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Thank you for the response. At the risk of digressing from the topic at hand -- steel bones -- I'd reply to your points as follows: You wrote: But that eyebrow

Thank you for the response. At the risk of digressing from the topic at hand -- steel bones -- I'd reply to your points as follows: You wrote: But that eyebrows exist at all is probably tied to some survival/reproductive benefit. I disagree. Not every trait has something to do with conferring a benefit. Many traits are simply random artifacts of an exceedingly complex dynamic system. Your assertion hypothesizes otherwise. That's fine. But, it would be reasonable to expect data to back it up. In my experience, I've seen no correlation between eyebrows and the number of offspring. As far as your second point, 3% is enormous. But, in any case, the problem is a failure to appreciate that there is a 'noise' threshold below which a probabilistic benefit will have no effect. That is, the length of my pinky may have some miniscule effect on the number of my offspring. But, if the effect is too low, it simply will not have an effect no matter how many millions of generations go by; the randomness of life will swamp it out. To put it in information theory terms, the signal would be indistinguishable from the noise.

toasterlovin 9y ago
Thanks for pushing back, I think we all come to greater understanding through argument (the good kind, not yelling at each other!). In that spirit, here's the next volley: > I disagree. Not every trait has something to do with conferring a benefit. Many traits are simply random artifacts of an exceedingly complex dynamic system. As I said previously, given how complicated of a feature eyebrows are (they have a skeletal component, hair, and muscles which contribute in complex ways to facial expressions), there is no plausible way the existence of eyebrows is due to random variation. Eyebrows would require a whole bunch of very specific mutations to occur at once and mutations are rare. The specific form that people's eyebrows take probably has a fair degree of randomness, but that eyebrows exist at all cannot be due to chance. Further, every single person has eyebrows. If whether or not a person had eyebrows were truly of no consequence to genetic fitness, some people would have them and other wouldn't. > But, it would be reasonable to expect data to back it up. This argument goes both ways. As you say, I have no numbers to show that eyebrows are under selection, but you have no numbers showing that they are not. But your position is worse than that, since you are lacking a plausible explanation for how eyebrows can even exist, given how complicated they are anatomically, without having been selected for. > In my experience, I've seen no correlation between eyebrows and the number of offspring. That's not entirely true. After all, only people with eyebrows have children. :P I am only party kidding about that, btw. Per my previous point, the fact that everyone has eyebrows means that they contributed somehow to people having children. But more seriously: surely you can agree that eyebrows have an impact on attractiveness. After all, a great many people, both male and female, pluck, shape, thin, or color their eyebrows. And surely you can agree that attractiveness at one point was linked to reproductive success (though I agree that it probably has a limited correlation in modern life)? > As far as your second point, 3% is enormous. But, in any case, the problem is a failure to appreciate that there is a 'noise' threshold below which a probabilistic benefit will have no effect. That is, the length of my pinky may have some miniscule effect on the number of my offspring. But, if the effect is too low, it simply will not have an effect no matter how many millions of generations go by; the randomness of life will swamp it out. To put it in information theory terms, the signal would be indistinguishable from the noise. If you make the change in outcome 0.3%, I'm showing that it takes 1,500 generations for for the offspring of the starting 1% subpopulation to reach 50% of the total population. That is all things being equal, etc., etc., but still not very long in evolutionary terms. The thing about evolution is that it acts on gene frequencies in populations. That allows the effectiveness of very minor changes in genetic fitness to be assayed over time. And the larger the population, the more precise the assay is.
- seszett 9y ago
  On the topic of eyebrows, many mammals (maybe most?) also have some kind of special hair above their eyes. Those of cats are very noticeable, dogs also have muscles to move them (though it might have been influenced by humans), seals, otters, hares, all kinds of very diverse animals have something that is analogue to eyebrows, which makes it very unlikely that it would just be a random feature on humans. But it also means it might not have appeared for a specific reason in humans. It might very well have just been there and useless (but not detrimental) at one point, then used for something.
smallnamespace 9y ago
> In my experience, I've seen no correlation between eyebrows and the number of offspring. Many people pay money to disagree with that assessment, at least according to sales of eyebrow pluckers, waxers, and makeup kits that are specifically designed to make it more attractive. Either those people are wasting their time (which needs explanation, since over time people who waste their time and money on things that don't aid reproductive success should be selected away). If it does matters to their reproductive success, then it reflects either cultural or a deeper preference. Personally, I have heard people comment about people who either lack eyebrows (usually through some stupid prank or accident) or have very thick eyebrows. Not having eyebrows definitely interferes with facial signaling, and we signal quite a bit through eye contact. 'The eyes are the windows to the soul'. The eyebrows frame them.
shaki-dora 9y ago
> there is a 'noise' threshold below which a probabilistic benefit will have no effect. [I]t simply will not have an effect no matter how many millions of generations go by We've arrived at a circle in this thread, considering the eyebrow example was initially offered to show how even small advantages will, over time, make some phenotype (and genotype) dominant. This is also mathematically true: given a coin with only the most minimal bias, cumulative results of coin tosses will eventually drift far away from 50%/50%. Concerning your empirical observation regarding the evolutionary usefulness of eyebrows: How many people have you seen being clearly impacted (in regards to their offspring) by missing toes, being born with only one kidney, having ears shaped sub-optimally for capturing sound etc...? Because extremely little regarding your body is left to chance. Unless you're one of less than a hundred with a given feature, be assured that it's a variation that, for a significant number of prior generations, has proven to be useful.
- lurquer 9y ago
  You wrote: This is also mathematically true: given a coin with only the most minimal bias, cumulative results of coin tosses will eventually drift far away from 50% This is what troubles me. I understand your point. But, if it takes a trillion years to 'drift away from 50/50' is it meaningful to describe the bias as something other than zero? That is, is there some Plank's Constant kinda-thing for probabilities? The reason this always comes to mind is the absurdly low probabilistic effect on fecundity of, say, a finch having a 4cm beak versus a 4.1cm beak. If the effect is some probability so low that it would take millions of generations to manifest itself, then, in light of the fact that finches were probably single-celled organisms a million generations back, the probability may as well be zero.

toasterlovin 9y ago

Thanks for pushing back, I think we all come to greater understanding through argument (the good kind, not yelling at each other!). In that spirit, here's the next volley: > I disagree. Not every trait has something to do with conferring a benefit. Many traits are simply random artifacts of an exceedingly complex dynamic system. As I said previously, given how complicated of a feature eyebrows are (they have a skeletal component, hair, and muscles which contribute in complex ways to facial expressions), there is no plausible way the existence of eyebrows is due to random variation. Eyebrows would require a whole bunch of very specific mutations to occur at once and mutations are rare. The specific form that people's eyebrows take probably has a fair degree of randomness, but that eyebrows exist at all cannot be due to chance. Further, every single person has eyebrows. If whether or not a person had eyebrows were truly of no consequence to genetic fitness, some people would have them and other wouldn't. > But, it would be reasonable to expect data to back it up. This argument goes both ways. As you say, I have no numbers to show that eyebrows are under selection, but you have no numbers showing that they are not. But your position is worse than that, since you are lacking a plausible explanation for how eyebrows can even exist, given how complicated they are anatomically, without having been selected for. > In my experience, I've seen no correlation between eyebrows and the number of offspring. That's not entirely true. After all, only people with eyebrows have children. :P I am only party kidding about that, btw. Per my previous point, the fact that everyone has eyebrows means that they contributed somehow to people having children. But more seriously: surely you can agree that eyebrows have an impact on attractiveness. After all, a great many people, both male and female, pluck, shape, thin, or color their eyebrows. And surely you can agree that attractiveness at one point was linked to reproductive success (though I agree that it probably has a limited correlation in modern life)? > As far as your second point, 3% is enormous. But, in any case, the problem is a failure to appreciate that there is a 'noise' threshold below which a probabilistic benefit will have no effect. That is, the length of my pinky may have some miniscule effect on the number of my offspring. But, if the effect is too low, it simply will not have an effect no matter how many millions of generations go by; the randomness of life will swamp it out. To put it in information theory terms, the signal would be indistinguishable from the noise. If you make the change in outcome 0.3%, I'm showing that it takes 1,500 generations for for the offspring of the starting 1% subpopulation to reach 50% of the total population. That is all things being equal, etc., etc., but still not very long in evolutionary terms. The thing about evolution is that it acts on gene frequencies in populations. That allows the effectiveness of very minor changes in genetic fitness to be assayed over time. And the larger the population, the more precise the assay is.

seszett 9y ago
On the topic of eyebrows, many mammals (maybe most?) also have some kind of special hair above their eyes. Those of cats are very noticeable, dogs also have muscles to move them (though it might have been influenced by humans), seals, otters, hares, all kinds of very diverse animals have something that is analogue to eyebrows, which makes it very unlikely that it would just be a random feature on humans. But it also means it might not have appeared for a specific reason in humans. It might very well have just been there and useless (but not detrimental) at one point, then used for something.

smallnamespace 9y ago

> In my experience, I've seen no correlation between eyebrows and the number of offspring. Many people pay money to disagree with that assessment, at least according to sales of eyebrow pluckers, waxers, and makeup kits that are specifically designed to make it more attractive. Either those people are wasting their time (which needs explanation, since over time people who waste their time and money on things that don't aid reproductive success should be selected away). If it does matters to their reproductive success, then it reflects either cultural or a deeper preference. Personally, I have heard people comment about people who either lack eyebrows (usually through some stupid prank or accident) or have very thick eyebrows. Not having eyebrows definitely interferes with facial signaling, and we signal quite a bit through eye contact. 'The eyes are the windows to the soul'. The eyebrows frame them.

shaki-dora 9y ago

> there is a 'noise' threshold below which a probabilistic benefit will have no effect. [I]t simply will not have an effect no matter how many millions of generations go by We've arrived at a circle in this thread, considering the eyebrow example was initially offered to show how even small advantages will, over time, make some phenotype (and genotype) dominant. This is also mathematically true: given a coin with only the most minimal bias, cumulative results of coin tosses will eventually drift far away from 50%/50%. Concerning your empirical observation regarding the evolutionary usefulness of eyebrows: How many people have you seen being clearly impacted (in regards to their offspring) by missing toes, being born with only one kidney, having ears shaped sub-optimally for capturing sound etc...? Because extremely little regarding your body is left to chance. Unless you're one of less than a hundred with a given feature, be assured that it's a variation that, for a significant number of prior generations, has proven to be useful.

lurquer 9y ago
You wrote: This is also mathematically true: given a coin with only the most minimal bias, cumulative results of coin tosses will eventually drift far away from 50% This is what troubles me. I understand your point. But, if it takes a trillion years to 'drift away from 50/50' is it meaningful to describe the bias as something other than zero? That is, is there some Plank's Constant kinda-thing for probabilities? The reason this always comes to mind is the absurdly low probabilistic effect on fecundity of, say, a finch having a 4cm beak versus a 4.1cm beak. If the effect is some probability so low that it would take millions of generations to manifest itself, then, in light of the fact that finches were probably single-celled organisms a million generations back, the probability may as well be zero.