@JamesPlaskett Dialogue of the deaf, pt.2: points of difference

When I chose to open this debate, I thought it might be interesting to find the point of difference about cytochrome c, which I’ve always thought of as an open-and-shut case as proof of evolution.  However, it seems we now have too many points of difference to be discussed easily.  I wanted to compile the list, if only to clarify my own understanding of the ground.

I feel a despair about arguing on too many fronts at once; I don’t have time to do the research required to take all your arguments seriously.  So, I suggest, until we decide what is the point of difference about the molecular evidence, then I’m happy to let these other points languish undiscussed for the moment, with an option on raising them later if that seems mutually interesting.

Cytochrome c / molecular evidence See comment on previous blog post. See comment on previous blog post.

The most natural interpretation of the molecular evidence is to say that it confirms evolution has happened and proceeded in the pattern of a branching bush, a conclusion supported by much other evidence (geographic, morphological etc.).  I think the argument you are citing to dispute this is not only bogus, it has been abandoned by its inventor, Denton.  Comments invited.

Natural selection Unlikely! Inevitable!It seems to be that if you have (1) inherited variations and (2) differential survival (breeding success), you will get (3) evolutionary change.
Observed speciation NO speciation event yet observed. Cited instances of speciation are ‘nonsense’. I think you can only maintain that position by
(a) excluding speciation by other than natural selection (polyploidy),
(b) insisting on the 1937 definition of species that includes the criterion ‘physiologically incapable’ (which not even its originator stuck to), and
(c) concluding that lions and tigers (together with leopards and jaguars) are the same species.

I think that is tortuous, and to dismiss all the available evidence as ‘nonsense’ is too harsh.  Taken together, the examples collected by Boxhorn in 1995 seem to me to be pretty good evidence that evolution (by natural selection) could result in new species, even by the 1937 criteria – evidence, I’d say, beyond reasonable doubt. If we haven’t yet quite seen the whole process through to complete physiological incapability – and some of those examples are pretty close – I think the idea is holding up well. (Unreasonable doubt = I need CCTV footage of the whole burglary before I convict a burglar.)

If you don’t insist on the 1937 definition – and I think no living biologist does, as they would like to be able to say that lions and tigers (as well as ivy and Fatsia) are different species – then the evidence that speciation has been observed is abundant. It is the differences between lions and tigers that I want natural selection to explain.

Complex structures Evolution of complex structures is too unlikely (e.g. the eye as cited by Grasse) Taking what is generally regarded as a useful test case, the evolution of the eye, and making some conservative assumptions (1% change in proportion arises by mutation, mutations happen at observed rates, 1829 1% steps are required, modest selection pressure applies), the maths suggest that there has been time for a complex eye to have evolved from scratch – time indeed, for it to evolve, not just once, but 1500 times in a row (Nilssen and Pelger 1994).

If you want to disbelieve, I can’t stop you, but if you want to disagree, you may have to roll your sleeves up and do some maths.  (I confess the maths may be beyond me.)

Useful mutations Useful mutations don’t happen (or are too unlikely, I’m not sure which claim you are making)’NO spontaneous beneficial mutation’ Examples:
Bacteria keep evolving resistance to antibiotics, clearly beneficial.
Lenski (2008) showed (repeated) evolution of capacity to use citrate in experiments with E.coli.
Black form of peppered moth was useful, then wasn’t.

If it’s an argument about probability, then I think I’m going to say again that expressions of incredulity are expressions only of belief and not a contribution to the argument.

Complex life cycles Evolution by natural selection can’t account for these (e.g. tadpole/frog, caterpillar/butterfly – my examples) This is an unusual and possibly original argument, but I don’t feel I’ve got it yet.  I don’t see why natural selection cannot pull the juvenile and adult stages in different directions, either simultaneously or at different times.
Convergent evolution Evolution by natural selection can’t account for these, (e.g. European placental mole and Australian marsupial mole – my example). Just as above: this is an unusual and possibly original argument, but I don’t feel I’ve got it either.  I regard the appearance of parallel adaptations more as evidence for evolution than as an argument against it.
Natural selection Evolution by natural selection is too slow

(I think you are making this point, by invoking the ‘Crick Statistical Fallacy’ and stating “@RichardMilton and I dispute that the supposition of parallel processing´, in genes simultaneously improving is realistic.”)

If you allow for selection pressures to act in a population on more than one gene at once (e.g. bigger and stronger or bigger and darker), then there is plenty of time (Wilf & Ewens 2010).

Again, I think that if you want to dispute with any seriousness since this 2010 paper, you have to roll your sleeves up and do some maths.[I forget who made the ‘too slow’ point first, but pretty sure it wasn’t Crick.  (Fisher?)]

Nature of science ‘Probably’ is not good enough ‘Probably’ is as good as you get; certainty is for mathematicians (and theologians).I wouldn’t offer anything in science as absolutely ‘certain’ or ‘indisputable’.  (We were pretty sure about Newtonian mechanics, but that turned out to be at best a useful approximation and seriously flawed if you want your GPS to work.)  I would offer natural selection as the best current scientific explanation we have for most* examples of adaptation and speciation.

* Genetic drift is the best explanation of the cytochrome c ‘bush’, sexual selection is the best explanation of the peacock’s tail, and so on.



Filed under science & natural history

2 responses to “@JamesPlaskett Dialogue of the deaf, pt.2: points of difference

  1. Pingback: Four comments on DNA and evolution, with references | minorityattack

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