Transitional Fossils

[Jose]

Creationists seem to claim that no transitional fossils have been found, thus disproving the theory of evolution. Evolutionists claim to have found very many of them. What's going on?

1. What is a transitional fossil?
2. What would one look like?
3. What are your criteria for coming to these conclusions?

I've put in the last question as an afterthought. It might help us resolve differences in our definitions.

[Jose]

On the other hand, converting one book into another is quite different. First, unlike actual evolution, it has a goal. That goal is: words, spelled correctly, in a specific sequence.

The mutating book example would not necessarily have a goal. The letters that would be changed would be purely random. The selection process would simply allow books that have meaning to continue to exist. Whereas books that have nonsensical words would be discarded. I think having a readable book would similar to a mutated organism that can survive.

But, to convert a book into a different book identifies that different book as the goal. Even to require that it is a book gives it a goal. But, this is less important than the next bit: selection would only enable books with meaning to exist.

If we have a reasonable book (ie, lots of pages), then viable mutations will change a sentence here, a sentence there, etc. As with biological evolution, the changes will be modifications to what already exists, and the modifications will be constrained by what is already there. This is why it isn't reasonable to expect mutations of one organism to be able to give rise to a rather different organism--because viable mutations are constrained by what is already present.

I'm not suggesting the the mutating book would have to go from a "Dick and Jane" to a "War and Peace" in one step. Rather, it would be many iterations of mutations/selections with many intermediate books in between.

But even choosing "War and Peace" gives us a goal. Certain words are required. Yet, "Dick and Jane" may not be able to give you those particular words and remain a viable book. You may be able to produce different books, but you can't predict beforehand what they will be. It may be that some of the mutations that would be necessary to produce "War and Peace" would make "Dick and Jane" unreadable, and you can't get there from here...which is why I suggested that viable intermediates might not be possible.

In both the book example and the human/oak example, there is no easy way to imagine how an intermediate, in between the starting point and the end goal, could be viable.

I would agree. But isn't this what common descent is asserting?

Yes and no. The book example and the human/oak example both envision conversion of one complex entity into a different complex entity. The details of the complexity are quite different in the beginning and end species. [eg: human cells without cell walls, oak cells with cell walls; the two books may use very different syntax and style.] If we try to mutate from one to the other, while retaining the complexity, almost everything we do is inviable. The only route I can think of right now is to delete the things that are specific to the starting species, then build up the things that are specific to the end species. That probably would be possible, but would have to go through a pretty basic intermediate (eg for the human/oak example, we'd probably have to go back to a single cell before we could add the cell wall without screwing things up.)

What common descent asserts is that there are intermediates, all right, but not intermediates in the conversion of one existing complex thing into a different existing complex thing. The intermediates are between existing things and ancestral things that no longer exist. In the case of the human/oak example, the ancestral thing is thought to be a single-celled organism that had mitochondria, but not chloroplasts, and was much less sophisticated than any extant unicellular organism. Once one individual organism of this species acquired a chloroplast, the plant and animal lineages diverged.

Similarly, we envision lobe-fins giving rise to amphibians, amphibians giving rise to reptiles, reptiles giving rise to birds--but certainly not by interconversion of the existing species of coelacanth to an existing species of frog, etc. The first amphibians were pretty crude models. The first amphibians had characteristics that could be modified to form crocodilians, turtles, lizards, dinosaurs, and pre-mammals--but they were constrained by what they had, and were not able to give rise to trout or dung beetles.

A better analogy for the book would be to start with one word, then create a bunch of mutations (by adding another word, to make two-word entities).

However, I would argue that the first organism's level of information would even exceed any book in existence. So, it should actually probably start off on the level of an encyclopedic set instead of a single word.

I think this may be a source of confusion. Sure, the common ancestor of humans and oaks had a lot of complexity--it was a living thing, after all. But to produce a human or a tree, it wasn't necessary to change all of this complexity--just modify bits of it. There is still a lot of genetic information that humans share with plants. Here, we need to consider a single-celled organism. Pop in a chloroplast, and you're on the route to oak trees. Allow cells to assemble into cell groups, and you're on the route to multicellularity. You've probably got something like algae and sponges. Give the multicellularity a bit more form, and a bit more cell specialization, and you've got simple animals and simple plants. Throw in cellulose walls for rigidity, and calcium-carbonate skeletal elements, and you've got something that can allow you to make bigger plants and bigger animals. etc etc etc

Throughout all of this, you still retain many of the features of the original species--the basic biochemistry and cellular physiology. You've just added some features and modified them bit by bit.

We can describe this progression because this is what both genetic data and the fossil record indicate. We'd never come to this progression if all we had was oak trees and humans, and we wondered how they came about. We'd be pretty skeptical of someone who claimed there might be an intermediate between the two...like an Ent, perhaps? Nope. In this case, the data indicate that the intermediate between these two was the last common ancestor, which was an extremely simple life form.

Similarly, with humans and chimps, there are no intermediates (in the sense of things that were conversions from one to the other). The last common ancestor was neither human nor chimp, but something else. There are intermediates between that something else and modern humans (even if we cannot say precisely whether a particular species was a direct, lineal ancestor of ours, or merely a cousin).

The intermediates are between ancestors and descendents, not between different families of descendents.

All of the information that is available to me has not provided a convincing argument for many points of evolution. And this information is not limited to creationist sources either, but many evolutionary sources. I would welcome exposure to the modern scientific findings on the evidence for evolution and be willing to explore them if brought up here.

We should explore some of these things. How about starting a thread on one or more of the issues you find uncertain? (We've had quite a bit of conversation on some things already; I'd be interested to learn whether the evolutionists here have said anything that helps with those topics. We may be saying things we think are clear and convincing, but in fact sound like gibberish.)

Maybe this is an important issue: the science is complex, while the common-sense arguments against it are not.

I would agree. In almost any professional field, it can get quite complex. The challenge is to make the information accessible and at least conceptually understandable to the layman. I believe that for most fields, it should at least be partially attainable.

I am reminded of Scientific American. When I read articles in my own field, I am astonished at how grossly over-simplified they are. When I read articles in other fields, I am equally astonished at how complicated they are--and realize that they must be as over-simplified as the articles I know something about. The same is certainly true of evolution--that the science is either simplified for clarity, at the expense of making the reader unable to verify whether it is true, or it is too complicated for most people to follow. Well, something must be attainable. Choose a topic (or wake up an existing thread), and let's see what we come up against. It should be fun, and will certainly be enlightening for me.

[rigadoon]

1. What is a transitional fossil?
2. What would one look like?
3. What are your criteria for coming to these conclusions?

I think the term "transitional fossil" is a way of saying that something should be there. In other words, for darwinism to be consistent with the fossil record, (1) it should show remains of organisms that are similar near each other; (2) it should not show remains of organisms that are dissimilar to each other and near each other; and (3) it should show remains of all types of organisms (the word type is ambiguous here). Since (2) would be a gap in the step-by-step sequence necessary for darwinism, the fossil record has been searched to find "transitional fossils" (or groups of similar fossils) so the fossil record could be assembled into a sequence of small differences from marine invertibrates to mammals.

[Jose]

Thanks, rigadoon.

I'll think about what you've said when I have more time. For now, I'll toss out a more specific question--an example of the issue I initially asked as a generality.

Suppose you have a species of lizard and, eventually, it evolves into a species of snake. What, according to your understanding of transitional forms, would the transtional forms be like? (If this were an ancient occurrence, we'd have transitional "fossils" instead of "forms," but I thought I'd use the generic term "form" here to make it easier to deal with). If you like, you can restrict the problem to "just the legs," and ignore the other anatomical differences. The legs will give us enough to work on.

I'll be back when I have time...

[rigadoon]

Thanks, rigadoon.

I'll think about what you've said when I have more time. For now, I'll toss out a more specific question--an example of the issue I initially asked as a generality.

Suppose you have a species of lizard and, eventually, it evolves into a species of snake. What, according to your understanding of transitional forms, would the transtional forms be like? (If this were an ancient occurrence, we'd have transitional "fossils" instead of "forms," but I thought I'd use the generic term "form" here to make it easier to deal with). If you like, you can restrict the problem to "just the legs," and ignore the other anatomical differences. The legs will give us enough to work on.

I'll be back when I have time...

I think this is backwards. We shouldn't go to the data with expectations. We should start from the data and work from there.

What should happen first is data collection: get observations of all the fossils. Of course there could always be more fossil finds and people are too anxious to wait anyway so in practice this means get a lot of fossils from all kinds of places all over the world.

Second, find patterns in this data. These are the "laws" of fossils -- not explanations, just descriptions of regularities. If you can put this into simple rules, so much the better.

Third, use these "laws" to "explain" that fossil x is in place y because of rule z etc. These are not metaphysical explanations, just working the rules in the inverse direction back to the data.

Fourth, take a break. There's more to life than studying fossils.

[Jose]

I think this is backwards. We shouldn't go to the data with expectations. We should start from the data and work from there.

Actually, it's not backwards. I accept your point, though--after all the noise I've made about developing inferences from the data, you'd think I'd want to start with the data. Actually, I do--additional data beyond the fossils themselves. I'll try to offer some reasoning:

It is essential to understand the constraints of biology before attempting to build models based on old rocks. When people argue that there are no transitional fossils, they reveal an incorrect assumption about their model of what evolution is "supposed to be."

Let's also think of it as going to the portion of the data that is composed of fossils, while also bearing in mind another portion of the data that is composed of genetics. Whatever model we come up with must be consistent with all portions of the data.

It is also relevant to ask: if we want to identify "transitional fossils," what criteria will we use? Here, we're defining the criteria--which is much easier to do in the context of an example than in a vacuum.

Have I persuaded you that this is a valid exercise?[/quote]

[rigadoon]

I think this is backwards. We shouldn't go to the data with expectations. We should start from the data and work from there.

Actually, it's not backwards. I accept your point, though--after all the noise I've made about developing inferences from the data, you'd think I'd want to start with the data. Actually, I do--additional data beyond the fossils themselves...

Let's also think of it as going to the portion of the data that is composed of fossils, while also bearing in mind another portion of the data that is composed of genetics. Whatever model we come up with must be consistent with all portions of the data.

It is also relevant to ask: if we want to identify "transitional fossils," what criteria will we use? Here, we're defining the criteria--which is much easier to do in the context of an example than in a vacuum.

Have I persuaded you that this is a valid exercise?

With data as vast as the fossil record there's a tendency to think of it as a complete record. If gaps are found, an argument from silence is legitimate, that the gaps mean something did not happen. If this undermines a particular model, then there may be an effort to find "transitional fossils" that fill the gaps.

So the question presupposes there's a gap. What are the criteria for a gap?

[Jose]

With data as vast as the fossil record there's a tendency to think of it as a complete record. If gaps are found, an argument from silence is legitimate, that the gaps mean something did not happen. If this undermines a particular model, then there may be an effort to find "transitional fossils" that fill the gaps.

So the question presupposes there's a gap. What are the criteria for a gap?

If there is a tendency to think of the fossil record as a complete record, it's misguided. The fossil record becomes more complete every day, as people find more fossils, but it is really no more than "those fossils that people have found." In the big game of connect-the-dots, it's just some of the dots--and "some" is pretty important. It's by no means all of the dots, or even most of them. So, by this logic, there are lots and lots of gaps.

Needless to say, people get interested in particular puzzles. If someone becomes fascinated by a particular evolutionary transition, then they will search for fossils that inform them of that transition. That is, they recognize a gap, and seek information that will help fill in the gap.

Here's an analogy, which happens to be used by creationists fairly often, but helps here:

I have fossils A (early) and Z (late). Are they related through common descent? Well, suppose we find fossil M. It's a "transitional fossil" perhaps. Aha! No it isn't. The true transitional fossils would be betweeen A and M, and between M and Z.

So, we find fossils H and Q. Well....the objection is that now the true transitional fossils are between A and H, between H and M, between M and Q, and between Q and Z.

By this logic, it seems that it should be possible (if evolution is true) to obtain all transitional forms and demonstrate the transition from A to Z. But, is it really? Creationists like to insist that the transitional forms between two other forms must be every step in a smooth morphing between the two forms. This makes sense conceptually, and is what Darwin envisioned, but it's not biologically accurate. It is necessary to understand the biology (specifically, genetics) in order to determine what a transitional form would be like.

I have left it vague like this, because I would still like to hear your current view as to what a "transitional fossil" would be like. Once we have this idea in mind, we can assess how it compares to genetic mechanisms. Maybe it will be the best description yet; maybe it won't. But we need to kick around the ideas before we can get much farther.

[micatala]

With data as vast as the fossil record there's a tendency to think of it as a complete record. If gaps are found, an argument from silence is legitimate, that the gaps mean something did not happen. If this undermines a particular model, then there may be an effort to find "transitional fossils" that fill the gaps.

I think most evolutionary biologists understand and accept that the fossil record is not complete. My understanding is we have found fossils representing some 250,000 species. Given that many millions exist today, it seems reasonable to say that many species that have existed in the past have not produced fossil specimens (or we just haven't found them yet).

With regards to a gap implying 'something did not happen' I am not exactly sure how to take this. A gap might mean that whatever did happen simply was not recorded in the fossil record. In such a case, the best we can do is provide an explanation for the data we do have. The fact that the explanation then implies that certain things happened 'in the gaps' for which we do not have evidence is not really evidence against the explanation at all. It simply means there are certain tests of the explanation that we cannot (yet) make due to lack of evidence. This does not invalidate all the tests that have been made (and passed) based on the evidence we do have.

[Jose]

rigadoon--I'll refer back to an older post:

1. What is a transitional fossil?
2. What would one look like?
3. What are your criteria for coming to these conclusions?

I think the term "transitional fossil" is a way of saying that something should be there. In other words, for darwinism to be consistent with the fossil record, (1) it should show remains of organisms that are similar near each other; (2) it should not show remains of organisms that are dissimilar to each other and near each other; and (3) it should show remains of all types of organisms (the word type is ambiguous here). Since (2) would be a gap in the step-by-step sequence necessary for darwinism, the fossil record has been searched to find "transitional fossils" (or groups of similar fossils) so the fossil record could be assembled into a sequence of small differences from marine invertibrates to mammals.

Aha! Let me rephrase it: Evolutionary theory proposes that current species evolved from earlier species, which evolved from even earlier species. According to this theory, there should be a continuous lineage from one species to the next--i.e. there must be transitional individuals along the way. How would these transitional forms be recognized? What would they look like?

That is, we are asking what should exist if the theory is correct. This is, in a sense, a way of testing the theory. If transitional forms must look like XXXXX, but XXXXX is never, ever found, then it would seem that the theory cannot be correct. Needless to say, this test of the theory depends on the predictions of what the transitional forms should look like.

If we think of it this way, then we are asking about a theoretical consideration, in the theoretical event that the theoretical model might, theoretically, be correct. Theoretically, that is.

Now, let's see...

(1) similar organisms should be near each other. I infer that you mean "near" in terms of geological age, rather than locale. In the same locale--western Kansas, for example--we can find fossils of mosasaurs, giant clams, and ammonites. The nearness of these indicates that they lived in the same shallow sea at the same time. Needless to say, things that live at the same time cannot be each other's ancestors. The trouble with "near" in terms of time is that there may well be migration from place to place. To conjure up an image, we might find the ancestors--and therefore "transitional fossils" of the (Cretaceous) Kansas ammonites in (Jurassic) Colorado, and we might find their ancestors in (Triassic) New Jersey, and their ancestors in (Permian) Texas, etc. [I chose these locations simply because I know of fossiliferous ocean sediments in each of them.] So, "nearness" is a bit tricky.

(2) there should not be dissimilar organisms near each other. I've mentioned this already, but I'll do so explicitly here. If an ecosystem is buried, and thus capable of fossilization, we expect to get fossils of a representative sample of the species that lived there. To some extent, this is what we find--although people tend to focus on their favorite species. The Petrified Forest is thought of as "trees." It's actually an entire swamp ecosystem, with other plants, and with lots of different animals. So, we actually do expect to find lots of dissimilar organisms near each other--the ones that lived in the same ecosystem.

(3) the fossil record should show remains of all types of organisms. Yes, it should...filtered through the "lens" of "how fossils work." Aquatic species with hard parts are more likely to be fossilized than terrestrial species because they are more likely to be covered in sediment. Anything without hard parts is likely to be mooshed before it gets buried, and not so likely to be buried by really fine sediment that could preserve it. The probability of fossilization is low, and also non-random because some things are in places that are more likely to be buried before they decompose. Then, when fossils are exposed on the surface, they have a limited lifetime before they erode away. So, the majority of fossils are lost to erosion, rather than found and collected. All we can actually say, ever, is that the fossil record is "currently known" to contain "the fossils we know about."

I think your 3 criteria here are good, and make sense. But, I imagine that they will not be particularly practical for distinguishing "who's who" among fossils. So, I'll go back to my prior suggestion, that we think about a particular evolutionary transition, and describe what the intermediates in that transition should be like. I suggest the "ancestral lizard-like" animal and its eventual descendent, the snake. What should some of the transitional forms look like? With a specific example, I think we can discuss the issues more clearly.

[plunge23]

It's worth noting that animals that lived and died in acidic forests or wide open plains are almost never going to show up as fossils, because in both cases there is no buildup of hard sediment over time, and tons of decaying forces to destroy the corpse long before it can become imprinted on anything.