4 ms·

Indeed. As I said, "The effect of the selection is permanent and has already 'bred true' and will persist indefinitely unless undone by some other force."

by gwern 3y ago

wolverine876 3y ago
I gotta say, I don't quite grok your statement. Evolutionary biologists say selection effects are high in the very short-term, but very low in the long term - many creatures are basically the same for millions of years. That's the 'paradox of stability'. I don't understand how your statement explains the long-term stability part. From the Quanta article: With enough time, even the tiniest tugs should yield a measurable shift in an organism’s observable characteristics. If the beak-size changes the Grants observed [over a few years] continued over millennia, back-of-the-envelope calculations predicted some extreme phenomena, Pennell said. “You’d expect finches that were, like, 40 kilograms. This just makes no sense.” How does your theory not produce 40 kg finches? And in fairness, I sure don't have a theory other than what I read, so it's asked in the spirit of curioisty.
- gwern 3y ago
  I don't understand your confusion. I thought the Quanta article did a perfectly reasonable job of explaining the difference between stabilizing selection for a single fixed, permanent, unaltered optimal phenotype, and having simply a bit of selection randomly different each year which nets out to no change. Lots of random changes average out to nothing, but each change was still a change. If you ratchet something a little bit one time, then ratchet it the other way randomly a bit, etc, it is still ratcheting each time, but it's not going to produce 40 consecutive clockwise spins.
  - wolverine876 3y ago
    I guess my interpretation is that the biologists say it does not average out and we would end up with 40 kg finches, and that another mechanism is needed to explain it. They used to think that mechanism was stabilizing selection, "fitness is highest for intermediate phenotypes and lowest for the extremes", but the evidence doesn't support it. As far as I can tell, the article omits the mechanism. Stroud's paper describes it thusly, though to me it doesn't seem so different from stabilizing selection, other than maybe the variations aren't smoothed out as immediately (from the abstract; in the body Stroud describes other theories as valid, but I haven't had time to sort it out): The presence of local fitness optima within species, and fitness valleys between species, presents a barrier to adaptive evolutionary change and acts to maintain species differences through time. However, instead of continuously operating stabilizing selection, we found that species were maintained on these peaks by the combination of many independent periods among which selection fluctuated in form, strength, direction, or existence and in which stabilizing selection rarely occurred. I'm getting the impression that the significance of Stroud's paper might be less the mechanism, and more that stability occurs on 'milli-scales' (my term), the short period of Stroud's data, in contrast to high variability on micro-scales (as shown in the Grants' finch research) and the well-known stability on mega-scales (millions of years). The article returns many times to the value of Stroud's long-term, high-quality data collection. Because he had followed four species for three generations, he was able to show that a long-term pattern of stasis could emerge from such short-term fluctuating selection. But I don't see how that differs from the Grants's finch data, which was over more time and was at least two generations, and I think more. Also they say: Fully resolving the paradox will require scientists to study time spans between macro- and microevolution, Porto said — on the scale of tens, hundreds or thousands of years. They need to find a sweet spot that is long enough to allow both change and stasis to emerge, he said, although at the moment biologists don’t have a long enough data set to draw from. Anyway, I am happy to keep talking, but I need to read something else today - something that I get paid to read! :)

Indeed. As I said, "The effect of the selection is permanent and has already 'bred true' and will persist indefinitely unless undone by some other force."

by gwern 3y ago

Indeed. As I said, "The effect of the selection is permanent and has already 'bred true' and will persist indefinitely unless undone by some other force."

wolverine876 3y ago

I gotta say, I don't quite grok your statement. Evolutionary biologists say selection effects are high in the very short-term, but very low in the long term - many creatures are basically the same for millions of years. That's the 'paradox of stability'. I don't understand how your statement explains the long-term stability part. From the Quanta article: With enough time, even the tiniest tugs should yield a measurable shift in an organism’s observable characteristics. If the beak-size changes the Grants observed [over a few years] continued over millennia, back-of-the-envelope calculations predicted some extreme phenomena, Pennell said. “You’d expect finches that were, like, 40 kilograms. This just makes no sense.” How does your theory not produce 40 kg finches? And in fairness, I sure don't have a theory other than what I read, so it's asked in the spirit of curioisty.

gwern 3y ago
I don't understand your confusion. I thought the Quanta article did a perfectly reasonable job of explaining the difference between stabilizing selection for a single fixed, permanent, unaltered optimal phenotype, and having simply a bit of selection randomly different each year which nets out to no change. Lots of random changes average out to nothing, but each change was still a change. If you ratchet something a little bit one time, then ratchet it the other way randomly a bit, etc, it is still ratcheting each time, but it's not going to produce 40 consecutive clockwise spins.
- wolverine876 3y ago
  I guess my interpretation is that the biologists say it does not average out and we would end up with 40 kg finches, and that another mechanism is needed to explain it. They used to think that mechanism was stabilizing selection, "fitness is highest for intermediate phenotypes and lowest for the extremes", but the evidence doesn't support it. As far as I can tell, the article omits the mechanism. Stroud's paper describes it thusly, though to me it doesn't seem so different from stabilizing selection, other than maybe the variations aren't smoothed out as immediately (from the abstract; in the body Stroud describes other theories as valid, but I haven't had time to sort it out): The presence of local fitness optima within species, and fitness valleys between species, presents a barrier to adaptive evolutionary change and acts to maintain species differences through time. However, instead of continuously operating stabilizing selection, we found that species were maintained on these peaks by the combination of many independent periods among which selection fluctuated in form, strength, direction, or existence and in which stabilizing selection rarely occurred. I'm getting the impression that the significance of Stroud's paper might be less the mechanism, and more that stability occurs on 'milli-scales' (my term), the short period of Stroud's data, in contrast to high variability on micro-scales (as shown in the Grants' finch research) and the well-known stability on mega-scales (millions of years). The article returns many times to the value of Stroud's long-term, high-quality data collection. Because he had followed four species for three generations, he was able to show that a long-term pattern of stasis could emerge from such short-term fluctuating selection. But I don't see how that differs from the Grants's finch data, which was over more time and was at least two generations, and I think more. Also they say: Fully resolving the paradox will require scientists to study time spans between macro- and microevolution, Porto said — on the scale of tens, hundreds or thousands of years. They need to find a sweet spot that is long enough to allow both change and stasis to emerge, he said, although at the moment biologists don’t have a long enough data set to draw from. Anyway, I am happy to keep talking, but I need to read something else today - something that I get paid to read! :)