Events" are probably the cause of most speciation, whether they be "slow" events such as geographical separation of populations, which cuts off gene flow between them to some degree (or entirely), or a "fast" (i.e. observable in our lifetimes) event such as infestation. The end result is that a population no longer changes the same alleles as the rest of the population.
     As far as behaviour--strictly speaking, I would think it results from the evolutionary history of the organism. Birds dance and display their feathers because those that did it best left more of their genes behind relative to those who weren't so good at it. Human behaviour, of course, is far more complex--while there is certainly an evolutionary legacy to it--we still eat, reproduce, defend our young/territories, form social groups and all that--we also have evolved the ability to consider what we do in something other than purely naturalistic terms (there is a debate on how this ability came about--is it an epiphenomenon of having lots of neural connections and a highly convoluted cortex, or not?). So there is some feedback on the evolutionary consequences of human behaviour, because we can choose to modify our behaviour based on criteria that have nothing to do with adaptation.
     Hope this helps (and I hope you can infer the IMHO).

     Deb]

     Posted by MEYER on September 10, 1998 at 20:03:53

     After a long period you all had finally convinced me that evolution was indeed a fact. Not common descent, but speciation and change in allele frequency. Now it turns out the definition I have been given "change in allele frequency over time" may be wrong. It goes back to what I defined it over a year ago, change over time.
     You guys tell everyone, "learn what it says". But you all don't even know. How can you expect anyone to believe in the theory as a fact, if you don't even have a clear definition? Pat even told me once evolution is a very precise theory. Wrong! It doesn't have a precise definition, so what could be precise about common descent? Inference is your fact, and jargon is your definition.

     Posted by Deb on September 10, 1998 at 20:53:54:

     --you really do not read very well sometimes. Sumac and I in no way implied that "change in allele frequency" is wrong, but possibly incomplete. It tends to be used most often simply because it conveys the idea of both change over time and a very common mechanism for that change. But not every mechanism in every circumstance, and there really is no definition that catches all the complexity and nuance that is involved.

     Posted by Mockingbird1 on September 10, 1998 at 23:46:31:

     PK: I know how tempting it can be to tell Deb they got a worse case of the religious mumbo-jumbos then a bunch of seminary students, but, Deb did not say it is a Mystery. She says it is undefined. It is not the same, just tempting. I thank Deb for trying to help out against her better judgement. If they could explain the theory of evolution, they could teach it successfully in high school. So don't sweat it; I don't get it either.

     PK: Maybe we are different because we won't pretend we understand it until we do. Or maybe we really are disabled.

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