| thanny said: Im actually interested to hear an evolution based explanation of the point Dioxinis initially made. It seems to be a good point to me; I can understand how if an organism had, for example, eyes, it would give it a survival advantage... natural selection etc. But that would never mutate all at once, one single part of it would have to mutate, and that single part would have to give it a survival advantage. I dont really see this happening. This logic can be applied to any body part, really. Just about all of them need all of their parts to work. ... |
That thesis (irreducible complexity of bacteria flagella) was the famous claim of Dr Micheal Behe, supporter of ID, and has been rejected by the scientific community at large.
Several studies have shown that there are precursors of the proteins partecipating in the rotor attending different roles in other bacteria. Moreover, phylogenetic analysis of genes in very well known genomes of bacteria have traced all the genes intervening in the flagella rotor mechanism and their variants in different phyla and thus it was possible to infer the sequence in which the mechanism originated through gene combination and variation.
As for the eye, it's again one example of a structure that is very complex in its end stage, but you can get there through progressive steps each of which has advantages relative to the previous one, thus retaining a selective pressure (it's actually the exact example Dawkins tackles in The Blind Watchmaker). You can start by an animal having a photosensitive area of skin: that's not as good as an eye, but it gives an advantage in sensing the shadow of a predator before touch comes into play. If the sensitive area recesses into an open cavity, it gains progressively more directional focus. Muscles to orientate the cavity give an obvious further advantage. Close the cavity with a transulcent tissue and fill it with a transparent fluid and you can have bigger and more sensitive areas. If the translucent lid grows curved like a lens it can offer variable focus...
Really, the complexity of the final structure can be decomposed in a number of simpler steps. Please note that if intelligent design was behind our eyes, it would not be that intelligent, as our retina has photosensitive cells pointing "the wrong way", with the sensitive part poitning inwards, and the "cabling" part pointing towards the light and converging to cause our blind spot. The same is not true e.g. in octopi, where the retina cells are oriented correctly, but scientists believe have evolved an eye indipendently from vertebrates. Also note that the Nautilus has "lensless" eyes, open to the water environment, that work a bit like the pinhole boxes you can make to observe an eclipse. That sounds like further proof of the utility of "intermediate" eye models.
Plus, from a methodological point of view it can be hard to understand how a complex structure was originated by steps. That doesn't excuse us from trying to find the steps without resorting to outlandish metaphysical explanations, and up to this point the scientific community has never found a real case of irreducible complexity.
I suggest you google for Behe, irreducible complexity, "Krebs cycle shunt" if you want to get technical.
