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For one thing, evolution can sometimes work by going through several stages, of which the intermediate are not particularly useful but not harmful either. By me

by lambda 13y ago

For one thing, evolution can sometimes work by going through several stages, of which the intermediate are not particularly useful but not harmful either. By mere chance, they happen to last long enough for the actually useful changes to build on top of them. For example, see Lenski's long term evolution experiment with e. coli.[1] He's spent 25 years breeding several populations of e. coli, and freezing samples every 500 generations or so (every 75 days). After about 20 years, he discovered that one of the strains had evolved the ability to metabolize citrate in an aerobic environment, which e. coli normally can't do. Going back to the historical record, unfreezing some of the past samples and repeating the experiment, he found that sample from after generation 20,000 could re-evolve this trait, but clones from before that time could not, indicating that there was a potentiating mutation that that particular strain had had shortly before generation 20,000, which the other samples did not have. Further evidence has shown that it may have actually been two separate potentiation mutations. Beyond that, however, proto feathers would have probably been useful for insulation. They seem fairly similar to down feathers, which are great insulators. Given the the feathers were also colorful, they may also have been decorative, and used for catching the eye of potential mates. 1: https://en.wikipedia.org/wiki/Escherichia_coli_long-term_evolution_experiment https://en.wikipedia.org/wiki/Escherichia_coli_long-term_evo...

andrewflnr 13y ago
But we don't know that those potentiating mutations didn't have some kind of benefit on their own, so that doesn't do much for the question of how proto-feathers provide enough benefit to stick around and spread long enough for the next several million mutations to arrive and turn them into feathers. Is insulation adequate for that?
- lambda 13y ago
  If you take a look at the Lenski paper[1], it says: > The potentiating mutations are not known to confer any phenotype amenable to screening, so there is no simple way to distinguish between potentiated and non-potentiated clones. Now, that isn't conclusive evidence that there was no benefit on its own, but it doesn't sound like there's any evidence that it did provide some kind of greater fitness. It sounds like all evidence shows that the original mutation didn't provide any particular phenotypic change on its own, it was only after the later mutation that it had any measurable effect. Now, with dinosaurs it's much harder to tell. We obviously can't do any kind of controlled experiments, or observe them directly. But we can offer up a few potential explanations. One is that some mutations can occur without either helping or harming, but later on another mutation can lead to something useful. Or there may be benefits conferred by proto-feathers. Remember, in addition to their similarity to down, proto-feathers are somewhat similar to hair, and may provide many of the benefits that hair provides: warmth, colors which allow either catching the attention of mates or blending in to the background, better sense of touch (you can feel something before your skin brushes against it), better sensation of the wind, and protection from things that may scrape or cut you. According to Wikipedia[2], the insulation and display (colorful feathers for attracting mates) hypotheses seem to be the more probable. Obviously, we're not going to solve this by speculating here on HN, and it may be that the reason can never be conclusively determined because you can't go back in time to run controlled experiments, but based on the evidence we have those theories sound reasonably plausible. [1]: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461117/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461117/ [2]: https://en.wikipedia.org/wiki/Feathered_dinosaur#Primitive_feather_types https://en.wikipedia.org/wiki/Feathered_dinosaur#Primitive_f...

by lambda 13y ago

andrewflnr 13y ago

But we don't know that those potentiating mutations didn't have some kind of benefit on their own, so that doesn't do much for the question of how proto-feathers provide enough benefit to stick around and spread long enough for the next several million mutations to arrive and turn them into feathers. Is insulation adequate for that?

lambda 13y ago
If you take a look at the Lenski paper[1], it says: > The potentiating mutations are not known to confer any phenotype amenable to screening, so there is no simple way to distinguish between potentiated and non-potentiated clones. Now, that isn't conclusive evidence that there was no benefit on its own, but it doesn't sound like there's any evidence that it did provide some kind of greater fitness. It sounds like all evidence shows that the original mutation didn't provide any particular phenotypic change on its own, it was only after the later mutation that it had any measurable effect. Now, with dinosaurs it's much harder to tell. We obviously can't do any kind of controlled experiments, or observe them directly. But we can offer up a few potential explanations. One is that some mutations can occur without either helping or harming, but later on another mutation can lead to something useful. Or there may be benefits conferred by proto-feathers. Remember, in addition to their similarity to down, proto-feathers are somewhat similar to hair, and may provide many of the benefits that hair provides: warmth, colors which allow either catching the attention of mates or blending in to the background, better sense of touch (you can feel something before your skin brushes against it), better sensation of the wind, and protection from things that may scrape or cut you. According to Wikipedia[2], the insulation and display (colorful feathers for attracting mates) hypotheses seem to be the more probable. Obviously, we're not going to solve this by speculating here on HN, and it may be that the reason can never be conclusively determined because you can't go back in time to run controlled experiments, but based on the evidence we have those theories sound reasonably plausible. [1]: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461117/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461117/ [2]: https://en.wikipedia.org/wiki/Feathered_dinosaur#Primitive_feather_types https://en.wikipedia.org/wiki/Feathered_dinosaur#Primitive_f...