Hola! I've reordered Nick's reply slightly, 'cause I want to deal with this bit first -
On 28/12/2007, at 1:23 PM, Nick Arnett wrote: > > > I hope nobody here has imagined that I disagree for a moment with the > historical reality of evolution. Nope! I was just laying it out again, 'cause Henry bloody Morris bloody III gives me the shits and I have to have a rant to get it out of my system. :-) > My only doubts, which aren't really even > doubts, but a belief that there are significant discoveries yet to > be made, > are about the mechanisms at work. Yep. I've been meaning to write a slightly more detailed post about possibilities in that area, and I'll try to get to that again sometime soon. I think the main point is that we know a lot about the most common mechanisms of evolution, but there are plenty of less common ones that play their parts. And while evolution itself is pretty well understood, the dynamics of communities that act as boundary conditions to selection pressures, or even as catalysts to selection pressures, are less well understood. As I've alluded to before. Right, that dealt with, back to the meat. > : > >> >> >> 4) Over enough generations, different selection pressures applied to >> different parts of a population (or even just drift, if the >> geographic >> range is significantly larger than the geographic range of family >> groups), causes enough accumulated change to prevent those >> populations >> from breeding if they cross paths, at which time they are said to >> have >> speciated. > > > Except... that a species often isn't clearly delineated. IIRC, > there are > many species, oops, kinds of seagulls that can interbreed with those > who > live nearby, but they can't interbreed with the ones that are > further away. That's actually not an exception to what I wrote. What you're describing is a "ring species" (you're thinking of Black- backed and Herring Gulls around the Arctic Circle probably), and that's an example demonstrating exactly what I said - at the extremes of range, if you introduce members of those populations to each other, they cannot (or will not) interbreed. That you can trace a chain of interbreeding populations across the extent of the range, from one to the other is simultaneously proof of concept (you're demonstrating that these two populations are related), and irrelevant (that there are intermediates traceable between the two ranges does not make these two populations any less distinct). Species concepts are fuzzy, because life is fuzzy. Different species concepts are applied to eukaryotes and prokaryotes, and to sexual vs asexual organisms. Plants can be different again. None of that takes anything away from my paragraph above, which is the basis of speciation (which is really just a barrier to reproduction). > > > And there are animals that are pretty much unable to breed for > physical > reasons -- dogs whose physiologies are so different that it just > doesn't > work. Yes, and if some disaster were to befall every dog breed except Great Danes and Chihuahuas, that would be a speciation event. :-) Your point is valid, and shows how tricky defining species can be - there are whole groups of beetles of which the member species can only be told apart by the shapes of the male and female genitalia, which fit together like lock and key. So why are separate dog breeds not regarded as species? The main reason is because it would not be useful to do so - we know most breeds happily make mongrels, and we know that on the whole, crossbreeds are healthier than pure breeds (hybrid vigour vs inbreeding). So we know that all these dog varieties are maintained by the artificial breeding and eugenics programs of the Kennel Club, and if that were taken away, dog variability would naturally decrease in some ways. > > > I don't mean this just to be picky. I'm not sure what significance > to give > the second point, but the first one is pretty hard to deal with from a > creationist standpoint. I don't recall anything that says God > created a > continuum of similar creatures. No, it's pretty non-specific. It does say that rabbits chew the cud in both Leviticus and Deuteronomy, mind. So possibly not the best source for accurate biology. > But creationists consistently > under-estimate God's abilities. As well as refusing to define what a "kind" actually is. And, indeed, knowing anything about actual science. Or telling the truth. "Lying for Jesus" should be their motto. > > >> >> incorporated into the neo-Darwinian synthesis of Mayr, >> > > Ernst Mayr! I've been trying to remember his name. When I was in > high > school, learning genetics (on my own -- it fascinated me), Mayr > spoke at the > college where my dad taught. I got to meet him. I remember that he > had the > audience try to roll their tongues and explaining that it was an > inherited > ability. Yeah, it's a classic example, and one that's in most school biology textbooks 'cause it's fun and memorable. He died in 2005 (aged 100!). > > > Here's a quote I just found from him, via Wikipedia: > > "*The idea that a few people have about the gene being the target of > selection is completely impractical; a gene is never visible to > natural > selection, and in the genotype, it is always in the context with other > genes, and the interaction with those other genes make a particular > gene > either more favorable or less favorable. In fact, > Dobzhanksy<http://en.wikipedia.org/wiki/Dobzhansky>, > for instance, worked quite a bit on so-called lethal chromosomes > which are > highly successful in one combination, and lethal in another. Therefore > people like Dawkins in England who still think the gene is the > target of > selection are evidently wrong. In the 30's and 40's, it was widely > accepted > that genes were the target of selection, because that was the only > way they > could be made accessible to mathematics, but now we know that it is > really > the whole genotype of the individual, not the gene. Except for that > slight > revision, the basic Darwinian theory hasn't changed in the last 50 > years*." > > Ahhh... Now I'm thinking Mayr influenced me quite a bit so many > years ago. > Those words do a great job of saying where I think Dawkins and his > ilk go > wrong. Or, indeed, where Dawkins was misunderstood (particularly by Mayr). This here: > , and in the genotype, it is always in the context with other > genes, and the interaction with those other genes make a particular > gene > either more favorable or less favorable." ...is *precisely* Dawkins' point. Dawkins uses the example of the rowing eight in one of his books (I think in _Blind Watchmaker_). Say you have a load of rowers and a couple of boats. You take random sets of rowers and race them. Boats with the better rowers in will do better *on average*, and the coach can then work out his best rowers and put them together. And yes, lethal combinations (a boat of eight excellent left-sided rowers, say...) don't take away from that - those combinations are removed quickly. In the case of a population of real animals, yes each individual is the expression of the complete genotype. But random chance is a factor in an individual's life - the best racehorse can trip, break a leg, and be shot. Whereas across a population, those individuals with better combinations of genes do better on average, and so those genes increase in frequency in the population. Yes, lethal combinations can occur. And they're removed from the game. Dawkins was never talking about selection acting directly on a single gene, and unfortunately Ernst Mayr here "therefore people like Dawkins in England who still think the gene is the target of selection are evidently wrong" is arguing against a straw man version of Dawkins' arguments. Not that Dawkins was right about all, he himself badly misunderstood Gould- Eldredge's punctuated equilibria, and that lead to a bitter argument in the letters pages that took a couple of decades to resolve, and his own definition of a gene as used in _Selfish Gene_ is circular, and not the same as what a geneticist would use. Thing is, both viewpoints are perfectly correct - selection works both on the individual and on genes. It's the same kind of thing as the wave/particle duality of light - how you treat it depends on what aspect you're looking at. In the case of evolution, sometimes it makes sense to look at individuals, sometimes it makes sense to look at gene frequencies, sometimes as groups or populations, and until you're capable of seeing things all ways, you're missing a major dimension of what's going on. Mayr was fabulous too, btw, and greatly missed now, as he was the last of the great neo-Darwinians of the Modern Synthesis from that heady time in the 30s and 40s. He just didn't like the trendy new biology of the 70s and 80s (which wasn't really trendy or new, it was just some new perspective which the advent of computers has allowed). Dobzhansky is still well worth reading too, particularly his classic essay "Nothing in Biology Makes Sense Except in the Light of Evolution" here: http://www.2think.org/dobzhansky.shtml Charlie. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
