What is evolutionary theory?

Continuing the discussion from Did We Have "Reptilian" Ancestors?:

I’m splitting this off as a new topic – partly to experiment with ways of using the board software to do that.

Please keep in mind that I am not a biologist. I hope some actual biologists will chime in and say where they disagree.

Darwin quite possibly did consider his ideas to be an hypothesis about origins. And Darwin made some mistakes, such as an over-emphasis on natural selection. This is understandable, since that was about all that he had at the time.

However, an hypothesis doesn’t get you very far. And, before long, biologists had taken this far beyond the level of an hypothesis. They saw evolution as a framework for studying biological change. In a way, Linnaeus started this with his classification system that particularly emphasized reproduction and reproductive organs as a way of sorting out the species. And once they knew of Mendel’s work on genetic, that was quickly incorporated into the study.

I’m inclined to see evolutionary theory as including reproduction, genetics, development (as in evo-devo), mutation and speciation. And I probably left out some of what should be included.

Frameworks are important to most science.

Philosophy of science tends to describe science as a system of descriptions that uses induction to advance the field. I mostly disagree with this. I see science as producing logical (and mathematical) models of aspects of the world. And the model allows mapping of real world phenomena into logic propositions. A theory often has many technical definitions which are part of the constructing of the model.

I also think Quine (the philosopher) made a mistake when he argued against the analytic/synthetic distinction. In a scientific theory, the technical definitions and part of the core of the theory are analytic propositions, while experimental science produces synthetic propositions (measurements, observations, etc).

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Elliot R. Sober’s Philosophy of Biology is in its 2nd edition. He has a number of articles and books worth reading.

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See here: Selected Papers - Elliott Sober

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I agree with this however natural selection gave an explanation of differences which appears critical for the theory.

What do you think has surfaced that adequately explains the differences between species?

What we see seems well explained by common descent. But I’m not sure what you are looking for.

Try comparing a bonsai tree with a natural growing tree. The growth of the bonsai tree was carefully controlled from when it was a seedling. Similarly, small changes that affect the development stage of an organism can result is quite large apparent changes in the resulting adult form.


This is where I see problems. According to Harshman common descent explains the similarities but not new features. I agree with this but then common descent is not an explanation of ancestry only similarities and differences we can attribute to reproduction.

I’m not understanding what you are saying there.

Thanks for asking for clarification.

For common descent to explain ancestry between reptiles and mammals it has to explain how the placenta which is a new feature emerged from reproduction. Emergence of a new features is not a claim of common descent according to Harshman.

Common descent only explains the similarities and differences we would expect from reproduction.

At this point Harshman is claiming common ancestry=common descent so there is still stuff to work out. In my opinion the only way to close this gap is if you can explain new features with reproduction (and the variation that comes with it) alone and there is little evidence supporting this claim. Reproduction would have to be able to create lots of novel FI and it does not appear to do that.

Granted. But I’m failing to see the relevance. I agree with @John_Harshman that common descent and common ancestry are about the same thing.

Yes, common descent is not intended to explain why new features arise. That’s related to genetics and mutations.


For the nth time, no it doesn’t. And “emerged from reproduction” seems meaningless, or at least I don’t know what meaning you’re trying to attach to it.

For the nth time, common descent explains the patttern of similarities and differences among species. It does not explain origins of the features themselves.

What is the difference? I’m pretty sure nobody knows what you’re trying to say here.


Mutations and selection explains new features, and those processes are part of the theory.

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I understand this and that is why it is a limited explanation.

All new features. Can mutation and selection build an eye?

Yes they can, and have. There’s considerable scientific literature readily available on the topic but I bet you never bothered to look.


What you mean, apparently, is that common descent explains the pattern of similarities and differences among species and nothing else. But that’s all it’s ever been claimed to explain. This is like criticizing Schrödinger’s equations for failing to explain the orbit of Venus. All explanations are limited; they’re limited to explaining relevant phenomena.

It appears that they can. But note that this has nothing to do with evidence for common descent.


I see no reason why mutation and selection could not build an eye. Do you have any reasons why evolution could not build an eye?

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Every explanation in science is limited to a subset of all observations.

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We agree here as I am yielding to your definition of common descent.

On what basis do you think that mutation and selection can build an eye? If we would through lots of discussion conclude mutation and selection is a poor explanation for the origin of the eye how do you think evolutionary theory would be impacted?

We agree.

This is where we disagree. I see mutation and selection as a terrible explanation for the eye.

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Why? What reasons can you offer besides your own ignorance based personal disbelief?