Transitional forms in human evolution

How is that the takeaway?

Let’s say you have a family legend about a great-great-grandpa Bob. You know that the family name is O’Leary and you know what town the family came from. You visit that town, and in the historical records/cemetery, you find not one but five Robert O’Learys, some of them named Jr, Sr, or III. Some of them even have pictures that sort of resemble your family. What can you conclude? That your quest was doomed from the start? Or that you found some people closely related to, if not on, your direct line of descent? You may never know which one was the Bob in question, but you still know more than you started with, and that’s not meaningless.


Taking Tiktaalik as an example, if that can be regarded as transitional then it would appear that the “transitional” fossil doesn’t even need to predate the descendant, nor can it be shown that they descended from a common ancestor. Basically you can take any fossil that is intermediate in form regardless or relatedness or time frame.

Un less you are claiming that the “transitional” fossil is in the supposed line of descent then it has no evidentiary value for supporting the claim.

Hi Chris,

Tiktaalik is definitely transitional between lobe-finned fishes and amphibians. It is intermediate both in form and time.

Are you focusing on the fact that at least one other transitional form appeared a bit earlier than Tiktaalik? That does not disqualify its classification as a transitional form.


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This is not an area of expertise at all for me, but one that I’ve been reading on for a year or so now. I think that from a creationist or ID perspective, you are correct, Chris. We tend to think of species as static pictures that have arrived and are fixed in time. Transitional species are the breadcrumbs that lead from S1 to S2.

In actuality, species are not static pictures, but are more like movies, flowing through time. Everything, is–technically-a transitional form, because it is a form in transition. The species is changing over time, and sometimes becoming a new species. This is how I have grown to understand it anyhow. I am happy to stand corrected, however.


Here is a possible tweak or improvement in your analogy (from another lay person). Even the phrase “becoming a new species” might itself be freighted with misconception, as it may cultivate the impression that even among this “flow of S1 to S2” there are definite stop points of “arrival” (species) as if, instead of a steady river, we have a string of connected lakes. It would be true enough that there must exist definite points of speciation, but these would be more like forks in a river where the stream flow goes either one way or another without ever rejoining.


Yes, very good point. I think that this would be helpful for @aarceng as well. Thanks Mervin for this clarification!

Tetrapod footprints predate Tiktaalik by millions of years. It might be intermediate in form but certainly not in time. Neither can it be shown that it was in a line of descent from fish to tetrapod.

I said above in #36 that

So unless the “transitional fossils” are on that line of anagenesis then they actually have little evidentiary value. Unless you start with the assumption that both H. sapiens and Australopiths have the same common ancestor you can’t even claim that Australopiths are transitional through sharing a common ancestor. It becomes a circular argument.

I would like to explore the meaning of “little evidentiary value,” if we can dig a little deeper into that.

The biggest assumption that evolutionists are making here is that any given fossil creature had ancestors similar in form to what we see. Does any brand of creationist actually disagree with that?

Do they have an alternative model that makes more sense—like that God created chimps and gorillas and australopiths and Homo in Africa all separately, and they just happen to have looked a lot like each other on the edges because there aren’t that many different forms God could have used, really?

What kind of evidentiary value would a direct ancestor give us that is not easily surmised from its descendants a million years later?


You keep making the same objection and getting the same correction. Below I offer you a version of the correction specific to the issue we are discussing. I will try to offer enough detail so you can see where your misunderstanding of the theory of evolution lies.

You are drawing a conclusion based implicitly on the assumption that there was one and only one line of ancestry connecting lobe-finned fishes (LFFs) to amphibians. This is not at all what the theory of evolution proposes. There were thousands of populations / species of LFFs 410mya and thousands of populations/ species of amphibians 320mya. There were also common selection pressures at work (e.g., availability of food on land) that drove the process during the transition. It is completely expected that different populations would be at different stages of the transition at different times. Thus it is completely unremarkable that Tiktaalik was not the first transitional species between LFFs and amphibians.

To give an example from modern times, the fact that humans are farther along in language capability does not mean that birds, dolphins, and whales have not evolved some language capability.

Note also that not all LFFs participated in that transition. We can find LFFs today, albeit not identical to the ones that lived 400mya. Similarly not all amphibian populations participated in the transition to reptiles, albeit the amphibians we see today are not identical to the ones that lived 320mya.

You are under no obligation to accept the theory of evolution, Chris. You might find it useful to understand the theory better, however.

I am not sure why you are disagreeing with paleontologists about this, Chris. They find its morphology to be intermediate in many ways between LFFs and amphibians.


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I have to second Chris’ thoughts here…

As there must be more to it than this…

else I could say that the salmon I had for supper last night could be a listed as a transitional form between a sponge and a stegosaurus, as it has some traits of the former (breathing from water) and the latter (is a vertebrate)?

If last night’s supper qualifies as a “transitional fossil” of sorts between sponges and dinosaurs, then I’d have to agree with Chris that the term seems to have been stretched so far as to have lost any significant meaning.

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Or why shouldn’t a Reindeer be considered transitional between a Dik Dik and an Irish Elk.

Actually, now that I look at them, I think it really could be true.

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Well, isn’t it? Granted, there are a lot more steps we know of between sponges and stegosaurus, but the evolutionary path definitely went through fish, just not salmon specifically.

Lampreys and hagfish are considered transitional between fish and non-vertebrates, iirc, and sponges are transitional between early fungi-animal ancestors and the rest of the animal kingdom.

When biologists say everything (or everything that didn’t go extinct anyway) is transitional, it’s not exaggeration.

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It occurs to me that “transitional” only has meaning within the evolutionary framework. Outside of that , it is relatively meaningless. Thus, calling the salmon you had for dinner “transitional” is about the same as calling a stegosaurus fossil “delicious.” Even if you find a little soft tissue.:wink:
Within evolution, it is still a perfectly good word.
It also is sort of like the word "inerrant " in some respects. Useful if defined but having such broad meaning to different people that it lacks meaning if not defined.

If one starts the discussion by assuming the evolutionary process, then yes, fish in general are part of that presumed pathway.

But to people who are dubious of the evolutionary path itself, making these kind of claims is, to borrow Chris’s word, not “evidentiary.”

If one proposes an evolutionary pathway from A, though B, arriving at C, skeptics seem to object, “but we have no fossils of B.” B is a missing link, and to skeptics, this casts doubt on the particular suggestion.

No to worry, assures the proponents. We might not have evidence of B, but we have “D”, that also has traits of both A and C.

But, says the skeptic, “D” is dated such that it never existed until well after both A and C. Therefore it can’t be evidence of “transition” between A and C.

Not to worry, assures the proponents. We can assume not only that there was a “B”, But we can also assume that “D” is descended from “B”. Thus D is in fact still evidence of transition between A and C.

And in that way the salmon down at our local supermarket can become “evidentiary proof” that sponges evolved into dinosaurs in a process that ended 100 million years ago!

So yes, for someone already convinced of the overall Darwinian tree of life, these sorts of anachronistic “transitional” fossils fit the theory. I.e., they are not inconsistent with it.

But to serve as “proof”, or evidence, for a skeptic like myself, they simply rely on too many assumptions.

On another note…

My understanding of creationist, as well as the perspective of lots of others who are skeptics of evolution who are hardly creationists (like Behe), is that God may well have started with a particular original, with the potential for genetic variety (either through minor mutation, “devolution”, and/or by front-loading genetic variety into the original life forms), and all these varieties of species descended with modification from original ancestors into the various varieties we witness.

That is certainly what the apostles seemed to understand it at least one sense… they certainly were not blind to notice there were different traits among various human tribes and nations throughout the Roman world…but they seemed to believe this variety came because he made from one man every nation of mankind to live on all the face of the earth.

Hi Daniel,

You have a fundamental misunderstanding of the evolutionary biology here.

Salmon is not a transitional form for anything because it is a leaf node in the chordate tree structure. I.e., the salmon population did not exist 20mya, it exists today. Thus it cannot be a transitional form under the definition we have been using.

Likewise, our friend @aarceng’s ruminations on deer, elk, etc. are not apropos because they are all leaf populations on the chordate tree.

On the other hand, Tiktaalik inhabits a branch on the tree that is intermediate in form and time between the lobe-finned fishes and amphibians. Thus it is a transitional species.

What paleontologists are unsure of is how far the branching structure continued after Tiktaalik. It might have continued down to the early amphibians and perhaps beyond. Or it might have been cut off prior to 320mya. Moreover, Tiktaalik was assuredly not the only transitional species between lobe-finned fishes and early amphibians. Several branching structures parallel to Tiktaalik’s could have led to the early amphibians. We simply have insufficient information at this time to make definitive declarations about these fine details.

The information is sufficient, however, to show that transitions consistent with evolution were occurring in the predicted time frame between early lobe-finned fishes and early amphibians.

Chris Falter


You don’t have to convince me. I was just using Christy’s definition that transitional fossils are “Fossils that have traits in common with a modern form and an ancestor form,” and drawing that to its logical conclusion… one which Lynn at least seemed to concur with. (“Well, isn’t it?”)

I for one think any definition of “transitional fossil” that would allow a modern salmon to meet that standard for 100 million year old creatures is woefully lacking.

Well, then, I would have to say that Christy and Lynn used the definition in an unconventional way. :grinning:

Neither Lynn nor I were proposing some kind of technical definition for all time, we were explaining our use of a term in a specific conversation about a specific diagram. You can’t take the description out of the context (which was describing organisms that are part of the same evolutionary “bush,” like the image we were discussing) and apply it somehow universally. Most things do become absurd when you ignore the context people are using to communicate. I don’t feel all that inclined to defend what we said. I think we made sense in the context.

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