Gradualism in Evolution (was Categories ...) (Agnosticism)

by dhw, Monday, July 19, 2010, 08:52 (5023 days ago) @ George Jelliss

In my post of 8 July at 21.24 I asked why Darwin (Natura non facit saltum) considered gradualism to be so essential that his theory would "absolutely break down" if it could be demonstrated "that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications." My point is threefold: (1) That even a single cell is staggeringly complex, so where does the scale of complexity begin? (2) That all mutations, innovations, adaptations to new conditions represent jumps in Nature, and if they didn't work ... even in their most rudimentary form ... they wouldn't survive. (3) That the theory of punctuated equilibrium fits in far better with the fossil record as we know it.-George has kindly offered me a possible explanation, quoting Ernst Mayr: -"Individuals in a single population may differ by visibly different characters" (he cites eye colour and number of molars). I don't think this has any bearing on the way complex organs arise out of mutations or adaptations.-"A successful mutation with a large phenotypic effect can be gradually incorporated into a population as long as it is able to pass through a period of polymorphism in which it coexists with the previous phenotype until it has completely displaced the original gene." 
That makes sense to me, but misses the point at issue, which is that a successful mutation will already entail complexity ... it will involve an innovation which works, i.e. a jump, not a gradual development. A light-sensitive nerve is a jump from a nerve which is not light-sensitive (and where did nerves come from in the first place?). In passing, one might also question why a phenotypic mutation should take place if the original gene is already well suited to its environment. -"It must be remembered that there is a considerable range in the size of the mutations that lead to evolutionary change."
Well, OK, maybe a small mutation is only a small jump, but a big mutation will be a big jump.-"Darwinian gradualism is due to the gradual restructuring of populations."
No it isn't. The gradualism so vital to Darwin is the formation of complex organs through mutation and adaptation. It seems reasonable to me to argue that new organs will gradually be refined and improved by natural selection. However, it does not seem reasonable to me to assert that mutations and adaptations are initially NOT complex, and that such innovations can only come about gradually. If an innovation is not successful, it will not survive. This does not in any way undermine the theory of evolution, and so I remain as mystified as ever by Darwin's insistence. All the same, I'm grateful to George for making the effort to enlighten me. Any other suggestions? -Coincidentally, there was an article in yesterday's Sunday Times, under the heading 'Conan' bug may be source of life. The bug, called Deinococcus radiodurans, is so tough that it could survive space travel. Professor Ivan Paulino-Lima, a biophysicist in Rio de Janeiro, has published a paper in Planetary and Space Science, describing the various tests on this bug, which was first discovered 50 years ago after a can of corned beef went rotten despite having been sterilized by radiation. "The discovery has excited astronomers, who have long speculated that the debris ejected into space when planets are struck by large meteorites might be able to transport such microbes between planets, thus spreading life." Scientists are therefore suggesting that "such organisms could have been the origin of life on Earth." Maybe, though that should not be confused with "the origin of life". -The sting is in the tail: "The most likely explanation for the germ's toughness is that each bug possesses four to 10 copies of its genome, rather than the usual single version. It also has a highly efficient repair system, so even if the DNA is ripped apart by radiation, bits can easily be spliced together again." Can you imagine a greater jump than that from inanimate matter to a bug that can reproduce itself, survive in any environment, and repair itself? And why would such an organism need to evolve into other organisms when it is already so perfectly equipped for survival? And why would its genome evolve into the far less efficient "usual single version"?