Fossil and Evolution

[articulett]

I'm just curious: when people say the fossil record is incomplete, what exactly do they mean? That we haven't yet dug up all the fossils that are in the ground available to us? That the fossil record doesn't show every species (or a sample of every population, or every individual) that ever lived?

In other words, what would it mean for the fossil record to be "complete"?

Yes...what would "complete" look like? And how are we supposed to get it when death degrades life forms over time? I liked Delphi's number analogy. And I think there were a lot of great answers that were hardly pat. I think I gave good links and answers.

Before DNA, we had to guess where animals fit based entirely on the phenotype of fossils we could find. With DNA we can see the actual changes and relatedness of individuals. It confirms evolution beautifully and opens the door to knew knowledge.

But phenotype does not directly correlate with how closely two animals are related; it's helpful...but if someone were to dig up dog skeletons, they might conclude they had a whole bunch of different species--whereas, many rodent species look similar, but are not the same species at all.

Here's another quirk about fossils and the like. Sometimes a single point mutation can cause a very noticeable skeletal change--achondroplasia (the most common form of dwarfism) is a good example. If achondroplasia helped a species that had it survive because, say, tall organisms were killed by tree snakes or something, then the fossil record would show a dramatic change with no inbetween forms--because achondroplasia is autosomal dominant. There wouldn't be skeletal examples of organisms inbetween achondroplastics and normal.

Albinism is similar, although it's recessive. An albino doesn't pass on (light colored genes)--only the normal pigment genes they carry and a recessive copy of a gene that can't translate the genes to produce pigment. An albino that carrys "dark" genes who mates with a non-albino that has "light' genes is likely to produce an animal darker than both parents.

So intermediary forms and fossils are helpful clues from a "macroevolution persepective, but visual clues and guesses leave out some of the finer details of the story. Especially since we've learned that a lot of genes are more like "basic floorplans" that can be modified via the environment the organism finds itself in. Just as blind people recruit the vision portions of the brain to enhance other senses--so, too, do emerging organisms utilize their genomes via adaptation.

By the way, I'm not insulted, Dr. A. There are many dishonest creationists who start threads with very similar hokey analogies and the "gaps in the fossil record" is a common part of the wedge strategy in regards to getting people to doubt evolution. Moreover, the OP admitted that he wasn't sure what he was asking. Also, people gave beautiful well written answers, and I thought it was insulting to dismiss them as pat. If they sounded simplistic it was because his candle analogy sounded so simplistic and wrong-headed that it left one with the impression that he didn't have much of a clue about evolution and might need some of the basics.

Moreover, if his question wasn't about explaining fossil gaps to creationists-- what do you think it was about? If I over-reacted it's only because I, like many here have been lead along this path before, and we all know it's a maddening experience to have someone carefully consider your question, give a detailed scientific explanation, and then have it dismissed as "pat" while repeating their favorite "flaw in evolution" theory again and again (shan't mention the ear worm).

 

[cbish]

......Given the the fragmentary nature of the fossil record, how does one explain how a succession of fossils with wide temporal separation constitutes a continuous progression?

The current fossil record does not appear to demonstrate a continuous and smooth progression; that however doesn't mean that evolution isn't smooth and continuous. I focussed on this fact, even attempting to provide an analogy the to way humans perceive continuous motion in their daily lives, because not only did it represent a deficit in my own understanding of evolution but it also seemed to provide a direct explanation of how evolution has progressed throughout the ages. It would be basically saying, "here are organism that existed long ago and there forms progress in a orderly fashion and, if scaled correctly, the changes appear continuous and, since evolution operates over large periods of time, the changes would appear continuous over what is called 'evolutionary time'." However, since the fossil evidence is too fragmentary to do that, I will just have to content myself with presenting the more, for lack of a better word, abstract genetic evidence..........

I think perhaps the problem is with the idea of 'continuity'. Are you familiar with Genetic Drift? Punctuated Equilibrium?

 

[JoeTheJuggler]

Generally, I think they mean that it isn't a comprehensive sample of all transitional forms.

I thought so.

But given the hit and miss nature of fossilization, surely a "complete" record isn't expected.

And every time the fossil of a transitional form is discovered, it creates 2 gaps in place of one. Obviously, they're not talking about a truly comprehensive sample of ALL forms. (Again, what would that even mean if not a record of every species that ever lived?)

mijo, I noticed that you're using the term "smooth" as well as continuous. Are you perhaps addressing punctuated equilibrium? My down and dirty characterization of PE: the notion that ecosystem tend towards homeostasis for some time until something disturbs the balance. So you get forms that persist more or less unchanged for a long time, and then periods of rapid change. Perhaps this is what you're seeing in the fossil record?

Even without punctuated equilibrium, I don't think anyone thinks forms necessarily change in smooth way (i.e. at a constant rate). Anyway I believe "smooth" and "continuous" describe two very different concepts.

By analogy: when you accelerate a car from 0 to 60mph it must be continuous, but it needn't be smooth at all. Smooth would be a constant rate of acceleration, where continuous just means that you can't change from one speed to another speed without going through the intervening speeds.

 

[geoman]

Well, you could start by explaining why, in your opening post, you refer to your degree in multiple scientific subjects, as a "Bachelor of 'Arts.'"

Hmmmmm?

Well, in mijo's possible defence, a few of those new-fangled degree-mill places give out BAs for science degrees. Ever heard of a place called Cambridge ?

 

[fls]

Given the the fragmentary nature of the fossil record, how does one explain how a succession of fossils with wide temporal separation constitutes a continuous progression?

The current fossil record does not appear to demonstrate a continuous and smooth progression; that however doesn't mean that evolution isn't smooth and continuous. I focussed on this fact, even attempting to provide an analogy the to way humans perceive continuous motion in their daily lives, because not only did it represent a deficit in my own understanding of evolution but it also seemed to provide a direct explanation of how evolution has progressed throughout the ages. It would be basically saying, "here are organism that existed long ago and there forms progress in a orderly fashion and, if scaled correctly, the changes appear continuous and, since evolution operates over large periods of time, the changes would appear continuous over what is called 'evolutionary time'." However, since the fossil evidence is too fragmentary to do that, I will just have to content myself with presenting the more, for lack of a better word, abstract genetic evidence.

My intent (which is completely irrelevant to the validity of any argument I might make) was never to refute evolution by exposing the fossil record as "gappy". Rather, I was wondering what kind of heuristic value can be derived from the fossil record given its incompleteness. Should discussion of the fossil record be avoided because of its "gappiness"? Or is there an intellectually honest way given the appearance of "discontinuity" in the fossil record?

I think the answer is that fossils are not a record of the continuous nature of evolution; fossils serve as a record of variety and progression. They say nothing about the mechanism, which is why they are justifiably dismissed as evidence of Natural Selection. We think that it's continuous based on other observations - our understanding of variation, genetics, inheritance, different forms of selection, etc. But if our observations of the present natural world revealed a different mechanism by which we see a variety of organisms with a progression in the types that we see (for example - that life arises spontaneously from different inanimate materials, but the nature of the organisms already present conditions the material to generate similar forms), then we would have a different explanation for the mechanism that generated that same fossil record.

Whether or not there are gaps is irrelevant to what we are asking of the fossil record, and I think discussion of the gappiness is a red herring.

Linda

 

[mijopaalmc]

Well, in mijo's possible defence, a few of those new-fangled degree-mill places give out BAs for science degrees. Ever heard of a place called Cambridge ?

In the case of Whitman College I think the issue is more legal than anything else. After the college was originally rechartered from being a Methodist seminary (it is no longer in anyway affiliated with the Methodist Church and hasn't been since 1859), its new charter only granted it the ability to grant BAs. I don't know why they haven't made a move to gain the ability to grant BSs, especially since the sciences have always been fairly popular with large well-staffed departments.

If there is some genuine interest in my relatively limited credentials, the requirements for my degree can be found in the corse catalog along with the description of the required courses. The file is rather large pdf which has to be downloaded before you can view it.

 

[articulett]

In the case of Whitman College I think the issue is more legal than anything else. After the college was originally rechartered from being a Methodist seminary (it is no longer in anyway affiliated with the Methodist Church and hasn't been since 1859), its new charter only granted it the ability to grant BAs. I don't know why they haven't made a move to gain the ability to grant BSs, especially since the sciences have always been fairly popular with large well-staffed departments.

If there is some genuine interest in my relatively limited credentials, the requirements for my degree can be found in the corse catalog along with the description of the required courses. The file is rather large pdf which has to be downloaded before you can view it.

I don't care so much about the degree. I want to know what you think of the explanations. Delphi_Ote's number line example was very simple, and right on target. Moreover, I don't think most scientists are seeing the discontinuity and gaps that creationists may believe they are. There is so much more data coming in all the time.

If a creationist brings up discontinuity, I think it might be a good idea to ask them exactly what they mean as JoetheJuggler asked you--

The fossil evidence were the first big pieces of the puzzle in regards to evolution--but DNA is what confirms it in stunning clarity. We have lots to learn, but there is no doubt we are on the right path--even if we never discovered another fossil--

As our tools get better and more refined in science, the clearer the picture becomes. I'm not even sure if creationists know what they are talking about when they say gaps in the fossil record.

 

[ponderingturtle]

Well, in mijo's possible defence, a few of those new-fangled degree-mill places give out BAs for science degrees. Ever heard of a place called Cambridge ?

There is no universal standards of what BA vs BS means. For physics at the school I went to, it was BA needed quantum mechanics and an elective vs Advanced Mechanics and either Electric circuit analysis or Digital circuit analysis.

 

[Dr Adequate]

Rather, I was wondering what kind of heuristic value can be derived from the fossil record given its incompleteness. Should discussion of the fossil record be avoided because of its "gappiness"? Or is there an intellectually honest way given the appearance of "discontinuity" in the fossil record?

But there is no appearance of discontinuity and more than there's an appearance of continuity. The fossil record is discontinuous, but that's just the fossil record for you: it doesn't suggest that the history of evolution is discontinuous any more than the photos of the lava lamp would. You can say that the photographs appear to be discontinuous, but you can't say, based on that, that the lava lamp appears to be discontinuous.

On the contrary, only a continuous physical model of the lava lamp allows us to explain and predict the observations and is consistent with the laws of nature. The same might be said of evolution. Only the continuous theory, for example, allowed the prediction of such creatures as Tiktaalik. Abandon continuity, and no-one could have even guessed that it existed or known where to find it.

The fossils are evidence of continuity not because they are themselves continuous, but because they are exactly what we'd expect to see if evolution was continuous and fossilisation was rare (which it is).

 

[JJM]

There is an interesting article about filling the gaps in evolution:
The mammals that conquered the seas: Dawn breaks over the Tethys Sea, 48 million years ago, and the blue-green water sparkles with the day's first light. But for one small mammal, this new day will end almost as soon as it has started.(origin of whales). Kate Wong.
Scientific American 286.5 (May 2002): p70(10).

As recently as the early 1980s we had modern whales, and land animals that shared skeletal features. Creationists had a field day with the hypothesis of evolution being offered with no intermediate forms. But- where do you look for intermediate forms for an animal that lived in the sea? It turns out that the lowlands in Asia and North Africa had many answers. What is now the northern Sahara Desert was once a shallow sea!

As for the BA/BS question- educational philosophy is quite variable. You have technical schools that concentrate on the BS, and Liberal Arts schools that focus on the BA. I briefly attended a school that offered both. The BS degree (in chemistry) required several additional science courses, such as a third semester each in Organic and Physical Chemistries, and Calculus.

 

[mijopaalmc]

I think the answer is that fossils are not a record of the continuous nature of evolution; fossils serve as a record of variety and progression. They say nothing about the mechanism, which is why they are justifiably dismissed as evidence of Natural Selection. We think that it's continuous based on other observations - our understanding of variation, genetics, inheritance, different forms of selection, etc. But if our observations of the present natural world revealed a different mechanism by which we see a variety of organisms with a progression in the types that we see (for example - that life arises spontaneously from different inanimate materials, but the nature of the organisms already present conditions the material to generate similar forms), then we would have a different explanation for the mechanism that generated that same fossil record.

Whether or not there are gaps is irrelevant to what we are asking of the fossil record, and I think discussion of the gappiness is a red herring.

Linda

I think that this is the most clear answer that I have received. My problem most probably arose in that I was trying to directly answer an irrelevant question. If it can be agreed that the fossil record is not in and of itself evidence of natural selection, as Linda suggests, then it seems that it is missing a vital component to make it a strong (I know this is a vague term) example of evolution. This is not to say that the fossil record does not constitute an example of evolution at all. Nevertheless, since the succession of fossils lacks an empirical demonstration of natural selection, one of the most important mechanisms of evolution (and, from what I understand of the philosophy of science, one of the defining characteristics of science is that it offers a mechanistic explanation for empirical phenomena), it is not as strong an example of evolution as one that contains demonstration of more mechanisms that have been defined to be part of evolution.

I was looking for a less hand-wavy way of addressing the "gappiness" of the fossil record and since it appears that it is actually irrelevant to evolution (if I am accurately reading what Linda is saying), it seems that explaining that you can actually see evolution happening before your eyes today is a much more fruitful of demonstrating that evolution exists.

I guess probably a better question would be:

In the sum total of all our evidence for evolution, how does the fossil record fit?

Forgive me if I am repeating myself; I am just thinking out loud right now.

 

[Dr Adequate]

Nevertheless, since the succession of fossils lacks an empirical demonstration of natural selection ...

On the contrary.

The law of natural selection places strict constraints on what we can and can't see in the fossil record. Every adaptation has to be immediately useful, or perish. For example, you can't have flowering plants before you have pollinating insects, because things can't evolve just to be pretty. Nor can a structure develop in such a way that it's only useful when it's finished, because natural selection can't look ahead.

 

[cbish]

But there is no appearance of discontinuity and more than there's an appearance of continuity. The fossil record is discontinuous, but that's just the fossil record for you: it doesn't suggest that the history of evolution is discontinuous any more than the photos of the lava lamp would. You can say that the photographs appear to be discontinuous, but you can't say, based on that, that the lava lamp appears to be discontinuous.

On the contrary, only a continuous physical model of the lava lamp allows us to explain and predict the observations and is consistent with the laws of nature. The same might be said of evolution. Only the continuous theory, for example, allowed the prediction of such creatures as Tiktaalik. Abandon continuity, and no-one could have even guessed that it existed or known where to find it.

The fossils are evidence of continuity not because they are themselves continuous, but because they are exactly what we'd expect to see if evolution was continuous and fossilisation was rare (which it is).

Well said! Even if you are pissed at me!

 

[cbish]

I guess probably a better question would be:

In the sum total of all our evidence for evolution, how does the fossil record fit?

This is a good question. As mentioned before, because of an incomplete record, it may be the weakest.

I'm still curious about your ideas on 'continuity'. Are the people you speak with assuming speciation according to Adaptive Radiation? If so, this is why Eldridge & Gould proposed their theories in the lat 1970's. It fit observation better.

 

[mijopaalmc]

Dr Adequate, how did you read Linda's comment in #125?

I was riffing off of her. It is possible, maybe even highly likely, that I misunderstood her, but I thought that the gist of her post was that the fossil record provides rather weak evidence for the mechanisms of natural selection.

 

[fishbob]

. . . . I thought that the gist of her post was that the fossil record provides rather weak evidence for the mechanisms of natural selection.

Whether the fossil record provides an explanation for the mechanisms of natural selection is an entirely different question than whether the fossil record provides evidence for natural selection.
Which one do you want to know about?

 

[siqr]

...I am simply asking whether the evidence we claim is provided by fossils is really as strong as we would like to think it is.

The Origin of Species, chapter 10, "On The Geological Succession of Organic Beings" summarizes the reasons why the fossil record demonstrates evolution.

1. Species are continuously created. But these new species appear only slowly. This is what is expected under evolution by natural selection.

2. Some species persist through the geological record; others go extinct, as expected under the theory of natural selection. [this argues against theories of successive, regular extinction and creation]

3. Throughout the fossil record, new species resemble previous species

4. The more ancient a species, the more different it is.

5. The more ancient a species, the more "intermediate" it is. i.e., ancient species tend to fall between distinct groups of modern species. The more ancient the species, the more distinct modern groups it links. The totality of fossil species blends the distinct genuses we have today.

6. Once a species disappears from the fossil record, it does not reappear -- as expected by the theory of evolution by natural selection

7. When we consider groups of species that closely resemble each other (genuses, families) their existence in the fossil record is continuous. [This is necessary if species arise via evolution. If the group goes extinct, no new species in that group can ever again emerge.]

8. When a new group of species appears in the fossil record, initially there are only a few species representing the group. Gradually the number of species increases. This is explicable under evolution by natural selection. If species were created by some other means, why don't we see a group filled with numerous species appear all at once?

9. Lastly, and most tellingly: the fauna of each continent tends to be distinct from other continents. But the most recent fossil beds of each continent comprise species which closely resemble those living there today.

That chapter's fascinating reading. I'd post a link, but the forum software won't let me :-( you can find it at

literature.org/authors/darwin-charles/the-origin-of-species/chapter-10.html

 

[Ichneumonwasp]

the fossil record provides rather weak evidence for the mechanisms of natural selection.

I would disagree with the assessment "rather weak" as well. Even as the weakest link (I'm not sure that is even the case), the fossil record is still overwhelmingly strong evidence for evolution by means of natural selection.

 

[delphi_ote]

I thought that the gist of her post was that the fossil record provides rather weak evidence for the mechanisms of natural selection.

The mummy of a dead critter doesn't directly give us evidence of the enviornmental stresses on its species. So no, we can't reach into the fossil record, grab natural selection by the neck, and hold it up for all to see.

But as Dr. A and Darwin (via siqr's excellent post) pointed out, we can indirectly infer these things from the fossil record. That evidence is damn good. Make sure you really think about both of those posts. There's a subtle (but beautifully elegant) logic to this argument.

 

[articulett]

One of the problems both proponents and opponents of evolutionary theory is the fact that the jumps between species are so large - obviously the changes take place over millennia, which is [start ID mode] why don't chimpanzees and bonobos give birth to more highly-evolved species any longer?[/close ID mode]

The enormous jumps aren't actually enormous at all, it's simply a lack of fossils make it appear so. The number of fossils is a minute fraction of all the animals. What evolutionary scientists are trying to do with fossils is akin to trying to tell what a 1000 piece jigsaw puzzle shows a picture of with only 16 pieces.

They are evolving too, you silly. Evolution is a long term process and the population of other primates is small--but keep up--
http://news.nationalgeographic.com/news/2007/03/070307-bonobos-video.html
http://www.sciencedaily.com/releases/2007/02/070222155719.htm
http://www.johnhawks.net/weblog/topics/minds/culture/social_learning_culture_2006.w

Evolution doesn't happen on an observable timescale--and what we think of as evolved isn't necessarily the most adaptive for every organism. Evolution is only what traits enhance a species reproductive success over those of competitors. Intelligence isn't necessarily the best survival strategy. It has worked for humans...but it may be our undoing as well. Beetles have been around longer, and so many different types have evolved, continue to evolve, and die out.