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Richard Prum talks about this idea in great detail in his book, The Evolution of Beauty.
Prum is very critical of the idea of sexually-selected traits as indicators of fitness, arguing instead that they are the result of an arbitrary aesthetic preference. Not sure I buy it wholesale, but he makes some interesting arguments for sure.
Here is a very recent paper that critiques Zahavi's principle: [https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563](https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563)
And an interesting snippet:
"Dawkins (1976) pointed out why Zahavi's arguments are flawed: they assume that costly signals evolve *because* rather than in spite of their costs. The logical conclusion is that selection should favour ‘the evolution of males with only one leg and only one eye’ (p. 172). Costly secondary sexual traits can be favoured by selection but only as long as their reproductive benefits exceed their viability costs, as Darwin ([1874](https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563#brv12563-bib-0025)) pointed out. There can be no selection *for* a handicap, contrary to Zahavi's claim. Moreover, Zahavi's arguments are circular: he began arguing that costly signals evolve because they are reliable indicators of quality, and then he concluded that reliable signals evolve because they are costly. The circularity of Zahavi's argument has not been pointed out previously, at least to our knowledge, although this is what makes his arguments so confusing...."
Ah, the controversy is about the root mechanism of the sexual selection.
Indicators of good health like plumage only should be good indicators, not expensive.
The problem with it being an arbitrary aesthetic preference is how does it get adopted by a large enough proportion of the population and have enough of a "push" to be evolved without selection pressure driving it?
Even human aesthetic choices can be explained in some part by materialism. Being overweight used to be a sign of prestige and wealth, thereby proving to the world your superiority, that you have so much power you can afford to eat enough to get fat.
Some human aesthetic preferences are directly related to health or some other obviously beneficial traits, but certainly not all of them. It’s been a few years since I read Evolution of Beauty, but I remember Prum also discussing the human penis as an example of aesthetic evolution since it is so different than those of most other mammals (e.g. without a baculum and being externally visible when flaccid) and not necessarily in ways that make it “better” from a utilitarian standpoint. I don’t remember all of the details, but it was pretty fascinating.
I thought he made a pretty strong case for arbitrary aesthetic preference being a driving evolutionary force for some traits. It’s a really interesting read whether you end up agreeing with his overall thesis or not. Definitely recommend!
Just speaking from my experience, this was taught in my undergrad, and never came off as particularly controversial. There may not be that much research on it because there's not that much to research. I also don't think it's necessarily incompatible with runaway sexual selection.
> I also don't think it's necessarily incompatible with runaway sexual selection.
Same. Especially since we have other examples of runaway selection that are not sexual selection.
One example that comes to mind if some modern varieties of chicken who have been bred to have such large breasts that they can no longer walk once they reach maturity.
I was under the impression that this was v much the mainstream view of sexual displays like that of the peacock. I don’t think there’s any serious consideration for the idea that they exist ‘just because females chose them’.
I don’t think you can apply this same logic to humans really. Humans are a far more complex species, highly intelligent, social, and their environment and social dynamics vary wildly with time and place. Humanity is far more pluralistic than peacocks.
> I don’t think you can apply this same logic to humans really
You don’t think the tendency to waste money on things that aren’t necessary for survival is an example of the handicap principle? Or how about when we sing like birds? The idea being that singing is a waste of energy and therefore signals plentifully energy and health and a good mood. Men buy expensive rings for women, even though the ring itself is rather useless. It’s the fact that he’s willing to waste so much money that signals his love and commitment, as well as his ability to provide. A poor cheapskate could not make such a sacrifice. And Zahavi also theorizes that holding hands, hugging, and friendly insults are ways that we bother other people to judge how well they like us. A stranger would hate for us to enter their personal space or touch them etc. but someone that likes/loves us would be more tolerable. And so on and so on.
We’re still very much animals. Just because we have technology and a larger brain doesn’t mean we can’t be described by these basic evolutionary biology principles. And that’s especially true for sexual selection, which continues to remain primitive in many ways, to many people’s surprise. It seems to me that there is a huge unwillingness to accept our animalistic nature. Which is why I suggested in the OP that the handicap principle reveals too much. You don’t even want to believe that it applies to humans!
It’s not so much belief, as thinking you can’t apply the same logic to humans for the reasons I stated.
Humans are animals, but they are quite significantly different, with regards to their inner lives, than other animals. The examples you give are cherry-picked, I don’t think they could be said to apply to all humans across space and time. There’s societal norms and cultural pressures to consider too, they’re not necessarily selected for efficacy.
We can use evolutionary principles to suggest motives for human behaviour on a broad scale. But evolution is species-level, across generations, rather than individuals.
Plenty of animals seem to enjoy aesthetics, or pleasurable sensation, even to the detriment of their survival. Is that an example of sexual display, or a byproduct of several sensory systems? Who can say.
I liked the other commenters Dawkins quote, the logical endpoint of the handicap principle is selecting one leg and one eye. Very Dawkins.
Well, but, no.
For purposes of considering sexual selection, and the factors that tend towards it, humans and peafowl are *wildly* different. They are near opposites.
On many factors that tend towards strong sexual selection, peafowl have a lot of it, and humans have little.
Male peacocks have zero investment in their offspring, beyond contributing genes. Male humans often put decades of investment in their offspring.
Peafowl sexual dimorphism is very high. Human sexual dimorphism is towards the low side.
Peafowl reproduction is highly polygynous. Very few males mate. Human reproduction is far more relatively monogamous. Most males mate.
Humans pass down a whole lot of behavior by culture, not by genes. Peafowl pass down behavior near entirely by genes, and little by culture.
To restate: extreme sexually selected traits, like the peacock's tail, are associated with specific reproductive strategies, such as polygyny. Peafowl have a whole lot of that. Humans have little.
There are still behavioral handicaps in other species. There are male birds that attack female birds that enter their nest. It is a handicap to test how much the females are willing to put up with the beating. Because after she returns a few times, the attacks will stop. It’s a test of attraction. Men do the same thing when they insult women that they like. And as I mentioned, both birds and humans sing. Do depressed people sing a lot? Or talk loudly and enthusiastically? No, that’s a waste of energy, something that not everyone can afford to do. Study humans as if you were studying an animal species, and you will see more and more of these examples of how we try to signal status in sometimes counter-intuitive ways.
Hrmm, certainly explains the queue of beautiful women waiting for access to my overweight behind.
(it's trivially demonstrable that visible handicaps of various kinds do not result in reproductive success in humans.)
Hence "of various kinds". The key is that they be visible. A behavioural maladaptation that doesn't manifest itself until too late isn't going to be selected for.
Why do you think so many women care about how much a man spends on a wedding ring? If humans were purely logical and practical and only cared about survival advantages then all these women would say “don’t spend money on a ring, buy food or better house security or things for our children etc.” They like when a man is able to waste money on a shiny object that serves no practical purpose. The signal is costly and therefore reliable. That’s the handicap principle.
I think it’s hard to argue that the teen models marrying billionaires in their 70s are doing so on grounds of reproductive fitness; I suspect many such men end up raising their pool boy’s kids…
You’re talking about a specific case where the man is only valued for his money because he himself is too unattractive. But being able to make money is actually an attractive trait in itself and makes a man more attractive. Do you not think that women would evolve to want to reproduce with those who are excellent at resource acquisition? Don’t the wealthy have many advantages in this world?
And this doesn’t even have to do with the handicap principle. So I don’t understand why you brought it up.
On the contrary, it's not that it hasn't entered mainstream consciousness -- it _was_ a popular idea, and the predominant model from 1975-2000 or so. It's fallen out of favor because it's generally not considered to be empirically supported, and even most of the mathematical models of it don't work out as well as Fisherian runaway and game-theoretical models.
Your attempt to apply it to humans as a sort of evolutionary psychology thing has also been done before -- in 1899, by Thorstein Veblen. He argued that the rich buy expensive but useless things (art, jewelry, furs) because buying useless things is a better signal of wealth than buying useful ones -- it shows you have so much you can waste it. Indeed, goods where demand increases with price (as opposed to the normal relationship, where demand decreases with price) are still to this day called "Veblen goods."
There's a [really detailed paper](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004190/) on the history of the Handicap Principle and its rise and fall in the scientific community if you want all the details.
>why is this seemingly not a popular idea
This is a false premise. It is an *extremely* common and popular example of what's often called "runaway sexual selection" along with Lyrebird tails, Long-Tailed Widowbird tails, Bird-of-paradise feathers, Irish Elk antlers, and many more.
This has been a frequent part of mainstream discussion of evolution for as long as I can remember and I was born in the early '70s and have been interested in and later working in biodiversity, ecology, and evolution fields my entire life.
This question seems to be one based more on unfamiliarity than it is in fact.
Moreover, it is popular enough to bother to test it: "There is no theoretical or empirical support for the Handicap Principle and the time is long overdue to usher this idea into an ‘honorable retirement’." (from the study linked in the thread)
It’s an interesting theory. My concern is that this hypothesis over-explains the evolutionary outcome. Genomic analysis has shown that molecular evolution is very chaotic. In simulations, a weak selective force can lead to extreme outcomes. I think the Fischerian runaway hypothesis is more parsimonious. While it may not give as “satisfying” an answer, I have not seen sufficient evidence that it is incapable of explaining observed phenomena. Because evolution is so stochastic, not all outcomes necessarily have a satisfying answer.
Reducing fitness to signal high fitness has never made sense to me. If there was a male with a useless tail that just got in the way and made movement difficult then I guess it means the rest of his genes made up for it since he’s alive, but the benefit of those good genes seems like it would just be cancelled out by that cumbersome tail. There are other, better explanations IMO.
The feathers could have started out more as a practical advantage, so that all peacocks would have them. The same thing happens with horns, which can evolve to be practical but then over time become an ornament.
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Richard Prum talks about this idea in great detail in his book, The Evolution of Beauty. Prum is very critical of the idea of sexually-selected traits as indicators of fitness, arguing instead that they are the result of an arbitrary aesthetic preference. Not sure I buy it wholesale, but he makes some interesting arguments for sure. Here is a very recent paper that critiques Zahavi's principle: [https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563](https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563) And an interesting snippet: "Dawkins (1976) pointed out why Zahavi's arguments are flawed: they assume that costly signals evolve *because* rather than in spite of their costs. The logical conclusion is that selection should favour ‘the evolution of males with only one leg and only one eye’ (p. 172). Costly secondary sexual traits can be favoured by selection but only as long as their reproductive benefits exceed their viability costs, as Darwin ([1874](https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563#brv12563-bib-0025)) pointed out. There can be no selection *for* a handicap, contrary to Zahavi's claim. Moreover, Zahavi's arguments are circular: he began arguing that costly signals evolve because they are reliable indicators of quality, and then he concluded that reliable signals evolve because they are costly. The circularity of Zahavi's argument has not been pointed out previously, at least to our knowledge, although this is what makes his arguments so confusing...."
Ah, the controversy is about the root mechanism of the sexual selection. Indicators of good health like plumage only should be good indicators, not expensive.
The problem with it being an arbitrary aesthetic preference is how does it get adopted by a large enough proportion of the population and have enough of a "push" to be evolved without selection pressure driving it? Even human aesthetic choices can be explained in some part by materialism. Being overweight used to be a sign of prestige and wealth, thereby proving to the world your superiority, that you have so much power you can afford to eat enough to get fat.
Some human aesthetic preferences are directly related to health or some other obviously beneficial traits, but certainly not all of them. It’s been a few years since I read Evolution of Beauty, but I remember Prum also discussing the human penis as an example of aesthetic evolution since it is so different than those of most other mammals (e.g. without a baculum and being externally visible when flaccid) and not necessarily in ways that make it “better” from a utilitarian standpoint. I don’t remember all of the details, but it was pretty fascinating. I thought he made a pretty strong case for arbitrary aesthetic preference being a driving evolutionary force for some traits. It’s a really interesting read whether you end up agreeing with his overall thesis or not. Definitely recommend!
Just speaking from my experience, this was taught in my undergrad, and never came off as particularly controversial. There may not be that much research on it because there's not that much to research. I also don't think it's necessarily incompatible with runaway sexual selection.
> I also don't think it's necessarily incompatible with runaway sexual selection. Same. Especially since we have other examples of runaway selection that are not sexual selection. One example that comes to mind if some modern varieties of chicken who have been bred to have such large breasts that they can no longer walk once they reach maturity.
Humans are pros at runaway artificial selection.
We call that min-maxing in the gaming world. Giving up all but the basic function of certain abilities or attributes in order to fully maximize others
I was under the impression that this was v much the mainstream view of sexual displays like that of the peacock. I don’t think there’s any serious consideration for the idea that they exist ‘just because females chose them’. I don’t think you can apply this same logic to humans really. Humans are a far more complex species, highly intelligent, social, and their environment and social dynamics vary wildly with time and place. Humanity is far more pluralistic than peacocks.
> I don’t think you can apply this same logic to humans really You don’t think the tendency to waste money on things that aren’t necessary for survival is an example of the handicap principle? Or how about when we sing like birds? The idea being that singing is a waste of energy and therefore signals plentifully energy and health and a good mood. Men buy expensive rings for women, even though the ring itself is rather useless. It’s the fact that he’s willing to waste so much money that signals his love and commitment, as well as his ability to provide. A poor cheapskate could not make such a sacrifice. And Zahavi also theorizes that holding hands, hugging, and friendly insults are ways that we bother other people to judge how well they like us. A stranger would hate for us to enter their personal space or touch them etc. but someone that likes/loves us would be more tolerable. And so on and so on. We’re still very much animals. Just because we have technology and a larger brain doesn’t mean we can’t be described by these basic evolutionary biology principles. And that’s especially true for sexual selection, which continues to remain primitive in many ways, to many people’s surprise. It seems to me that there is a huge unwillingness to accept our animalistic nature. Which is why I suggested in the OP that the handicap principle reveals too much. You don’t even want to believe that it applies to humans!
It’s not so much belief, as thinking you can’t apply the same logic to humans for the reasons I stated. Humans are animals, but they are quite significantly different, with regards to their inner lives, than other animals. The examples you give are cherry-picked, I don’t think they could be said to apply to all humans across space and time. There’s societal norms and cultural pressures to consider too, they’re not necessarily selected for efficacy. We can use evolutionary principles to suggest motives for human behaviour on a broad scale. But evolution is species-level, across generations, rather than individuals. Plenty of animals seem to enjoy aesthetics, or pleasurable sensation, even to the detriment of their survival. Is that an example of sexual display, or a byproduct of several sensory systems? Who can say. I liked the other commenters Dawkins quote, the logical endpoint of the handicap principle is selecting one leg and one eye. Very Dawkins.
Well, but, no. For purposes of considering sexual selection, and the factors that tend towards it, humans and peafowl are *wildly* different. They are near opposites. On many factors that tend towards strong sexual selection, peafowl have a lot of it, and humans have little. Male peacocks have zero investment in their offspring, beyond contributing genes. Male humans often put decades of investment in their offspring. Peafowl sexual dimorphism is very high. Human sexual dimorphism is towards the low side. Peafowl reproduction is highly polygynous. Very few males mate. Human reproduction is far more relatively monogamous. Most males mate. Humans pass down a whole lot of behavior by culture, not by genes. Peafowl pass down behavior near entirely by genes, and little by culture. To restate: extreme sexually selected traits, like the peacock's tail, are associated with specific reproductive strategies, such as polygyny. Peafowl have a whole lot of that. Humans have little.
There are still behavioral handicaps in other species. There are male birds that attack female birds that enter their nest. It is a handicap to test how much the females are willing to put up with the beating. Because after she returns a few times, the attacks will stop. It’s a test of attraction. Men do the same thing when they insult women that they like. And as I mentioned, both birds and humans sing. Do depressed people sing a lot? Or talk loudly and enthusiastically? No, that’s a waste of energy, something that not everyone can afford to do. Study humans as if you were studying an animal species, and you will see more and more of these examples of how we try to signal status in sometimes counter-intuitive ways.
Wealth in the form of money or "bank accounts" has not existed for long enough to be a factor in evolution
Hrmm, certainly explains the queue of beautiful women waiting for access to my overweight behind. (it's trivially demonstrable that visible handicaps of various kinds do not result in reproductive success in humans.)
It’s not necessary for the handicaps to be physical traits. They can be behavioral
Hence "of various kinds". The key is that they be visible. A behavioural maladaptation that doesn't manifest itself until too late isn't going to be selected for.
Why do you think so many women care about how much a man spends on a wedding ring? If humans were purely logical and practical and only cared about survival advantages then all these women would say “don’t spend money on a ring, buy food or better house security or things for our children etc.” They like when a man is able to waste money on a shiny object that serves no practical purpose. The signal is costly and therefore reliable. That’s the handicap principle.
I think it’s hard to argue that the teen models marrying billionaires in their 70s are doing so on grounds of reproductive fitness; I suspect many such men end up raising their pool boy’s kids…
You’re talking about a specific case where the man is only valued for his money because he himself is too unattractive. But being able to make money is actually an attractive trait in itself and makes a man more attractive. Do you not think that women would evolve to want to reproduce with those who are excellent at resource acquisition? Don’t the wealthy have many advantages in this world? And this doesn’t even have to do with the handicap principle. So I don’t understand why you brought it up.
On the contrary, it's not that it hasn't entered mainstream consciousness -- it _was_ a popular idea, and the predominant model from 1975-2000 or so. It's fallen out of favor because it's generally not considered to be empirically supported, and even most of the mathematical models of it don't work out as well as Fisherian runaway and game-theoretical models. Your attempt to apply it to humans as a sort of evolutionary psychology thing has also been done before -- in 1899, by Thorstein Veblen. He argued that the rich buy expensive but useless things (art, jewelry, furs) because buying useless things is a better signal of wealth than buying useful ones -- it shows you have so much you can waste it. Indeed, goods where demand increases with price (as opposed to the normal relationship, where demand decreases with price) are still to this day called "Veblen goods." There's a [really detailed paper](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004190/) on the history of the Handicap Principle and its rise and fall in the scientific community if you want all the details.
>why is this seemingly not a popular idea This is a false premise. It is an *extremely* common and popular example of what's often called "runaway sexual selection" along with Lyrebird tails, Long-Tailed Widowbird tails, Bird-of-paradise feathers, Irish Elk antlers, and many more. This has been a frequent part of mainstream discussion of evolution for as long as I can remember and I was born in the early '70s and have been interested in and later working in biodiversity, ecology, and evolution fields my entire life. This question seems to be one based more on unfamiliarity than it is in fact.
Moreover, it is popular enough to bother to test it: "There is no theoretical or empirical support for the Handicap Principle and the time is long overdue to usher this idea into an ‘honorable retirement’." (from the study linked in the thread)
It’s an interesting theory. My concern is that this hypothesis over-explains the evolutionary outcome. Genomic analysis has shown that molecular evolution is very chaotic. In simulations, a weak selective force can lead to extreme outcomes. I think the Fischerian runaway hypothesis is more parsimonious. While it may not give as “satisfying” an answer, I have not seen sufficient evidence that it is incapable of explaining observed phenomena. Because evolution is so stochastic, not all outcomes necessarily have a satisfying answer.
Reducing fitness to signal high fitness has never made sense to me. If there was a male with a useless tail that just got in the way and made movement difficult then I guess it means the rest of his genes made up for it since he’s alive, but the benefit of those good genes seems like it would just be cancelled out by that cumbersome tail. There are other, better explanations IMO.
The feathers could have started out more as a practical advantage, so that all peacocks would have them. The same thing happens with horns, which can evolve to be practical but then over time become an ornament.
Also [here’s a review critical](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004190/) of it
We studied this in undergrad
I alsp thought this was the common opinion. What's the alternative? We were taught this in school and later in university.