Is Evolution Reversible

Hi doc, and welcome to the fray. Only if they lose their advantage, otherwise selection will continue to favor them. Conditions can change, such that advantage and disadvantage oscillate with ecological conditions, especially ones that fluctuate in a cyclic manner over cycle times greater than generation times. Here's an example of this kind of thing happening:Newsroom - The Source - Washington University in St. Louis

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Walking sticks regained flight after 50 million years of winglessness
Maxwell and his collaborators at Brigham Young University discovered that some species lost the ability to fly at one point of their evolution and then re-evolved it 50 million years later.

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And it is not just ONE such instance, but several. See Figure 1 from Nature 421, 264 - 267 (16 January 2003); doi:10.1038/nature01313 (reproduced below)Walkingstick insects originally started out as wingless insects (blue at start and top row). That diversified.And some of them gained wings (red). And diversified.And some of them lost wings (blue again). And diversified.And one of those gained wings again (Lapaphus parakensis, below, red again).Is that what you are looking for? As long as the mutations are retained in the population, then the variation in frequency of alleles by natural selection can favor one set of alleles in one condition and another set of alleles in a second condition, so it is entirely possible for the population to shift back and forth between existing and available variations in an oscillating ecology. An easy example of just this happening is the peppered moth, as described on Peppered Moths and Natural Selection, where we have two varieties of the moth:

Biston betularia typica (the light color version) and

Biston betularia carbonaria (the dark color version)

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B.b.typica was the predominant variety before the industrial revolution, during the industrial revolution's dirtiest times the proportions of the two populations shifted so that B.b.caronaria became the predominant form. Then the industries cleaned up and B.b.typica returned as the predominant variety.

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This does represent the change in hereditary traits in populations from generation to generation -- evolution in it's basic form, and what is usually meant by "microevolution" by biologists and creationists (something they agree on???).

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Message 1

... but is macro-evolution reversible?

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This depends on what you mean by "macro-evolution" and what you mean by reverse.

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As Mr. Jack noted dolphins are mammals that have become fish-like. They have "reversed" to a marine organism from a land organism.

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But if you mean "macro-evolution" as the division of species into multiple species (speciation) and then the development of relationship groups -- genera, families, etc -- the reversal of divisions of species into different categories of species (what biologists mean by "macro-evolution"), then no, that will never happen. Once the division of a parent species into reproductively isolated daughter populations has occurred that division cannot be undone.

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Enjoy.

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Hi doc, All of the species and the right side of the diagram are in existence today, but what the diagram does not show you is whether there was what would be called "orbitrary speciation" along any of those legs. What you see are the speciation divisions of populations and the final results 50k 50 million years later. Thus the top line could be just as recently evolved as the others, just that all the mommy and daddy species were wingless. Ah, but "wing" or "wingless" is not necessarily a single gene, nor is just a matter of turning it on or off. What we are likely seeing is the loss and re-evolution of parts of the whole wing formation process. This process may in fact be broken in different places for different species.You can turn a feature off by blocking or removing any part of the development critical to the formation of wings, and this would likely leave you with the same original feature that the wings evolved from, plus some genes inherited while winged that are not removed. Thus if a new by-pass is evolved to get around the blocked or removed part it would allow necessarily similar wings to evolve - it would be preadapted to form similar wings.This would be similar to the "Irreducible Complexity" refuting experiment done with E.coli (see Ken Miller "A True Acid Test") where an element crucial to the metabolism of lactose was removed from a subsystem, and a new set of elements evolved to replace the broken subsystem allowing the whole metabolism system to function again. How much is "significantly different"?Would it not still be working from the same basic features that were there when the wings first evolved? If I remove a sprinkler from the end of my hose I am still capable of watering the lawn, and I can put another sprinkler on the same hose.If a bat lost the bat wing, would it not still have a hand\paw with finger bones that can evolve back to support a skin membrane?Is the membrane pattern of the colugo significantly different from a bat?Does not convergent evolution answer this question best then? If a possum and a squirrel can evolve into such similar critters from widely divergent backgrounds and many eons from a common ancestor, then is it not possible that the same ecological niche can drive evolution to repeat a similar solution? The switching on and off -- if that is indeed what was happening -- is still caused by mutations, so all of it is mutations.Enjoy.Edited by RAZD, : correction

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Hi Doc, Well you could read the article and find out, but thanks for the correction:Newsroom - The Source - Washington University in St. Louis

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Maxwell and his collaborators at Brigham Young University discovered that some species lost the ability to fly at one point of their evolution and then re-evolved it 50 million years later. Moreover, the data indicate it is likely that re-evolution of these species may have occurred more than once.

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It's actually over a longer period of time, as the 50 million years applies to one instance. Curiously, you are still left with evolving the ON switch and the OFF switch and the ON switch and the OFF switch ... Agreed. It is much more likely to find other steps to reach the same result. That the vein patterns in the wings are the same means that the vein pattern is not lost, ... but then this is the vein pattern in the part when it is NOT a wing as well as when it IS a wing. But the question remains: if the wing is turned OFF by one mutation, and then later is turned ON, then is this a new mutation of a new ON switch, or is this a new mutation that reverses the mutation that turns the wing OFF? It is entirely possible that both could occur. Selection for improved survival and reproductive success in an environment where having wings is beneficial would favor their use. Selection for improved survival and reproduction in an environment where having wings is detrimental would favor their absence. Seeing as the analogy was not about how sprinklers evolve, this is a non-sequitur. The point is (was) that any sprinkler will assist in watering the lawn so that I don't have to stand there with my thumb on the end.Do you want to discuss how a sprinkler could evolve? Or do you want to admit that your "almost impossible" is just your argument from incredulity, coupled with a lack of imagination?Enjoy.

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we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.

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