Yes, it's another damned evolution question...

[Elok]

But first, the disclaimer/notice(it worked last time, maybe it'll work again):
I AM NOT A FUNDAMENTALIST ATTACKING EVOLUTION. NOR AM I AN ATHEIST ATTACKING RELIGION. PERSONAL ATTACKS TREATING ME AS SUCH WILL GET NO RESPONSE FROM ME OTHER THAN A SPOT ON MY IGNORE LIST WITH YAVOON. THANK YOU.
AND PLEASE DON'T THREADJACK. PROSELYTIZE SOMEWHERE ELSE, I'M POSSESSIVE OF MY THREADS.

With that said, I seem to remember a response to a creationist in a previous thread that went along the lines of, "stop reading crap like Philip Johnson and look up 'transitional forms' from a reputable source."
As it so happens, I've since read Johnson's stuff(long story), and his argument seems aware of transitional forms but maintains that they do not exist, or at least haven't been found. Which is to say, no real, significant tfs that bridge the gaps between evolving types. There was a feathery dinosaur called archeopteryx and there is a primitive bird called the hoatzin, but he maintains to the effect that none of the freakish creatures that should have gone between have been found. I myself also wonder how such tfs could have reproduced unless by staggering coincidence similar aberrations appeared at the same time, seeing as cross-species breeding nowadays results in sterile offspring most of the time(tiglons, mules, etc.).
I ask mostly in the spirit of an inquiring mind here: do such forms exist, and if so, could somebody point me to a resource describing them? I've tried web searching but all I got was links to unfounded diatribes by either side of the issue. I'd like to reiterate that this is not an attack on the theory as such...

[Boris Godunov]

http://www.talkorigins.org/faqs/faq-transitional.html

Claims that there are no "transitional" fossils are bogus, because Creationists move the goal post whenever the evidence is presented to them. We have plenty of examples in the fossil record of marked "transition" in animals. Keep in mind that the further back you go, the more difficult it is to find intact fossils. Since speciesation occured such a long time ago in geologic history, the likelihood of finding fossils from that time is very remote.

[Dinner]

When I was still a university student I was lucky enough to take a class on evolution and the fossil record in which we got to see several claims made by creationists such as Johnson. Ussually, the creationist will stand around demanding a "missing link" or transitional form (which he claims is missing) then once a transitional form is found they go about trying to deny it is similiar species.

Personally, I think their sceptism improves the science by making scientists extra careful of what they publish. In the end these people won't except anything which doesn't confirm their religious beliefs so they cannot be concidered scientists.

[Japher]

I've seen a lot of stuff on discovery channel tracing, with fossils, the evolution of man...

[Dinner]

Lastly, you also have to remember that much of our understanding of the deep fossil record is based upon a handful of fossils from each species. That means scientists are never sure if they have a typical or atypical example of a given species. The scientific method just demands that people make up and test plausable theories based upon the evidience at hand so when new evidience surfaces (like when a new fossil is discovered) then you adjust your theory.

Many creationists seize upon this adjustmant as saying all of evolution is wrong because scientists move species A from being a sub-species of B into being it's own free standing species. The reality is the over all system is fine and the only thing people are arguing about is where individual fossils fit in.

[Boris Godunov]

Of course, since science is based on making predictions, just ask a Creationist what predictions he can make based on a Creation model, and an explanation for the transitional fossils we do have (like the walking whale found in 1993), and the varying levels of fossil strata that strongly support the evolutionary model.

[Az]

"They All go to heaven"?

[Urban Ranger]

Re: Yes, it's another damned evolution question...

Originally posted by Elok
With that said, I seem to remember a response to a creationist in a previous thread that went along the lines of, "stop reading crap like Philip Johnson and look up 'transitional forms' from a reputable source."

That's yours truly

Originally posted by Elok
As it so happens, I've since read Johnson's stuff(long story), and his argument seems aware of transitional forms but maintains that they do not exist, or at least haven't been found. Which is to say, no real, significant tfs that bridge the gaps between evolving types.

That's one of my biggest problems with Philip Johnson and his ilk. When overwhelming evidence presents itself, they just dismiss it with the wave of a hand.

Creationist, "I don't see how you can say birds evolved from dinosaurs. Where are the transitional forms?"

Evolutionist (goes around digging, eventually finds something that fits), "Hey, look at this marvellous fossil. It has both bird and dinosaur features. It is unmistakably a transitional form between birds and dinosaurs."

Creationist, "No it's not. It's just a freak accident."

Evolutionist, "What? WHAT??!"

Originally posted by Elok
I myself also wonder how such tfs could have reproduced unless by staggering coincidence similar aberrations appeared at the same time, seeing as cross-species breeding nowadays results in sterile offspring most of the time(tiglons, mules, etc.).

Why do you need these coincidences? These transitional forms could not be a result of corss-species breeding. For one thing, birds didn't exist. Anyway, As environmental conditions changed rapidly, individuals with certain mutations are favoured. As a result, they could survive and pass their genes to the next generation.

Originally posted by Elok
I ask mostly in the spirit of an inquiring mind here: do such forms exist, and if so, could somebody point me to a resource describing them?

Do they exist? No. Did they? Yes, of course. Otherwise, where did the fossils come from?

[Elok]

Well, UR, my point about the propagation was that the development of new species involves, naturally, a change in DNA. Different species tend to have different numbers of chromosomes(don't goldfish have 96 or something ridiculous like that?). Mutations resulting in different numbers of chromosomes in humans typically lead to things like Down's or Klinefelter's syndrome, which cause sterility, deformity, or both. Extra chromosomes have a hard time fusing with normal DNA into viable offspring. At least, that's the explanation I always heard. Now, different numbers of chromosomes aren't necessarily related to the development of difference between species, which is why this is only a minor, possible point of confusion w/me. I asked my dad this question once-he told me that chromosomal organization is an arbitrary biological filing system not related to viability. It still seems strange to me though...I'm not explaining myself very well, am I?
Boris: I think the word is speciation, BTW. Anyhow, isn't it a gradually ongoing process? The human race, as discerned from primitive pseudo-hominids, is only, what, two million? Pretty short time in the grand scheme of things. Not that far back. I thought it was pretty much dogma that evolution is ongoing. Actually, if it comes to that I guess there is a pretty smooth chain of developing hominids, just not for earlier species...so you have a solid point.

[Boris Godunov]

Elok:

On mutations:

http://www.talkorigins.org/faqs/mutations.html

talkorigins really is an incredible resource, I would advise giving it a very thorough reading when you have time.

And yeah, I was originally going to say something involving the word "species," but got short and time and lazy and added the -ization without deleting the rest. Oopsie.

Certainly, evolution is a gradually ongoing process [EDIT: not necessarily always, however, as Neutrino points out below, i.e. punctuated equilibrium]. We've even seen speciation occur, in a particular kind of dog that was transplanted away from its native habitat and, over 100 years, changed so it could no longer breed with the original species (I forget the instance, will have to look it up).

[Neutrino]

Hmm, I just took a final exam in my Evolution class last week

Speciation is the result of many possible factors, driven by both natural selection and neutral mutations.


To answer your question to the best of my knowledge, Gould came up with the idea of a 'punctuated equilibruim' model of evolution, where evolution basically occurs in spurts rather than at a constant rate (phyletic gradualism). Actual evidence from fossil records show evidence of both punctuated equilibria and phyletic gradualism. If a population of a species is undergoing rapid evolutionary change then the chance that fossils will be found for the 'transition' forms will be smaller than the forms that exist for a long time. This is just one of the possible explanations for holes in the fossil record. Note that similar traits can evolve indepently of each other -- i.e. convergent evolution and homologous traits.

As for hybrid inviability, it can result from difference in chromosome number. Humans have 46 c-somes - our diploid # (2n). Our haploid # is 23 (n). Gametes - sperm, eggs - are almost always haploid in the animal world. If the diploid # is odd, then the hybrid will most likely be sterile.

IMO the transitional forms were produced by a combination of hybridization and punctuated equilibrium evolution. Hybridization is hard to define concretely (hard to classify what exactly constitutes a species).

Hope this makes sense, groggy from lack of sleep.

[Ben Kenobi]

Actual evidence from fossil records show evidence of both punctuated equilibria and phyletic gradualism.

Do both models allow for the two to coexist? I would be interested to see how they workaround this problem.

Hybridization is hard to define concretely (hard to classify what exactly constitutes a species).

Nice to see this come from a non-Creationist. Clearly the non-Creationists are allowed to critique where the creationists are not.

[Neutrino]

Do both models allow for the two to coexist? I would be interested to see how they workaround this problem.

Most evolution is a mixture of the two. Punctuated equilibria and phyletic gradualism represent the 2 extremes. P.E. states that in between the rapid periods of change, the species remains stagnant. If we introduce phyletic gradualism into this scheme, the stagnant periods are replaced by a somewhat constant change. So we can have abrupt changes once in a while, and between those changes we can have a constant rate of change.

The whole concept of a species is rather hard to define - after all, how do we assign discrete groups to a continuous set (DNA/RNA). One of the topics that's being debated now in this field is how best to define a species. Personally, I prefer the Biological Species Concept (BSC) - species are groups of interbreeding natural populations that are reproductively isolated from other such groups [Mayr, and Dobzhansky and Huxley].

[Boris Godunov]

Originally posted by obiwan18
Nice to see this come from a non-Creationist. Clearly the non-Creationists are allowed to critique where the creationists are not.

When has an evolutionist ever asserted otherwise? And when have they criticized Creationists should they assert such a thing?

Actually, it is Creationists who tend to use this as a strawman. They assert that evolutionists believe in concrete hybridization, then argue against it and think they've scored some sort of tactical victory, when in fact they are arguing a position evolutionists tend not to hold, and one that is unneccessary for the mechanics of evolution.

[Urban Ranger]

Originally posted by Neutrino
Personally, I prefer the Biological Species Concept (BSC) - species are groups of interbreeding natural populations that are reproductively isolated from other such groups [Mayr, and Dobzhansky and Huxley].

That seems to be the most accepted definition.