I think “evolution” should mean changing genomes - that is, traits that are reliably passed over multiple generations. Passing on traits epigenetically is not evolution, but the ability to pass traits epigenetically is evolved and evolvable.
I think of it like tanning. If you migrate south and your skin can darken in response to the increased sunlight, that ability gives you a survival advantage. The tanning ability is a trait your ancestors acquired through evolution and passed on to you. However your darkened skin is not an evolved trait; you will not pass it on to your children. Your children will be born light skinned and must do their own tanning. But suppose your ancestors had evolved the ability not only to tan but to epigenetically pass on their current skin tone. Then your children would be be born with dark skin - but they would not have evolved dark skin. Their genetic makeup in that trait remains the same as yours. If they move north, their skins will lighten, their children will be born lighter, and eventually the darkened skin you acquired will have evaporated. It was not truly heritable. Your ability to pass on your darkened skin was evolved but the epigenetically darkened you passed to your children was not evolution.
Here’s another example: Say a bird eats food containing a foul-tasting chemical, and thus becomes foul-tasting itself. She passes the chemical from her own tissues into her egg, and thus her chick epigenetically acquires the foul taste. Did her line “evolve” a foul taste? I’d say not: the genome has not changed and the foul-taste trait will disappear without continued consumption of the chemical.
I am a bit disappointed in this thread. I try to keep an open mind on this stuff and was hoping for some new ideas. We are doing a fine job of finding intermediate species. I don’t worry about the remaining holes I still struggle with how a new species develops that can no longer interbreed with the old. Yes selective breeding works. An isolated population will have more individuals with traits favored in its environment. But how does the first one to no longer be able to breed ever pass on its genes? I don’t see how to cross the chasm in a series of small steps no matter how long you have.
As for the separate question of the origin of life,.we are still stuck with however unlikely, it did happen at least once.
I assume you are referring to the development of new species. It seems to be a popular, but nonetheless wildly incorrect belief that evolution expects speciation to occur over a single generation from an existing population. Obviously, such an occurrence would be exceedingly unlikely for a sexually reproducing organism for the reason you state.
However, that is not how species form. Populations evolve, not individuals. For speciation to occur a population must become reproductively isolated from its main group. Once isolated, mutations that arise in the new population cannot propagate back to the original population and the new population can change independently of the original.
The Wikipedia article on speciation gives a good introduction on the different ways the populations become isolated in the first place.
Exactly. It isn’t a lot different to a form of nurture meme. Epigenics is a species survival mechanism. It improves the ability of the offspring to survive, and to hence procreate. Species that have evolved the ability to pass on useful epigenic traits will do better. Thus it fits perfectly within the standard model of evolution.
It is possible to imagine that it might be possible for something to evolve a mechanism that allows permanent modification of the genome, and that this might eventually evolve into a mechanism that allows Larmarkian evolution in some manner. However the barrier to do so within the usual mutation mechanisms is likely so high that the universe will be cold before such a thing comes about.
In the end it might be possible to simply set the theories into categories of how the information in the genome came about.
[ul]
[li]divine creation/ intelligent design - the information is created fully formed and does not change. [/li][li]divine guidance - the information is mutated under the control of a divine/intelligent outside force.[/li][li]Lamarkian - the information contains mechanisms for self directed modification that will advantage the species.[/li][li]Darwin - the information is mutable, but mutates in an unguided manner, natural selection winnows out most mutations. [/li][/ul]
It isn’t clear what other category there might be. One has the spread from fully controlled information in the genome to randomly varying information. You can’t get any less controlled than random change, nor any more controlled than divine creation. In between is where you might find traction for another theory. But evidence is likely pretty thin.
Some small scale wiggle room might exist. I heard the idea years ago (with no recollection of where sadly) that stress might be used as a mutation trigger, and species that include this mechanism will begin to produce more variation in times of high stress on the species, with the result that there is a greater chance that some sub-population might survive. This could be considered a hybrid Larmarkian Darwinian mechanism. External factors cause the mutation, but it is undirected and natural selection picks of the winner. Like epigenics, one would probably regard this as simply another evolved species survival trait, and again consistent with Darwin.