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

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.