From: Rowan Crawford 9/02/99 19:14:09 Subject: Evolution: 3rd rule post id: 664 When talking about evolution, books always mention two things that drive it; random differences in the copying process, and natural section. Is it possible that a 3rd rule might be part of it; -forced- changes? Is it possible to actually change your DNA by continually doing something (either by choice or naturally forced somehow) so that the reproduction (new cells with DNA or even offspring) will have the change built in from the start? As an example, lets say I decided that from now on until the day I die I was going to get around by hopping only on my right leg. If my offspring was then to do the same for their entire life, and then their offspring as well (etc), would the DNA change over the generations to take this into account and create a stronger right leg (perhaps centered under the body instead of to the side), and weaken the other one so it wasn't in the way? I realize that just by doing that for any length of time you'd see physical changes, but I'm curious to know whether something like that can be 'forced' into the DNA sequence? Evolution really spins me out; I find it hard top comprehend how just random errors and natural selection could end up at something like a human (or even a fish for that matter). Cheers, Row. From: Sue 9/02/99 20:20:56 Subject: re: Evolution: 3rd rule post id: 665 Lamarck had that idea, but unless someone has tried to resurrect it, that's been discredited. Mathematics is more useful. Reproductive excess and survival of the fittest drive evolution. The mutations involved are random mutations. Evolutionary change is usually slow, so we don't see a lot of it in our lifetimes. Interestingly enough, the rate of evolution can increase in areas with a higher than normal background radiation. As most mutations are harmful, that's not good news for individuals. Just for a species. If the whole species doesn't succumb to radiation-related disorders fist, that is. (Then we're back to cockroaches, if we are to believe that story.) From: James Richmond (Avatar) 9/02/99 21:46:52 Subject: re: Evolution: 3rd rule post id: 676 Lamarck's theory can be summarised by the phrase "inheritance of acquired characteristics". He thought, for example, that giraffes got their long necks by straining to get leaves at the tops of trees. If a giraffe spent its life straining its neck upwards, its offspring would have slightly longer necks. Classical Darwinian evolution allows no room for this type of inheritance. Changes in the genes of a species occur solely due to the occasional random mutation. Some changes are good; most are neutral or detrimental. Good ones tend to propagate if they make it more likely for the organism containing the good genes to reproduce. But this may not be the whole story. Cells contain genes, but they also inherit an "instruction manual" which tells the genes when to become active, and to what extent. This instruction manual is called epigenetic information. There is some evidence which has come to light recently that changes to the epigenetic instructions can be passed from generation to generation, contrary to the previous theory that the epigenetic "slate" is wiped clean during the formation of sperm and egg cells. Some biologists have suggested that this may provide a mechanism for populations of organisms to quickly adapt to short term changes in their environments, which normal genetic evolution is too slow to cope with. More information on epigenetic inheritance can be found in an article published in New Scientist last year, at http://www.newscientist.com/ns/981128/epig.html. One example given there is of the pregnant Dutch women who starved during the famine of the Second World War. Not only did they have smaller than average babies, but those babies went on to have small babies of their own, even though the postwar generation was well fed and no genes had been altered. From: jim bashford 10/02/99 11:09:51 Subject: re: Evolution: 3rd rule post id: 713 Sometime last year I read about a form of inheritance not relying on genetic material, in New Scientist. The idea being that some protein fragments (prions) can freely pass between cells and are responsible for regulating the shapes of existing cellular proteins. They'd found a beneficial example of this (c.f detrimental, like "mad cow" disease) in yeasts I think. It's weird - it's not genetic inheritance, but the principle is slightly closer to Darwinism than Lamarckism I guess. Does anyone know anything more? cheers Jim From: Kate 10/02/99 19:51:29 Subject: re: Evolution: 3rd rule post id: 773 "As an example, lets say I decided that from now on until the day I die I was going to get around by hopping only on my right leg. If my offspring was then to do the same for their entire life, and then their offspring as well (etc), would the DNA change over the generations to take this into account and create a stronger right leg (perhaps centered under the body instead of to the side), and weaken the other one so it wasn't in the way?" The behaviour of hopping around on one leg won't change the DNA passed on to the offspring. But if the ability of hopping on one leg is seen to be a desirable characteristic, then if a child is born who has had a mutation in his/her genes which increases their ability to hop, they will be seen as a better mate (compared to dowdy two-leg walkers), and so the chance of their changed DNA being passed on the subsequent generations is greater. From: Dr. Ed G (Avatar) 10/02/99 20:40:19 Subject: re: Evolution: 3rd rule post id: 775 There was a piece about just this very thing on Robyn Williams's "Ockham's Razor" a couple of months ago called "Lamark's Signature". As I recall the first airing of it was prematurely cut off because of late scheduling. However, if you want to read the full transcript you can find it at Lamarck's Signature It seems that yes indeed there might be some Lamarkian processes going on after all. Soupie twist, Ed G. From: Rowan Crawford 11/02/99 0:53:52 Subject: re: Evolution: 3rd rule post id: 788 There's actually another aspect of forced DNA changing that I wonder about and that is in cases where the body seems to accept a large change as permanent. Another example; lets say I amputated my leg (I've stopped hopping now, so it doesn't matter which one) - over time it would seal off quite neatly rather than grow back. The puzzle is that DNA in every cell contains the shape of my whole body and those cells are contunually being created so why doesn't the leg grow back to how it was? Instead it seems that it's said to itself "that looks like a big task, lets try something easier" and so it changes the DNA instructions to instead just neatly round off the leg. There are examples of it happening the other way; I accidentally cut a chunk out of my thumb once and it (eventually) grew back like nothing had happened. Even the thumb print returned. And yet my cousin cut the end off a finger once and it grew a rounded stump. What system is at work here? Cheers, Rowan. From: Artos 14/02/99 13:32:04 Subject: re: Evolution: 3rd rule post id: 1152 There seems to be one thing bothering me about the discussion on evolution, especially as it pertains to natural selection... There has been mention made of "beneficial", "neutral", and "non-beneficial" random changes in DNA. Surely, these are subjective tags to attach to these random mutations? Such changes (as I understand it) aren't intrinsically "beneficial" or "harmful" - except where they result in a disease or deformity that mitigates against survival. My understanding is that these random changes are exactly that - random. What makes them "beneficial" or "harmful" is whether or not the changes result in an organism that, entirely coincidently, is better suited to the environment in which it finds itself than the "parent" organism. I believe this is what Wallace meant by the term "survival of the fittest" which is so misused and misunderstood. By "fittest", he did not mean "strongest", or "most ruthless" or necessarily even "most intelligent" - merely that organism which was the "most fit" for the environment in which it existed. I would appreciate feedback on this. Artos From: Robbie Gates 14/02/99 17:58:37 Subject: re: Evolution: 3rd rule post id: 1161 The words beneficial and harmful are to aid us in talking about evolution - much the same as we might say a gene wants to make copies of itself. To be completely precise, wherever you read beneficial mutation in a discussion of evolution, you should pretend you read mutation which increases the average number of offspring surviving to reproductive age. This is a bit of a mouthful, hence the common usage of beneficial. One important thing to note is that its not even what the mutation does for you that matters - its the effect it has on you producing viable offspring. Usually these are closely related, but one occasionally needs to be careful. Note also here that i've restricted attention to genes that propagate by reproduction (e.g. i've excluded viruses). Your (Artos) analysis of fittest is pretty much on the mark. You don't even need to be superlative about it - all my genes need to do to end up having a larger share of the gene pool is to produce, on average, more viable copies of themselves in my offspring than competing genes. However, humans tend to lapse into informal reasoning, hence the use of terms like strongest, most ruthless, &c The other thing to keep in mind is that strongest is often correlated with more succesful reproductively (e.g. elephant seals), but this is not the only strategy that works. We often talk coarsely, using terms like strongest, but one should always think through the arguments in pure fitter than thou context to be (more) confident of them.