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Two notes. The first is for fun. See the miniature lasso that he used? It is easy to tie one out of a long blade of grass and catch lizards that way. The trick

by btilly 3y ago

Two notes. The first is for fun. See the miniature lasso that he used? It is easy to tie one out of a long blade of grass and catch lizards that way. The trick is that they've been adapted to ignore grass as a non-threat. So when they're about to be captured by a piece of grass, they literally can't see the grass. You have to remain far enough away, but you can bonk the lizard on the nose, pull your grass back, readjust and try, try again until you get it. It's a great trick to show kids! The second is that no mechanism is needed to revert a temporarily selected trait. Francis Galton was the first to document regression to the mean in inheritance. The child of two tall parents tends to be not as tall. The child of two short parents tend to be not as short. The reason this happens is that the recessives that influence the one parent's trait are often different from the recessives for the other parent. Therefore the child winds up expressing fewer recessives than either parent. What this means is that if you select for a given complex trait in a given generation, those who survive will have that trait. But unless you also select for it in the next generation, the population will mostly revert back on its own. It is only regular selection, sustained over time, which causes the selected for trait to breed true.

pests 3y ago
This plays slightly into the slow climate change vs fast climate change issue. If climate changes slowly enough, this allows enough generations to build up the new traits needed for survival. Too fast, nothing lasts to evolve at all.
- Terr_ 3y ago
  That makes me think of how--IIRC--amphibian genomes contain coding for a lot of different proteins that have about the same function but are stable/effective at different temperatures, especially during early development in the egg. (In contrast, mammals invest in genes that ensure the egg's external temperature is reliable.) (See also: Orthologous proteins, Heat shock proteins.)
williamdclt 3y ago
> It's a great trick to show kids! Kids are cruel :( showing them how to hunt lizards is likely to lead to their torture and/or death
- throwup238 3y ago
  The trick is to make them eat anything they kill. "You kill it, you eat it!" That'll work the cruelty right out of them and set them up for a promising life post nuclear apocalypse. Lizards will bioaccumulate less fallout from the food chain than larger animals so they'll be a safer source of protein.
  - mathgradthrow 3y ago
    why would smaller animals accumulate less fallout?
    - wizardwes 3y ago
      It's more location in the good chain than size, and volume of food eaten vs body volume
- PH95VuimJjqBqy 3y ago
  Me and my brothers hunted horned toads for years without ever killing any of them. I don't exactly think we were special either.
- girvo 3y ago
  Depends how the kids are raised I guess. My brothers and I never tortured and killed any of the skinks we’d catch as kids
- breather 3y ago
  Damn what kind of kids did you hang out around
gwern 3y ago
> The reason this happens is that the recessives that influence the one parent's trait are often different from the recessives for the other parent. Therefore the child winds up expressing fewer recessives than either parent. That's wrong. Regression to the mean has nothing to do with recessives (or dominance, or epistasis), and exists with purely additive effects (and everywhere in statistics, for that matter, anywhere that a correlation is not perfect). It is simply because the phenotype has r < 1 with the genotype (ie. the trait is not 100% genetically determined), so when you select the 'high' organisms, they are lucky on both genotype and 'environmental' variables. The environmental variable goes away, however, and only the higher genotype variable persists. Since that was only a part of why the parents were 'high', the highness is not as high. > What this means is that if you select for a given complex trait in a given generation, those who survive will have that trait. But unless you also select for it in the next generation, the population will mostly revert back on its own. It is only regular selection, sustained over time, which causes the selected for trait to breed true. This is also wrong. The effect of the selection is permanent and has already 'bred true' and will persist indefinitely unless undone by some other force. It's a ratchet, not a rubber band.
- wolverine876 3y ago
  From the Stroud et al 2023 paper reviewed in the article: Species’ phenotypic characteristics often remain unchanged over long stretches of geological time. Stabilizing selection—in which fitness is highest for intermediate phenotypes and lowest for the extremes—has been widely invoked as responsible for this pattern. But, say Stroud et al: However, even with an explosion of microevolutionary field studies over the past four decades, evidence for persistent stabilizing selection driving long-term stasis is lacking. Stround & co's answer: Here, by directly measuring natural selection in the wild, we identified a complex community-wide fitness surface in which four Anolis lizard species each occupy a distinct fitness peak close to their mean phenotype. 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.
  - gwern 3y ago
dekhn 3y ago
height is controlled by thousands of genes each of which provides a small effect, and the relationships between those genes are non-trivial. i don't think concepts from mendelian inheritence (like recessive) are super-meaningful in cases like this.
- eru 3y ago
  Btw, doesn't Mendelian inheritance only really work for species with two copies of each chromosome? Lots of plants have many more copies. I guess Mendel got lucky that he investigated plants that were simple enough. (And from what I've read, his research assistants actually cheated him: the numbers he got were too close to the theoretical averages, the variances were much smaller than math would predict. His assistants made the numbers come out like the boss expected them.)

by btilly 3y ago

pests 3y ago

This plays slightly into the slow climate change vs fast climate change issue. If climate changes slowly enough, this allows enough generations to build up the new traits needed for survival. Too fast, nothing lasts to evolve at all.

Terr_ 3y ago
That makes me think of how--IIRC--amphibian genomes contain coding for a lot of different proteins that have about the same function but are stable/effective at different temperatures, especially during early development in the egg. (In contrast, mammals invest in genes that ensure the egg's external temperature is reliable.) (See also: Orthologous proteins, Heat shock proteins.)

williamdclt 3y ago

> It's a great trick to show kids! Kids are cruel :( showing them how to hunt lizards is likely to lead to their torture and/or death

throwup238 3y ago
The trick is to make them eat anything they kill. "You kill it, you eat it!" That'll work the cruelty right out of them and set them up for a promising life post nuclear apocalypse. Lizards will bioaccumulate less fallout from the food chain than larger animals so they'll be a safer source of protein.
- mathgradthrow 3y ago
  why would smaller animals accumulate less fallout?
  - wizardwes 3y ago
    It's more location in the good chain than size, and volume of food eaten vs body volume
PH95VuimJjqBqy 3y ago
Me and my brothers hunted horned toads for years without ever killing any of them. I don't exactly think we were special either.
girvo 3y ago
Depends how the kids are raised I guess. My brothers and I never tortured and killed any of the skinks we’d catch as kids
breather 3y ago
Damn what kind of kids did you hang out around

gwern 3y ago

> The reason this happens is that the recessives that influence the one parent's trait are often different from the recessives for the other parent. Therefore the child winds up expressing fewer recessives than either parent. That's wrong. Regression to the mean has nothing to do with recessives (or dominance, or epistasis), and exists with purely additive effects (and everywhere in statistics, for that matter, anywhere that a correlation is not perfect). It is simply because the phenotype has r < 1 with the genotype (ie. the trait is not 100% genetically determined), so when you select the 'high' organisms, they are lucky on both genotype and 'environmental' variables. The environmental variable goes away, however, and only the higher genotype variable persists. Since that was only a part of why the parents were 'high', the highness is not as high. > What this means is that if you select for a given complex trait in a given generation, those who survive will have that trait. But unless you also select for it in the next generation, the population will mostly revert back on its own. It is only regular selection, sustained over time, which causes the selected for trait to breed true. This is also wrong. The effect of the selection is permanent and has already 'bred true' and will persist indefinitely unless undone by some other force. It's a ratchet, not a rubber band.

wolverine876 3y ago
From the Stroud et al 2023 paper reviewed in the article: Species’ phenotypic characteristics often remain unchanged over long stretches of geological time. Stabilizing selection—in which fitness is highest for intermediate phenotypes and lowest for the extremes—has been widely invoked as responsible for this pattern. But, say Stroud et al: However, even with an explosion of microevolutionary field studies over the past four decades, evidence for persistent stabilizing selection driving long-term stasis is lacking. Stround & co's answer: Here, by directly measuring natural selection in the wild, we identified a complex community-wide fitness surface in which four Anolis lizard species each occupy a distinct fitness peak close to their mean phenotype. 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.
- gwern 3y ago

dekhn 3y ago

height is controlled by thousands of genes each of which provides a small effect, and the relationships between those genes are non-trivial. i don't think concepts from mendelian inheritence (like recessive) are super-meaningful in cases like this.

eru 3y ago
Btw, doesn't Mendelian inheritance only really work for species with two copies of each chromosome? Lots of plants have many more copies. I guess Mendel got lucky that he investigated plants that were simple enough. (And from what I've read, his research assistants actually cheated him: the numbers he got were too close to the theoretical averages, the variances were much smaller than math would predict. His assistants made the numbers come out like the boss expected them.)