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.

[rigadoon]

Jose,

Let's start at the beginning with a hypothesis that looks for evidence in the fossil record. What is the hypothesis? You tell me -- and express it in terms of fossils. I presumed the hypothesis had to do with the possibility of assembling fossils in a series in which the difference between any two adjacent fossils is small. Of course this series shouldn't be arbitrary but should somehow reflect the locations of fossils (or some metric).

But what you've been saying is that the fossil record has characteristics that interfere with the construction of such a series -- but the hypothesis is sophisticated enough to handle these. So what a priori hypothesis about the fossil record do you have? If this involves a series, then the the fossil record should show a series.

[Grumpy]

rigadoon

You seem to be demanding a movie or claymation cartoon as the only acceptable fossil evidence of transition. I'm sorry, all we have is hundreds of thousands of snapshots capturing moments in time, some of which are of poor quality or have only partial info.

Does that mean we must reject them as conveying no information??? NO!!! Like a gigantic mosaic jigsaw puzzle(where each piece is a picture on it's own) with some missing pieces, the more we can assemble, the clearer the big picture becomes. And we are continually finding more of those missing pieces! We will probably never find evidence for every creature depicting every little change(though for some creatures we have) but that does not mean that the modifications did not occur in the periods we have no fossil for or that we cannot trace the lineages of those creatures with a good level of confidence.

And then we have the fossils of creatures like Archeopteryx where the transition between two types of creature is evident for all to see. These are the fossils which are called transitional, but in reality they all are creatures in transition from what their predessesers were to what their descendents will become, it's called evolution and it is in fact supported by huge amounts of fossil evidence.

Grumpy 8)

[QED]

Of the 300 million or so people living in the US right now, how many do we think would make it into the fossil record (assuming that everyone was left where they fell ). That would be the number who fell and were quickly covered by sediment or mudslide. And that's the number that would enter the Geological column. How many individuals would ever exit the Geological column in some future excavation?

Gould estimates that 99% of all plant and animal species that have ever lived are now extinct and that most of these have left no fossil evidence of their existence. Some e.g. Raup (1991) put the figure at 99.9% But within an order of magnitude or so this would mean that several billion different species would have inhabited this planet during it's history. The number of fossil specimens that have actually been collected and studied is vanishingly small by comparison.

[Jose]

Let's start at the beginning with a hypothesis that looks for evidence in the fossil record. What is the hypothesis? You tell me -- and express it in terms of fossils. I presumed the hypothesis had to do with the possibility of assembling fossils in a series in which the difference between any two adjacent fossils is small. Of course this series shouldn't be arbitrary but should somehow reflect the locations of fossils (or some metric).

But what you've been saying is that the fossil record has characteristics that interfere with the construction of such a series -- but the hypothesis is sophisticated enough to handle these. So what a priori hypothesis about the fossil record do you have? If this involves a series, then the the fossil record should show a series.

So you don't want to do it the correct (ie my ) way? We'll have to get there anyway, because it's an essential step. Well, OK...here's one. It's been published, so it's been vetted by the competitors.

What was the rate of demise of dinosaurs at the end of the Cretaceous? There are (were) two contending hypotheses: slow decline, perhaps as a result of global climate change, or rapid decline, perhaps as a result of a catastrophe of some kind. The first hypothesis makes the prediction that, as we get closer and closer to the K/T boundary (Cretaceous/Tertiary), the abundance of dino fossils should decrease, until they kinda peter out altogether. The second hypothesis makes the prediction that the abundance should be fairly stable, only to change abruptly at the iridium band.

OK...to test the hypothesis, the researchers engaged a very large number of people to scour the Hell Creek Formation at Hell Creek, Montana. This is several hundred vertical feet of exposure, from somwhat above the nominal water level of Ft. Peck reservoir to the tops of the Missouri River bluffs. The Hell Creek overlies the Fox Hills Shale, which is from an aquatic environment (ammonites, not dinosaurs), and conveniently defines the bottom of the series.

So, they did this. With a huge sample size, carefully identified as to site of origin, they concluded that the abundance of dino fossils was pretty constant up until the K/T boundary.

So there you are.

I note that you've made an assumption...it seems to be that palenotologists define "an evolutionary series" on the basis of "what looks good"--you know, get the fossils, then line 'em up however you like. It doesn't work that way. The order is determined by the geological strata in which the fossils were found. Oldest first, youngest last.

Another assumption is that one starts with an hypothesis. I know, the textbooks say there is such a thing as "The Scientific Method," but they're wrong. Each field uses its own logical methodology. Each researcher, and each project bump around among the various thought processes that make up "figuring things out." With the fossils, what you find determines the hypotheses that you can propose to explain the data. So, for example, in the early Devonian, you find fish. You find no land animals. By the Pennsylvanian, you find amphibians on land. In the late Devonian, you find some fish in which the proximal fin bones are larger than in other fish; and you find other species of fish in which the proximal fin bones are much smaller, and the distal "ray" bones are longer. In the Silurian, you find ocean fish that are like the latter--rays in the fins. You find other fish that are in coastal swamps, which are more like the other type of fish--the "lobe-finned" ones. But, these guys have somewhat larger proximal fin bones. By the end of the Silurian, the ocean fish are pretty much like normal fish, but the ones in the swamps (at least, in swamps that eventually became Greenland) have fins that are even more robust, and kinda look like legs, albeit with the feet sideways to act like paddles. In the early Mississippian, you find critters whose fins have the feet beneath them, like feet, rather than sideways, like fins. And some of these are associated with fern fossils, not underwater swampy stuff.

So, there's the data. What do we make of it? The hypothesis is drawn from the data; it's the explanation of the data. It may, if we use The Scientific Method, become the hypothesis that we can test in another investigation, but for now, it's the inference drawn from the data.

What inferences make sense? Well...there's

• the designer kept changing her mind about what she wanted on the earth
• life disappeared periodically, and then reappeared in somewhat different forms
• genetic continuity being what it is, the earliest animals were the ancestors of the later animals, which were the ancestors of the youngest animals in this series
• of course, the ocean fish and the swamp fish are quite different from each other, even though the ancestors suggested by the data were the same
• so, maybe, the ancestral fish, with both proximal limb bones and distal rays, gave rise to two different lineages, in one of which the rays developed, while the proximal bones were lost, and in the other of which the proximal bones developed and the rays were lost.

OK...here are three hypotheses that explain the data. One is natural, one is supernatural, and the third is just weird because we have no clue how it would work. Now we can make predictions based on these hypotheses, in order to try to distinguish them. The third model predicts that, as we get more and more fossils across this time interval, we'll be able to fill in the gaps (ie, find fossils from times that we currently don't have fossils from). The second model predicts that there might be gaps in which there are no fossils at all--the times between the disappearance of life and the reappearance of life in a different form. The first model predicts...why, nothing at all. The designer could do anything she wants.

OK...for the fossils that we expect to find throughout this time interval, and that should be the continuous extended family of these critters, what might we predict for the appearance of the fossils, if they are really, truly, intermediates between fish and amphibians?

[micatala]

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.

I am going to pick a little nit here, even though I am far from the expert that Jose is on all of this.

Yes, i agree we could say that 'if the theory is correct, then XXXXX should exist'. However, the fact that XXXXX is never found does not necessarily mean the theory cannot be correct; it merely means that a piece of evidence that we would like to have has not (yet?!) been found.

Sort of like a prosecutor who would of course always like to find the murder weapon, but even if the weapon existed, might never be able to produce it for the trial. He or she still might be able to obtain a conviction, even without this valuable piece of evidence.

As you have noted, fossilization is an uncommon and not completely random occurrence. Even for species that have a higher probability of fossilizing, it seems to me that it is still possible that we might never find specimens of the species. I am curious: has anyone ever done an analysis of 'given conditions A, B, C, etc. on a species and its environment, there is a p% chance we will find a fossil specimen within N years' or something like that?

[Jose]

If transitional forms must look like XXXXX, but XXXXX is never, ever found, then it would seem that the theory cannot be correct.

Yes, i agree we could say that 'if the theory is correct, then XXXXX should exist'. However, the fact that XXXXX is never found does not necessarily mean the theory cannot be correct; it merely means that a piece of evidence that we would like to have has not (yet?!) been found.

Well said! If I lose my marbles, and no one finds them, does this prove I never had any? It proves only that no one has found them. I could quibble with semantics, and hide behind "never, ever." "Never, ever" implies a very long time...

You're right. Failure to find something is simply failure to find it. It is not proof that it never existed. Maybe we could imagine that I simplified the argument to make it more digestible?

[rigadoon]

What was the rate of demise of dinosaurs at the end of the Cretaceous? There are (were) two contending hypotheses: slow decline, perhaps as a result of global climate change, or rapid decline, perhaps as a result of a catastrophe of some kind. The first hypothesis makes the prediction that, as we get closer and closer to the K/T boundary (Cretaceous/Tertiary), the abundance of dino fossils should decrease, until they kinda peter out altogether. The second hypothesis makes the prediction that the abundance should be fairly stable, only to change abruptly at the iridium band.

"Slow decline" vs. "rapid decline" indicates what -- the number of fossils expected (large vs. small) or how close the fossils are to one another (near vs far)? Some method of determing closeness would be needed for the latter.

OK...to test the hypothesis, the researchers engaged a very large number of people to scour the Hell Creek Formation at Hell Creek, Montana. This is several hundred vertical feet of exposure, from somwhat above the nominal water level of Ft. Peck reservoir to the tops of the Missouri River bluffs. The Hell Creek overlies the Fox Hills Shale, which is from an aquatic environment (ammonites, not dinosaurs), and conveniently defines the bottom of the series.

So, they did this. With a huge sample size, carefully identified as to site of origin, they concluded that the abundance of dino fossils was pretty constant up until the K/T boundary.

Abundance, as in large number, not closeness?

I note that you've made an assumption...it seems to be that palenotologists define "an evolutionary series" on the basis of "what looks good"--you know, get the fossils, then line 'em up however you like. It doesn't work that way. The order is determined by the geological strata in which the fossils were found. Oldest first, youngest last.

OK, the metric is strata. Within strata there is no order?

Another assumption is that one starts with an hypothesis. I know, the textbooks say there is such a thing as "The Scientific Method," but they're wrong. Each field uses its own logical methodology. Each researcher, and each project bump around among the various thought processes that make up "figuring things out." With the fossils, what you find determines the hypotheses that you can propose to explain the data.

Wait a minute. Certainly you should start out just observing, not hypothesizing. But at some point hypotheses need to be made before looking at new data. That's the only way to test a hypothesis. Anyone can make up a post facto explanation.

So, there's the data. What do we make of it? The hypothesis is drawn from the data; it's the explanation of the data. It may, if we use The Scientific Method, become the hypothesis that we can test in another investigation, but for now, it's the inference drawn from the data.

A statistical data analysis will lead to a summary of the data, which may inspire a hypothesis. For example, a regression line may be y=2.01x. A scientist may look at that and think, "That's close to 2" -- and think of a reason why 2 would make sense and so hypothesize a functional relationship y=2x.

OK...for the fossils that we expect to find throughout this time interval, and that should be the continuous extended family of these critters, what might we predict for the appearance of the fossils, if they are really, truly, intermediates between fish and amphibians?

Intermediates? That supposes a series. You say nothing about a series. So the fossils show no spatial series that can be interpreted temporally (other than strata)?

[Jose]

"Slow decline" vs. "rapid decline" indicates what -- the number of fossils expected (large vs. small) or how close the fossils are to one another (near vs far)? Some method of determing closeness would be needed for the latter. ... Abundance, as in large number, not closeness?

The "decline" indicates the change in abundance; "abundance" is number per unit area. So, it's both large number vs small number and closeness (because lots of fossils in a square mile = fossils close together; few fossils per square mile = fossils far apart).

OK, the metric is strata. Within strata there is no order?

There is order, with every named Formation or Member subdivided into the layers of specific rock types, and sometimes layers within those layers. And, of course, a thickish layer has a bottom, middle, and top. So, there's lots of order.

Another assumption is that one starts with an hypothesis. I know, the textbooks say there is such a thing as "The Scientific Method," but they're wrong. Each field uses its own logical methodology. Each researcher, and each project bump around among the various thought processes that make up "figuring things out." With the fossils, what you find determines the hypotheses that you can propose to explain the data.

Wait a minute. Certainly you should start out just observing, not hypothesizing. But at some point hypotheses need to be made before looking at new data. That's the only way to test a hypothesis. Anyone can make up a post facto explanation.

Exactly right. I think we're saying the same thing. When I say "what you find determines the hypotheses," I'm using alternate phrasing for "the initial observations invite hypotheses to explain them." Then, as you say, the next step is to test the hypothesis (if your branch of science works that way).

I keep waffling here because my field doesn't use The Scientific Method as it is traditionally defined. Very few fields do. What we do is "ask questions" and use the experimental data to help us answer those questions. In our research papers, we identify the questions, describe the methods and the results, and then develop our models. The models/explanations/hypotheses are the inferences from the data, and constitute the Finale of the research paper.

A "Scientific Method" paper, on the other hand, presents the hypothesis to be tested at the beginning, then describes the methods of the test, and the results of the test. The Finale is either "thus the hypothesis is ruled out," or "the hypothesis is not ruled out."

Although the logic and thinking seem so different, once you get going (after the initial observations that got you started), it's a continuous sequence of experiment --> data --> hypothesis/model --> experiment --> data --> hypothesis/model etc. The Scientific Method requires that you put the hypothesis at the beginning of the paper; other fields put the hypothesis at the end of the paper. Fields that do it one way typically make fun of fields that do it the other way. But, either way, the data/observations are what hypotheses are based on; more data/observations are what test hypotheses that have previously been formed.

A statistical data analysis will lead to a summary of the data, which may inspire a hypothesis. For example, a regression line may be y=2.01x. A scientist may look at that and think, "That's close to 2" -- and think of a reason why 2 would make sense and so hypothesize a functional relationship y=2x.

Whether the scientist simplifies 2.01 to 2.00 depends on whether the simplification is justified. It may not be. If someone makes up a rationalization for rounding to 2.0 when such rounding is not justified from the data, they will eventually be proved wrong.

In any event, statistical analyses are not always possible. Indeed, in my field, it is often said "if you need to use statistics, you didn't design a clean experiment." In other types of analysis, statistical analysis is essential. As with much of what we've talked about, it isn't always appropriate to make broad generalizations.

OK...for the fossils that we expect to find throughout this time interval, and that should be the continuous extended family of these critters, what might we predict for the appearance of the fossils, if they are really, truly, intermediates between fish and amphibians?

Intermediates? That supposes a series. You say nothing about a series. So the fossils show no spatial series that can be interpreted temporally (other than strata)?

I highlighted in blue the "supposed series." The evolutionary model, derived from the data, is that we have a continuous family lineage. By definition, this is a series. Like any family, grandparents give rise to parents, which give rise to children, which give rise to grandchildren, which give rise to great-grandchildren, etc. Here, the model is that this family went on for a very long time, and that the great-great-great...great-grandparents were fish; the great-great-great...great-grandchildren were amphibians. The changes in limb structure along this continuous lineage, according to the model, result from mutations in genes like Hox, shh, fgf, etc.

So, yes: this supposes a series. There should be intermediates. That is the hypothesis we'd like to test. To test an hypothesis, it is necessary to articulate what that hypothesis is (I did that above), and articulate the predictions the hypothesis makes. Then, one asks if those predictions are met. The general appearance of the intermediate fossils is one of those predictions.

Hmmm...spatial series? There's the vertical aspect of spatial (strata) as you say. The horizontal aspect may, or may not make sense...we may have to collect the data before we can propose explanations for it. We know that some of the later fossils in this series ("series" being loosely interpreted here to mean "any of the critters that look like something between 'fish' and 'amphibian'") were found in New Jersey (or was it Pennsylvania?), while the earlier ones have been found mostly in Greenland. I'm not sure yet what this tells us, if anything.

By contrast, the analogous fossil series for whales has the oldest ones--4-legged land animals--only in Pakistan. The next youngest are also in Pakistan, from deposits formed in rivers. The next youngest are also in Pakistan, from estuary deposits. The next youngest are from multiple continents, but only in deposits from near-shore ocean environments. The next youngest are world-wide, in ocean deposits--and these guys actually look like whales. Here, the spatial distribution is informative, and fits the predictions based on the model: if a single population of land mammal gave rise to whales, then we predict that this population would have lived in one place (as populations tend to do). We'd predict that the first water-loving variants would be in the same region, in/near rivers (like their current cousins, hippos). We'd predict that they would not become world-wide in distribution until they developed really-good swimming ability. [But, for the fish-to-amphibian transition, I don't have a good prediction about spatial distribution. Maybe the fish could swim anywhere...]

So...what should the transitional fossils in this (hypothesized) series be like?

[rigadoon]

So we've got geological strata and sub-strata (which are interpreted as a temporal series, right?) and the number of fossils per area for each strata (which signify something about decline or not).

The evolutionary model, derived from the data, is that we have a continuous family lineage. By definition, this is a series. Like any family, grandparents give rise to parents, which give rise to children, which give rise to grandchildren, which give rise to great-grandchildren, etc. Here, the model is that this family went on for a very long time, and that the great-great-great...great-grandparents were fish; the great-great-great...great-grandchildren were amphibians. The changes in limb structure along this continuous lineage, according to the model, result from mutations in genes like Hox, shh, fgf, etc.

Pause here. The strata allow you to group fossils and order the groups. But how do you order the fossils within the groups? What is the within-strata ordering principle?

So, yes: this supposes a series. There should be intermediates. That is the hypothesis we'd like to test. To test an hypothesis, it is necessary to articulate what that hypothesis is (I did that above), and articulate the predictions the hypothesis makes. Then, one asks if those predictions are met. The general appearance of the intermediate fossils is one of those predictions.
... So...what should the transitional fossils in this (hypothesized) series be like?

If you answered my previous question, you have an ordering principle and so a method of arranging fossils in a series. Then finding an intermediate means inverting the ordering principle (which goes from fossils to ordered fossils) and deriving a method to go from ordered fossils to hypothesized intermediate fossils.

[Jose]

So we've got geological strata and sub-strata (which are interpreted as a temporal series, right?) and the number of fossils per area for each strata (which signify something about decline or not).

Basically, yes. BUT--the abundance of fossils was a relevant metric for the question that was asked specifically about the rate of decline of dinosaurs at the end of the Cretaceous. It isn't a relevant metric for the question of the intermediates in a continuous lineage. For one thing, the Hell Creek project looked at all dinosaur fossils, regardless of species. Needless to say, if you are counting contemporaneous tyrannosaurs and duckbills together, you're not dealing with an evolutionary series. With the lobefin-to-amphibian transition, you are asking about lineage, not about how many individuals there were of each species.

Pause here. The strata allow you to group fossils and order the groups. But how do you order the fossils within the groups? What is the within-strata ordering principle?

Fossils from the same stratum (ie, the same narrow band within a larger group of strata) are contemporaneous. No ordering is needed. After all, we don't try to make "an evolutionary series" of currently-living humans, trees, cockroaches, and malaria parasites. They're all living at the same time, and can't be each other's ancestors. From within a stratum, just like now, the individuals that you find (fossils for strata, living individuals for the present) inform you about the diversity present at that time. The diverse collection, whatever it may be, is only one snapshot in time.

The Fact of Evolution is revealed by the Fact that different shapshots from different times show us different life forms--different diversity at each timepoint.

If you answered my previous question, you have an ordering principle and so a method of arranging fossils in a series. Then finding an intermediate means inverting the ordering principle (which goes from fossils to ordered fossils) and deriving a method to go from ordered fossils to hypothesized intermediate fossils.

You anticipated a different answer than I gave . What we have is a bunch of collections of fossils, each from different times. Each collection is a sampling of the diversity from that time. The older collections preceded the younger collections in our time-series. Within each collection, however, there is no "order" because we're talking about things that lived at the same time.

Theoretically, if we were really lucky, it might be conceivable that we could collect zillions of fossils from the bottom-most stratum to the top-most stratum--let's say from A to Z--and thereby obtain a detailed view of the complete diversity of life throughout that time interval. Then, it would merely be a matter of matching the most-similar critters from strata immediately above and below, and we'd have a reasonable series. Then, we'd just look at 'em, and say "aha. This is what the intermediates look like--we know because we have them."

In real life, though, it's not like that. We might have a few fossils from time A, a few from time Z, and maybe one each from times D, H, R, and W. To find "intermediates," we'd look for more fossils--from the time periods from which we don't already have examples. Of course, we can only look in those rock formations that are exposed on the surface, and have had enough erosion to begin to separate the fossils from the surrounding rock, but not so much erosion as to destroy the fossils. Regrettably, the current erosion patterns that expose rock formations have no interest in providing us with ideal fossil-collection sites. So, in practice, this amounts to a lot of hiking and looking, with occasional lucky breaks.

So, if we find a fossil from time-period L, we know it's between H and R. If it's a tree fossil, we don't bother to consider it as an intermediate between lobefins and amphibians--it doesn't fit any of the predictions. If it's the right kind of critter, though, it might be an intermediate.

This is the type of situation that exists for most of these morphological transitions. There are some fossils, but not a fossil of everything that lived in that time interval. There are time periods from which we have not yet found fossils of this type of critter. So, here's the scenario: we have our fossil from time-period L. Is it an "intermediate form" between A and Z? Evolutionary biologists say "yes;" creationists say "no"--because they have made different predictions about what "intermediate forms" should be like. So, we're back to the question: what should intermediate forms be like?