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10-17-2002, 03:30 AM | #41 |
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I saw Dawkins and Pinker at a debate a couple of years ago. Dawkins was impressive. He was also impressively grumpy.
At one point a member of the audience accused him of reductionism. You should've seen his face. He looked like he could kill. Very entertaining. |
10-17-2002, 03:12 PM | #42 | |||||
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Okay, I think we are getting somewhere.
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This form of 'evolution' may explain some changes in populations, but it is not going to give you complexity. Environment-instigated population changes can not accumulate, nor progress. Therefore, would you agree that the part it plays in evolution (when separate from genes) is miniscule, temporary, and nearly irrelevant compared to heritable change? Quote:
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I prefer Dawkins' definition: "the non random selection of randomly varying replicators". This definition restricts biological evolution to replicating things, but DOES NOT exclude any other factors acting on that evolution, such as environmental factors. If non heritable change is an evolutionary change, why focus on generations at all? A lifeless earth could be said to have evolving rocks. Whenever it rains, the population evolves toward wetness, and when they dry out, they have evolved toward dryness again. The only reason evolution focuses on multiple generations at all is because when evolution is doing anything interesting at all, it is doing it using heritable traits. [ October 17, 2002: Message edited by: Doubting Didymus ]</p> |
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10-18-2002, 10:23 AM | #43 | |||||
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Doubting Didymus,
Your problem is that you are thinking of adaptation by natural selection as "true evolution" and every other type of change as "semi-evolution." This is simply not true, as I think you realize, but you are still stuck in that trap. Quote:
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10-18-2002, 11:36 AM | #44 |
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I think I understand Rufus's point.
Since the phenotype is always the result of the interaction between the genotype and the local environment, any environmental change that results in a population-wide change in phenotype has effectively changed what certain genes are "for", and should therefore be considered evolution. Does that make sense? |
10-18-2002, 11:59 AM | #45 | |
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There are a couple of issues here. One is what constitutes evolution: many people who are otherwise good 'evolutionists' are uncomfortable with the idea that non- or mal-adaptive change can be considered evolution. These are the same people who often argue that human evolution has "stopped" because we've eliminated some selective pressures. This is, of course, false. Random genetic drift or founder effects are perfectly good examples of evolution in action. Another issue that I alluded to earlier was the involvement of the environment in evolution. This is actually a similar misconception: many people hear the word "environment" and think of rocks and annual rainfall and seasonal variations in temperature and prey availability. These are all parts of the story, but perhaps the largest and most significant component of the environment is the population itself! The two are in many ways indistinguishable. Change the frequency of an allele in a population, and you have effectively changed the environment. |
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10-18-2002, 02:30 PM | #46 | |
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Peez |
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10-18-2002, 03:51 PM | #47 | |
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10-19-2002, 01:18 PM | #48 | |||
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[ October 19, 2002: Message edited by: RufusAtticus ]</p> |
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10-19-2002, 01:37 PM | #49 | |
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Although one virtue of the 'allele frequency' definition is that it is complete and inarguable. |
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10-20-2002, 09:14 AM | #50 | |
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What I had in mind was something like the following hypothetical example: suppose an isolated population of ammonites lives in a body of water in which the concentration of calcium salts is gradually increasing over many ammonite generations. Then suppose that this leads, without any particular genetic change, to later generations of ammonites having thicker shells than earlier ones. Millions of years later, a paleontologist digs up the fossils, notices an unmistakeable trend in increasing shell thickness, and calls it evolution. By the standard definition, the paleontologist would simply be wrong. But there are good reasons not to want to say that. 1. It would make it almost impossible to state with reasonable certainty whether many types of morphological change in the fossil record are evolutionary or not, when satisfying the technical definition really doesn't seem to matter. 2. More significantly, in the ammonite population in my example, genes for 1 mm-thick shells are gradually being replaced over time with genes for, say, 2 mm-thick shells, even though the genes themselves are not changing. This is taking place under the usual conditions of natural selection. If thicker-shelled ammonites don't thrive at least as well as thinner-shelled ones, we would expect the population to either evolve new genes that make the shells thinner again (say be decreasing calcium uptake); migrate down the calcium concentration gradient; or die out. Since I'm stipulating that they haven't done this, it doesn't seem too far-fetched to claim that traditional evolution actually is going on. What do the biologists here think? |
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