But accommodating the inheritance part of it isn’t the issue, I think. Darwin would have said that the characteristics of species evolve through differences in reproductive success, and epigenetics provides for evolution without necessarily relying on reproductive success differences. That there be any reproduction at all is sufficient to change characteristics for a few generations.
Thus, it’s a kind of evolution other than Darwin’s. Which is not to say that Darwin’s kind does not occur or even isn’t the most important, but only to say that Darwin’s kind isn’t the only kind.
Or do I miss your point?
Reproductive success determines who gets to have their heritable traits continue. Epigenetics works the same way. Darwin didn’t know what the underlying mechanism of inheritance was. Epigenetics is no different. It does open up the broader realm of ‘mutation’ to more factors though. We still don’t know how all the factors in inheritance work, but we do know it’s not by magic, which is what Darwin was trying to prove.
Well, I am not sure I understand your point. How do you think that epigenetic effects amount to evolution? Yes, it has been shown that environmental conditions can have epigenetic effects a generation or two down the line, but I do not think that that itself amounts to evolution.
I admit I am far from confident that I fully understand the issues here, but so far as I can see, when these epigenetic effects manifest themselves, the genome (or the frequency of certain genes in the population, or whatever) hasn’t really been changed, just the way that certain genes are expressed in subsequent generations, and later changes in environmental conditions may reverse the first set of epigenetic effects, or cause others, but all without necessarily changing the genome or gene frequencies. There are, presumably, genes behind the capacity to display particular epigenetic effects, and they have not (or not necessarily) changed. Epigenetic effects may complicate what we take to be the unit of selection (because it may be that in some cases what is selected for is only manifested over multiple generations), but long term evolution is still going to depend on selection of genes. That is to say, being susceptible to certain epigenetic effects may confer a survival (or reproductive) advantage upon a population, and if so, the genes underlying that susceptibility will be selected for. This is still evolution by natural selection.
ETA: TriPolar has probably made the point more clearly than I managed to.
Aliens?
Yes. As I said above, the phrase “survival of the fittest” came from Herbert Spenser’
Descent with modification and natural selection are different things. Darwin referred to both, and his mechanism for evolution depends on both processes working together in concert. However, unlike natural selection, descent with modification wasn’t a particularly revolutionary idea. It was more just a formulation of common sense. After all, people had always known that children resemble their parents, but not exactly.
Well, that depends what you mean by Lamarkianism. It is not inconsistent with Lamark’s idea of inheritance of acquired characteristics, but the was more to Lamark’s actual theory than that, and other key aspects of Lamark’s theory are incompatible with Darwinian theory. For instance, Lamark thought that species (or, more accurately, lineages) never went extinct, but just evolved into different forms, so that, for instance, the direct descendants of T. Rex and of trilobites are still with us. Darwin’s theory, by contrast, depends on extinction as a mechanism. If unsuccessful forms did not die out, there would be no speciation.
Actually, Avery is the person who first clearly demonstrated, in the 1940s, that it is the DNA in the chromosomes, rather than the protein, that carries the genetic information. (Although hardly anyone believed him at the time.) I think it was known that the genetic information is in the chromosomes well before that. However, I agree with the thrust of what you are saying (indeed, I already said it): Darwin did not know how inheritance works, but his theory does not depend upon that, it just depends on the fairly obvious fact that offspring do, somehow, inherit characteristics from their parents.
And yeah, it is all a lot more complicated than Mendel thought, too, but, as you say, none of these complications of the theory of inheritance are a threat to the basic Darwinian insight.
I think that’s covered by “Inteliigent design” in the OP. Aliens may not be what most ID proponents actually have in mind, but advanced non-mystical alien beings uplifting earthly organisms is ID… 'course that doesn’t help all that much, just pushing the problem back a generation unless one is only interested in how life “on Earth” originated.
Exogenesis via panspermia is a variant of this with unintelligent aliens I guess.
Wasn’t this after the extinction of the dodos? Surely Lamark would have realized that species (and their entire line) could go extinct. Maybe he just thought it didn’t happen very often?
Directed Panspermia is a term used to refer to the idea that life is spread by technologically advanced aliens. While technically you could use intelligent design to mean “life was created by aliens”, I’ve never heard of it being used that way. It always is used by and in reference to the religious crypto-creationists.
Yes, good point. I am not sure what (if anything) Lamark had to say about the Dodo. He might, I think, (consistent with his principles) have dismissed it as an irrelevant, non-natural case of extinction, since humans were responsible, but I am not sure whether he ever actually said anything like that.
But, in any case, I should admit that I was oversimplifying by implying that it was axiomatic for Lamark that extinction does not occur. The point is, more that Lamark’s theory is designed to explain away apparent extinction as illusory, whereas, for Darwinian theory, it is very real and essential to his explanation of the origin of species (if there was no extinction there would be no distinct species, because all the intermediate forms would still be around).
Already, in the 18th century, and quite apart from any sort of Biblical literalism (which had little if any sway back then), paleontology was raising serious problems for Christianity. Fossil discoveries seemed to show that there had once been species on Earth that had now gone extinct. This appeared to be inconsistent with the doctrine (much more crucial to Christianity than a literal reading of Genesis) that God is omnipotent, omniscient and benevolent (or even just that He is just very powerful, very smart, and basically good). If God created species that He then allowed or caused to go extinct, this suggests that He is either incompetent or wantonly cruel. Lamark’s theory is designed to address this problem: fossil forms that we no longer find in living organisms have not really gone extinct, they have simply evolved into different forms that are still around today.
Actually, Lamark’s theory is not even intended to explain the diversity of species, in the way that Darwin’s does. Darwin presents a picture in which one ancestral form differentiates, over geological time, into many diverse species. Lamark, however, retains the basic creationist idea (although not in its Biblical form) that each species around today has come into being separately. (I think he leaves it open whether this is by God’s fiat, or spontaneous generation from muck, or whatever.) In any case, as he sees it, each species (or lineage) originates as a fairly primitive organism, and gradually, over time, evolves into something much more complex and “advanced”. Simple, “primitive” organisms that are around today are, for Lamark, evidence that some species/lineages came into being relatively recently, and so have not yet got very far along with their process of evolution.
My underlying point, which I hope is now clear, was there was a lot more to the difference between Lamark and Darwin than the difference between natural selection and inheritance of acquired characteristics as mechanisms for evolution. Really, the two theories were designed to solve quite different sets of problems. This was the point I was trying to make when I said that Lamark held that species never go extinct, but in trying to be brief, I oversimplified.
Incidentally, it has never been clear to me what problem theories of panspermia (intelligently directed or otherwise) are meant to solve. Panspermia might explain life on Earth, but it leaves you with the problem of how the organisms that seeded the Earth originated. So far as I can see, the alternatives are the same as those we have if life originated on Earth: either the aliens arose from abiogenesis followed by evolution, or they were created/designed by a supernatural power (or by other aliens, whose own origins will then need explaining in their turn).
One (creationist) book I read claimed it was the problem of the prehistoric atmosphere not being conducive to the creation of life due to too much free oxygen. It claimed oxidation in the fossil record indicated an oxygenated atmosphere, and that all experiments required the removal of oxygen to work.
You would have to question why would that have been done.
So that 144 hours 6000 years later when some humans came up with methods of determining the Earth was much older than 144 hours 6000 years that other humans could not believe them.
I am stuggling with the motivation for such a weird act.
Well, for one thing it used to be thought that life was much less likely to appear than it is these days. Panspermia basically tried to solve that by saying “Well, even if it’s really unlikely to have appeared on Earth by itself, the odds of life appearing somewhere in the larger universe are much higher, and once it appeared, it could spread.”
It’s aliens all the way down.
But that is just false according to everything I have ever heard. There was no significant free oxygen in the prebiotic atmosphere. Indeed, as oxygen is highly reactive with many of the other elements found in abundance on Earth, such as hydrogen and carbon, there would not be any any free oxygen in the atmosphere even today if it were not that plants continuously produce it.
Of course, I don’t expect religious creationists to care much about facts or logic. They often just make shit up. But I thought the panspermists held themselves to slightly higher standards. (And I do not really understand why creationists should be interested in lending credence to panspermia.)
I suppose that must be the reason, but why should anyone have thought that they had a good enough handle on the probabilities to make this a plausible argument? Indeed, why should anyone think that now? There are far too many imponderables about abiogenesis (and, come to that, about conditions on the early Earth, and elsewhere in the universe) for anyone to be able to give any decent estimate of its likelihood. It seems to me that all we can say is that it is probably a pretty chancy matter, but we know it happened at least once.
We only KNOW there is life here. Different ideas about how it started make more sense to some than others. This being GQ, I will continue to leave out my personal opinions.
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This is GQ, not Great Debates. Religious (and anti-religious) jabs do not belong here. Do not do this again.
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This is what I understand isn’t correct. Epigenetics does not depend on differences in reproductive success, while Darwin’s evolution does.
The point of Darwin’s evolution is not that traits get passed along through reproduction, it is that they become more or less common depending on whether they are associated with more or less reproductive success. Epigenetics does not depend on this.
If by “evolution” we mean changing genomes, then epigenetics would not be a form of evolution, but if we mean how species change their characteristics, then it would. It’s something that subgroups of a species are doing. I think it is interesting in that it is similar to Darwinian evolution but separate from it, parallel with it. And it is not in the individual, it is in subgroups of a species.
The classic explanation of Darwinian evolution often includes remarking that if you keep cutting the tails off of generations of mice, the next generation still has tails. Epigenetics comes a bit closer to changing this.
Not sure I’m getting this. Mostly, epigenics are inherited factors, just not through DNA. I don’t recall Darwin stating reproductive success as the only factor, as much as survivability of variations that were better suited to an environment would gradually change the common features of a species. Epigenics does present in some cases a manner of change that is not inherited. But then it operates as a mutation does, a non-inherited change. I don’t think Darwin understood mutation, and considered variation to be limitless within his understanding of inheritance.