https://en.wikipedia.org/wiki/Handicap_principle

The handicap principle is a controversial hypothesis, possible confirmed by Alan Grafen. I would like to understand his reasoning. A handicap is a harmful thing, like a peacock's tail, that attracts females precisely because it is harmful. Dawkins uses the following analogy: if two men are running a marathon, one of them has a bag on his shoulders, and they arrive at the same time, then the woman can choose the man with the bag, because her instincts know that he is strong (since he ran fast despite the bag). But this is probably not a correct analogy, because in wildlife such a bag is worn all his life, and is not removed after the demonstration. I will use a simple model. All men are divided into strong and weak, and into drinkers and non-drinkers (four combinations in total). The weak men drink a lot and this makes it very difficult for them to survive. The strong men drink moderately, this also hinders them, but not much. Women don't know if a man is strong or weak, but they know whether he drinks and that he survived. Therefore, if a woman sees a drinking man, she knows that he is more likely to be strong than a non-drinking man. Here is the weakest point - where did this correlation come from, that the weak drink much, and the strong drink a little? You can also suggest that a man stops drinking after the wedding, but somehow it turns out to be strained.

Here the handicap principle is criticized, but I think that the skepticism is not well-argumented:

https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12563

The Steel Man For the Handicap Principle

The core strength of the handicap principle lies in its solution to the evolutionary problem of deception. If mate signaling were cheap, any low-quality individual could fake a "high-quality" signal, rendering the signal useless to choosy mates.

• Guaranteed Honesty via Cost: The high cost of the signal acts as a structural barrier to lying. A weak peacock literally cannot grow a massive, symmetric tail, or if it does, it will quickly be eaten by a predator. Therefore, the signal is a reliable, un-fakeable indicator of underlying genetic health, immune system strength, and vigor.

• Mathematical Validation: While initially dismissed, mathematical biologists like Alan Grafen later proved that the handicap principle is evolutionary stable, provided that the cost of the signal is proportionally higher for a low-quality individual than for a high-quality one.

• Widespread Explanatory Power: It explains otherwise baffling evolutionary traits, such as "stotting" in gazelles (leaping high in the air in front of a cheetah). By deliberately wasting energy, the gazelle signals to the predator: "I am so fast and fit that trying to catch me is a waste of your time."

The Steel Man Against the Handicap Principle

The strongest counterargument is that honesty does not strictly require waste or handicap, and evolutionary selection usually optimizes for efficiency rather than deliberate disadvantage.

• The Efficiency Over Cost Argument (The "Index" Signal): Critics argue many signals are honest simply because they are physically impossible to fake, not because they are a handicap. For example, a large croak from a toad honestly signals large body size because a small toad physically lacks the vocal anatomy. There is no added "handicap" or self-inflicted cost; it is just a direct physical index.

• The "Good Genes" Alternative: Traits can evolve simply because they are direct products of vigor (e.g., bright feathers reflecting a diet free of parasites). The trait is an output of good health, not a strategic hurdle the animal created to prove its health.

• The Viability Paradox: Natural selection ruthlessly penalizes waste. If Mutation A gives a bird high fitness and no tail, and Mutation B gives a bird the same fitness but forces it to drag a heavy tail to prove it, Mutation A should theoretically win out in terms of pure survival efficiency.

---

Which View Is More Likely Valid?

In modern evolutionary biology, the "Against" view—specifically a highly modified, tempered version of the principle—is considered more valid.

While Zahavi’s original idea that waste itself creates honesty was groundbreaking, it has largely been subsumed by broader theories of receiver psychology and index signaling.

Biologists today generally agree that signals are honest because they are physically or physiologically constrained (indices) rather than strategically wasteful (handicaps). When a cost does exist, it is usually viewed as an unavoidable production cost of a high-quality trait, rather than a deliberate self-imposed penalty to "show off."

50 minutes ago, iNow said:

The Steel Man For the Handicap Principle

The core strength of the handicap principle lies in its solution to the evolutionary problem of deception. If mate signaling were cheap, any low-quality individual could fake a "high-quality" signal, rendering the signal useless to choosy mates.

• Guaranteed Honesty via Cost: The high cost of the signal acts as a structural barrier to lying. A weak peacock literally cannot grow a massive, symmetric tail, or if it does, it will quickly be eaten by a predator. Therefore, the signal is a reliable, un-fakeable indicator of underlying genetic health, immune system strength, and vigor.

• Mathematical Validation: While initially dismissed, mathematical biologists like Alan Grafen later proved that the handicap principle is evolutionary stable, provided that the cost of the signal is proportionally higher for a low-quality individual than for a high-quality one.

• Widespread Explanatory Power: It explains otherwise baffling evolutionary traits, such as "stotting" in gazelles (leaping high in the air in front of a cheetah). By deliberately wasting energy, the gazelle signals to the predator: "I am so fast and fit that trying to catch me is a waste of your time."

The Steel Man Against the Handicap Principle

The strongest counterargument is that honesty does not strictly require waste or handicap, and evolutionary selection usually optimizes for efficiency rather than deliberate disadvantage.

• The Efficiency Over Cost Argument (The "Index" Signal): Critics argue many signals are honest simply because they are physically impossible to fake, not because they are a handicap. For example, a large croak from a toad honestly signals large body size because a small toad physically lacks the vocal anatomy. There is no added "handicap" or self-inflicted cost; it is just a direct physical index.

• The "Good Genes" Alternative: Traits can evolve simply because they are direct products of vigor (e.g., bright feathers reflecting a diet free of parasites). The trait is an output of good health, not a strategic hurdle the animal created to prove its health.

• The Viability Paradox: Natural selection ruthlessly penalizes waste. If Mutation A gives a bird high fitness and no tail, and Mutation B gives a bird the same fitness but forces it to drag a heavy tail to prove it, Mutation A should theoretically win out in terms of pure survival efficiency.

---

Which View Is More Likely Valid?

In modern evolutionary biology, the "Against" view—specifically a highly modified, tempered version of the principle—is considered more valid.

While Zahavi’s original idea that waste itself creates honesty was groundbreaking, it has largely been subsumed by broader theories of receiver psychology and index signaling.

Biologists today generally agree that signals are honest because they are physically or physiologically constrained (indices) rather than strategically wasteful (handicaps). When a cost does exist, it is usually viewed as an unavoidable production cost of a high-quality trait, rather than a deliberate self-imposed penalty to "show off."

Steel man?? Did a bot write this or something?

I'm sorry but this whole thread is the reason I find myself logging on and then just going away again more and more frequently.

I know what you mean, @studiot

But in this case I think Limkey is just offering up an 'evolutionary' explanation for his posting style, and the opinions he expresses therein.

8 hours ago, exchemist said:

Steel man?? Did a bot write this or something?

I prompted a system with a direct request to give me the steel man arguments for and against and to then to summarize based on current consensus which is most likely to be correct. In this case, it was Gemini Flash. It aggregated details across hundreds of thousands of content sources on my behalf.

26 minutes ago, MigL said:

I know what you mean, @studiot

But in this case I think Limkey is just offering up an 'evolutionary' explanation for his posting style, and the opinions he expresses therein.

Evolution is about events of change.

In which case Linkey needs to make a proper reasoned argument and explain what difference 'handicap' makes to evolution and why.

Has it ever affected major evolutionary events such as the transition from sea to land, the development of eyes, ears etc ?

Mate selection can only affect events in a very small way, if at all.

And what about all those organisms that do not use sexual reproduction and mating. They are after all the majority of Life and always have been.

Edited September 11Sep 11 by studiot

32 minutes ago, iNow said:

I prompted a system with a direct request to give me the steel man arguments for and against and to then to summarize based on current consensus which is most likely to be correct. In this case, it was Gemini Flash. It aggregated details across hundreds of thousands of content sources on my behalf.

What is meant by “steel man”, then? I think of Stalin.

1 minute ago, exchemist said:

What is meant by “steel man”, then?

A steelman argument is the practice of rebuilding an opponent's point of view into its strongest, most logical, and most persuasive version before attempting to critique or rebut it.

It is the exact opposite of a straw man argument, where you intentionally oversimplify or misrepresent an opposing view to make it easy to knock down. The goal of steelmanning is deep understanding and truth-seeking rather than just winning a debate.

It's an extremely useful tool I use all of the time to come to my own conclusions on an issue or explain the relevant points to others.

9 minutes ago, iNow said:

A steelman argument is the practice of rebuilding an opponent's point of view into its strongest, most logical, and most persuasive version before attempting to critique or rebut it.

It is the exact opposite of a straw man argument, where you intentionally oversimplify or misrepresent an opposing view to make it easy to knock down. The goal of steelmanning is deep understanding and truth-seeking rather than just winning a debate.

It's an extremely useful tool I use all of the time to come to my own conclusions on an issue or explain the relevant points to others.

That’s interesting. Is this a recognised term, then? I have never encountered it before. But then I’m British, where we talk of an Aunt Sally rather than a Straw Man. Perhaps there needs to be an Uncle Frank counterpart or something.😀

Edited September 11Sep 11 by exchemist

yes

and it's especially powerful when using LLMs to analyze and explore an issue

1 hour ago, studiot said:

In which case Linkey needs to make a proper reasoned argument and explain what difference 'handicap' makes to evolution and why.

He attempts to use inane, unsupported arguments, and WAGs ( his 'handicap' ), to boost his exposure and 'popularity' ( his 'evolution' ).
Unfortunately for him and his misguided efforts, one of these days, it may lead to discipline, or even a ban ( his 'extinction' ).

IOW, it was a joke 🙂 .

No empirical support for this hypothesis. Maynard Smith did a good job of showing how honest signals are not costly, as with stotting by gazelles. And Grafen's model doesn't support the handicap principle, either....

The Handicap Principle: how an erroneous hypothesis became a scientific principle - PMC

The most widely cited explanation for the evolution of reliable signals is Zahavi's so‐called Handicap Principle, which proposes that signals are honest because they are costly to produce. Here we provide a critical review of the Handicap Principle ...

pmc.ncbi.nlm.nih.gov

"We show that Grafen's models do not support the handicap hypothesis, although they do support Zahavi's second hypothesis, which proposes that males adjust their investment into the expression of their sexual signals according to their condition and ability to bear the costs (and risks to their survival). Rather than being wasteful over‐investments, honest signals evolve in this scenario because selection favours efficient and optimal investment into signal expression and minimizes signalling costs. This idea is very different from the handicap hypothesis, but it has been widely misinterpreted and equated to the Handicap Principle. "

On 9/11/2026 at 4:52 AM, iNow said:

Biologists today generally agree that signals are honest because they are physically or physiologically constrained (indices) rather than strategically wasteful (handicaps). When a cost does exist, it is usually viewed as an unavoidable production cost of a high-quality trait, rather than a deliberate self-imposed penalty to "show off."

Okay, I'll bite.

This is the non-breeding plumage (both sexes) of the Pin-tailed Whydah, Vidua macroura, a bird that's fairly common in non-built-up areas near my Lagos base.

Come breeding time, the females become a tad duller (bill loses distinctive colour) and they become proper 'little brown jobs'

.

However, the males switch to something altogether different:

They grow a greatly extended tail, perch all day in the most conspicuous place they can find, and take off every ten minutes or so to perform a little aerobatical dance. Their flying capabilities are really hampered in this plumage, and many quickly fall victim to the many small to medium-sized local raptor species.

If there truly was only a nominal penalty to the stronger individuals in this plumage, why would they be so quick to expend more energy in reverting to non-breeding plumage when the females lose interest?

On 9/11/2026 at 7:25 AM, iNow said:

I prompted a system with a direct request to give me the steel man arguments for and against and to then to summarize based on current consensus which is most likely to be correct. In this case, it was Gemini Flash. It aggregated details across hundreds of thousands of content sources on my behalf.

Going forward I encourage to provide such details in the post plus putting in relevant sources as per https://www.scienceforums.net/topic/133848-policy-on-aillm-use-on-sfn/

I am not wearing a mod hat for this post as I am considering whether I should respond to the content of this thread.

35 minutes ago, sethoflagos said:

If there truly was only a nominal penalty to the stronger individuals in this plumage, why would they be so quick to expend more energy in reverting to non-breeding plumage when the females lose interest?

The principle was explained in general terms. Your example is clear and cogent, but represents a specific case that very well could highlight an exception.

My text spoke more of an average or a mean, whereas your text speaks more as an outlier or deviation from that norm.

That’s my initial thought, anyway. I stipulate that I very well may be wrong.

36 minutes ago, CharonY said:

relevant sources as per…

As a member who knew this well before you said it, and who has participated here for decades (?) now specifically because of rules like this one are in place, I encourage you and the team to recognize (begin to accept?) that this rule will only continue getting harder and harder to enforce.

I was feeling lazy responding in a thread created by a community shit stirrer, and TBH I felt it was self-evident that AI was involved in drafting that specific post.

It’s hardly a pattern of behavior from me, so yeah. Enjoy your weekend.

Edited September 12Sep 12 by iNow

On 9/11/2026 at 10:25 AM, iNow said:

yes

and it's especially powerful when using LLMs to analyze and explore an issue

Moderator Note

And explicitly against our rules to do so outside of speculations, and without disclosing it.

2.13 says (emphasis added)

AI-generated content must be clearly marked. Failing to do so will be considered to be plagiarism and posting in bad faith. In other words, you can’t use a chatbot to generate content that we expect a human to have made.

Since LLMs do not generally check for veracity, AI content can only be discussed in Speculations. It can’t be used to support an argument in discussions

I though I had already consigned mate selection to the sidelines of evolution.

At any rate @Linkey has not replied to demonstrate a connection.

Edited September 12Sep 12 by studiot

3 hours ago, sethoflagos said:

They grow a greatly extended tail, perch all day in the most conspicuous place they can find, and take off every ten minutes or so to perform a little aerobatical dance. Their flying capabilities are really hampered in this plumage, and many quickly fall victim to the many small to medium-sized local raptor species.

If there truly was only a nominal penalty to the stronger individuals in this plumage, why would they be so quick to expend more energy in reverting to non-breeding plumage when the females lose interest?

First of all, males are stupid when they show off to impress females.

Second (serious answer) - while seeming prima facie a notable exception to the prevalent interpretation of Grafen's model, I feel there are aspects of these birds courting which aren't spelled out here. E.g. do the silly-plumed actually succumb to raptor predation at higher rate than non-silly ones? Also, how long does the sexual display period last? If it's fairly brief, the species costs might be fairly low in spite of that period of hindered aeronautics. Finally, do we know there's a high energy cost (metabolic?) to shedding the breeding plumage? For those habitat conditions this type of sexual display could be one of the lowest cost options and most efficient way to be seen. This may not be intuitively obvious in this case, but it could be.

Let me paste a fragment of the book of R. Dawkins "Selfish gene". Sorry that the text is very big, and also it is not authentic: it is an auto translation to English of this text in another language.

In the first edition, I wrote, "I don't believe in this theory, although I'm not nearly as confident in the validity of my skepticism as I was when I first heard about it." I'm glad I wrote "although," because Zahavi's theory now seems far more plausible to me than it did when I first expressed that opinion. Several respected theorists have recently begun to take it seriously, including my colleague Alan Grafen, who, as has been noted in print, "has the rather annoying quality of always being right." He has constructed a mathematical model based on Zahavi's statements and claims that it works. And that this is not some fantastical, esoteric parody of Zahavi, like those others have toyed with, but a direct mathematical embodiment of Zahavi's idea. I will consider here Grafen's original ESS model, although he himself is currently working on a full genetic version that should surpass the ESS model in some respects. This does not mean that the ESS model is actually wrong. It is a good approximation, as are essentially all ESS models, including those described in this book.
The handicap principle is potentially applicable to all situations in which individuals attempt to judge the quality of other individuals, but we will limit our consideration to males advertising themselves to females. This situation is chosen for the sake of clarity. Grafen notes that there are at least four approaches to the handicap principle. They can be called the following: 1) qualifying handicap (any male that survives despite his handicap obviously possesses otherwise excellent qualities, so females choose him); 2) revealing handicap (males perform some difficult task to reveal their hidden talents); 3) conditional handicap (only high-quality males develop a handicap); And finally, 4) Grafen's favorite interpretation, which he called the strategic choice handicap (males possess private information about their own qualities, not shared with females, which they use to "decide" whether to develop a given handicap and how significant it should be). Grafen's strategic choice handicap is amenable to analysis using the ESS. It is not based on the prior assumption that the advertising used by males will be expensive or create handicaps. On the contrary, males are free to develop any type of advertising: honest or deceptive, expensive or cheap. But Grafen shows that, given such freedom of choice at the outset, the handicap system may well prove stable.
Grafen proceeded from the following four assumptions. First, males differ in quality. But quality is not some snobbish notion, like frivolous pride in one's old college or fraternity. (I once received a letter from a reader who concluded, "I hope you won't find my letter presumptuous, after all, I am a Balliol alumnus.") Quality, for Grafen, means that there are good and bad males, in the sense that females will benefit genetically if they choose good males as mates and avoid bad ones. "Good" means strong muscles, capable of running fast, finding prey, and building strong nests. We are not talking about the ultimate reproductive success of a male, since this depends on whether a female chooses a given male. Discussing this now would distract us from the core of the matter. It may or may not manifest itself in the model.
Secondly, females cannot directly assess a male's quality and must rely on his advertising. At this stage, we make no assumptions about the honesty of this advertising. Honesty is something else entirely; it may or may not be detected in the modeling, but that's what the model is for. A male might, for example, "grow" padded shoulders to create the illusion of greater size and strength. The model should show us whether such a false signal will be evolutionarily stable or whether natural selection will favor modest, honest, and truthful advertisements.
Third, males, unlike the females who examine them, in a sense "know" their quality and adopt a specific advertising "strategy"—a rule of conditional advertising depending on their quality. As usual, by "know," I don't mean consciously knowing. Males are assumed to have genes that are activated depending on the male's quality (there is reason to believe that this information is not publicly available, since a male's genes are embedded in his biochemistry, meaning that, by their position, they are undoubtedly much more responsive to his quality than a female's genes). Different males choose different rules. For example, one male might follow the rule: "I display a tail whose size is proportional to my true quality." Another might follow the exact opposite rule. This allows natural selection to adjust the rules, favoring males who are genetically programmed to apply different rules. The level of advertising need not be directly proportional to true quality. A male could even choose the opposite rule. We only require that males be programmed to apply some rule to determine their true quality and choose a particular level of advertising based on this (for example, tail or horn size). As for which of the possible rules will ultimately prove stable, this is again one of the problems the model should help solve.

Fourth, females have the ability to create their own rules. In their case, the rules concern the selection of males based on the effectiveness of the latter's advertising (remember that females, or rather their genes, unlike males, do not have information about quality as such). One female, for example, adheres to the rule: "Trust males completely," a second: "Completely ignore male advertising," and a third: "Assume that in reality, everything is exactly the opposite of what the advertising would like you to believe." So, we've assumed the existence of males who differ in the rules by which they link quality to the level of advertising, and females who differ in the rules by which they relate mate choice to the level of advertising. So far, in our reasoning, males can choose any rule linking quality to advertising, and females can choose any rule linking male advertising to their choice. This is somewhat similar to the "Faithful Reveler and Modest Slut" model in that we're looking for an evolutionarily stable rule for males and an evolutionarily stable rule for females, where stability means mutual stability, where each given rule is stable when both it and the other rule are followed. If we can find such a pair of evolutionarily stable rules, we can study them to understand what life would be like in a community consisting of males and females acting according to these rules. More precisely, would this world conform to Zahavi's handicap principle?
Grafen set himself the task of finding such a mutually stable pair of rules. If I were to undertake this task, I would likely have to engage in long and laborious computer modeling. I would feed the computer data on a series of males, each differing in the rules by which they correlate quality with advertising. I would also feed it data on a series of females, each differing in the rules by which they select males based on the advertising levels employed by the latter. Then I would let the males and females "run" around in the computer, colliding with each other, mating when males satisfied the female selection criteria, and passing on their male and female rules to their sons and daughters. Of course, individuals would survive or perish depending on the quality they inherited. As one generation passed, the changing fates of each male and female rule would be reflected in changes in their frequencies in the population. From time to time, I would check the computer to see if any stable mixtures had formed.
This method should work in principle, but there are difficulties in its application. Fortunately, mathematicians can obtain the same results as modeling by setting up a few equations and solving them. This is precisely what Grafen did. I won't present his mathematical calculations or his further assumptions here, but will instead proceed directly to his conclusions. He succeeded in finding a pair of evolutionarily stable rules.
So, on to the main question. Does Grafen's ESS create a world that Zahavi would recognize as a world of handicaps and fairness? The answer is "yes." Grafen established that the existence of an evolutionarily stable world that combines the following properties postulated by Zahavi is indeed possible:
1. Despite the possibility of free strategic choice in the level of advertising, males choose a level that closely matches their true quality, even if this quality turns out to be low. In other words, under the ESS, males behave honestly.
2. Despite the possibility of free strategic choice, when responding to male advertisements, females ultimately choose the "Trust the Male" strategy. Under the ESS, females are justifiably "trusting."
3. Advertising is expensive. In other words, if the effects of quality and attractiveness could somehow be ignored, it would be more profitable for a male not to advertise (thereby saving energy or becoming less noticeable to predators). Advertising is not only expensive – this advertising system is chosen precisely because of its high cost. It is chosen precisely because it actually leads to a decrease in the success of those who use it (all other things being equal).
4. Advertising is more expensive for high-quality males. With the same level of advertising, the risk for a frail male increases more than for a strong one. Low-quality males are exposed to greater risks from expensive advertising than high-quality ones.
These properties, especially the third, are entirely consistent with Zahavi's ideas. Grafen's picture, demonstrating their evolutionary stability under fairly plausible conditions, seems very convincing. But equally compelling are the arguments of Zahavi's critics (whose influence was felt on the first edition of this book), who believed that Zahavi's ideas have no bearing on evolution.

33 minutes ago, TheVat said:

E.g. do the silly-plumed actually succumb to raptor predation at higher rate than non-silly ones?

You're a raptor scanning a sea of two- to three-foot-high grass in (typically) woodland savannah mosaic. Do you go for a) the drab, capable fliers hiding amongst the grass stems that you can't see, or b) the attention seeker in the hi-vis vest perched atop the big stick who flies like a plastic bag in a breeze?

(If you want something a little more authoritative, we're going to have to employ a few field researchers for a while. I do have the contacts if you're still interested....)

54 minutes ago, TheVat said:

Also, how long does the sexual display period last?

Like the other 18 or so species in genus Vidua, they're polygynous brood parasites (which does impact the energy economy) so they synchronise with the breeding season of the host species. I have photographic records for Apr-Jul (Lagos area early wet season) though the full season may well extend beyond that. (Literature gives late wet season as typical for Vidua)

1 hour ago, TheVat said:

Finally, do we know there's a high energy cost (metabolic?) to shedding the breeding plumage?

It's a cost. Keratin and melanin don''t come FOC.

I think brood parasitim (very common in sub-Saharan Africa for some reason) could well make this a special case. the potential reproductive success from defending a suitable territory for just a couple of weeks could far surpass anything a monogamous non-brood-parasite could achieve in a lifetime. All they have to do is turn grass seed into eggs. And Nigeria isn''t short of grass seed.

The closest reference I've been able to get my hands on is COSTS OF SEXUAL ADVERTISING IN THE LEKKING JACKSON'S WIDOWBIRD

This is from the closely related (Superfamily Ploceoidea) genus Euplectes, and is not a brood parasite. Doesn't positively support my assumption of increased predation, but it firms up the plumage cost side of things.

Abstract. Costs of two sexual advertisements, a 20 cm long tail and lek display, were investigated in Jackson's Widowbird (Euplectes jacksoni). Although leks were frequently disturbed by approaching raptors, no predation was recorded. Judging from counts of growth bars, the nuptial tail completes growth in five weeks, and its final length seems to depend equally on growth time and growth rate. A cost of tail formation is inferred from a lower index of body condition (relative body mass) among males in late compared to early stages of tail growth, and from frequent fault bars (translucent bars due to reduced deposition of keratin) in tail feathers. The number and size of faults were larger in the proximal (last formed) half of feathers, and the frequency of faults increased with both feather length and growth rate. A physiological cost of lek attendance and display was indicated by lower condition among full grown courtholders compared to floaters. In two of four seasons, this was also supported by a decline in condition as a function of how long after lek initiation a male was captured. Among all measured males, full grown tail length was positively related to body condition. In a smaller sample of behaviorally observed males this relationship was obscured, while condition instead was negatively related to display rate and lek attendance. Aerodynamic costs of the tail are discussed, as are the possible roles of tail plumes and display as advertisers of male quality

12 hours ago, sethoflagos said:

think brood parasitim (very common in sub-Saharan Africa for some reason) could well make this a special case.

Could be. The whole scenario as you've described does seem to signal robustness (growing massive tail, hauling it around) at considerable cost. The brood parasitism also means a large metabolic investment doesn't have to be followed by a further high-energy phase of nest construction, defense and food gathering. This fits with Grafen's model where high-quality males afford larger displays (peacock model), allowing display receivers ( females) to reliably judge their condition. But I'm not sure any of this allows fakery, which is what (if I'm not losing the thread here) Zahavi was suggesting as possible. Fakery, in the sense of lower quality males making themselves quite weakened and starved in order to do a massive tail display, wouid seem difficult here. If fakery isn't allowed here, then the whole strategy is evolutionarily stable and not supporting of Zahavi. (I think. Not 100% to speed on Zahavi yet, and my Sunday morning strategy is mental flabbiness.)

An analogy of impermissible fakery would be workers who buy a costly education to signal productivity to prospective employers, then are too broke (and have lost all their friends due to endless studying) to move to another city to take the job.

Edited September 13Sep 13 by TheVat

Ok, back to retract as edit window closed. Looks like I misunderstood part of Zahavi, and his theory is one disallowing fakery by lower quality males.

So my other problem with Zahavi remains, which is his contention that the handicap principle is fairly widespread. It looks to me like index signaling is more the norm, where display costs are not that high and often just a result of natural morphology. Secondary sexual traits in humans for example are mostly functional adaptive traits - hunting males develop longer muscular legs and upper body musculature which is impressive to females but also aids hunting. The deep voice mostly is due to larger size. Body hair assists with transpiration, which helps cool a persistence hunter. Big boobs bring bounty to babies. And so on. So a lot of display is also adaptive. IIRC, this was a point stressed by biologists like Maynard Smith. The one area of human sexual display where parameters exceed natural requirements (i.e. a two incher is sufficient for delivering gametes) is fairly low cost.

So peacocks and whydahs could be exceptions, not ordinary demonstrations of a handicap principle.

I think one should step back and contextualize this discussion a bit. It falls under the broader range of sexual selection, i.e. how can be positively selected due to mate selection. I.e., under this umbrella the trait in question also has to be heritable. OP's scenario falls under communication but not really under sexual selection, as it is not established that drinking is a genetically determined trait.

The handicap principle is an attempt to explain how and why sexual selection of certain seemingly unfavourable traits occur. I am not going to repeat the assumptions that have already been discussed but I will point out that the model by Grafen was flawed and rather than deliberately wasting energy to create honest signals, they actually optimize investment based on condition. This explained in the provided paper:

The equations for Grafen's (1990a) strategic signalling model do not stand up to scrutiny either, as they do not support his main handicap conclusions. Conclusions were made about the absolute costs of signalling at the equilibrium, as predicted by Zahavi's handicap hypothesis, but the equations only provide predictions about the marginal costs of signalling. In other words, the second and third conclusions of the main handicap results are incorrect according the equations for the model. Moreover, subsequent investigations have confirmed that these conditions are not the general conditions of honest signalling: (i) Signals need not be costly at the equilibrium to be honest not even under conflict of interest nor under the assumption of costly signalling (Hurd, 1995; Számadó, 1999; Lachmann et al., 2001; Számadó et al., 2019); and (ii) Signals need not be costlier for worse signallers (Getty, 1998a, 2006). Thus, Grafen's model does not offer any predictions about signalling costs at the equilibrium. The reason that Grafen predicted a positive equilibrium cost is due to an external assumption, namely that the equilibrium cost of signals for the worse quality signallers is zero. This may be a biologically realistic assumption, but it is not a necessary aspect of the logic of honest signalling. With this assumption, Grafen excluded all the possible solutions in which the costs of equilibrium signals are zero or negative. Thus, he concluded that costly signalling is an integral part of the logic of honest signalling, as if it follows from his equations, but it is not. This model does not provide a general principle for honest signalling.

58 minutes ago, TheVat said:

It looks to me like index signaling is more the norm

Is there really such a thing as a 'norm' in mate selection? Doesn't it depend where you look? The whydahs and widowbirds typify one norm, yet Ploceidae proper selects via male nest weaving skils - and that is a huge family that includes some of the most populous undomesticated bird species on the planet (eg. Quelea quelea). By sheer numbers, that has some claim to being a norm doesn't it? And where do we place the quid pro quo sexual habits of Bonobos or the murderous male coalition takeovers of lion prides, or the sneaky female mimicry strategy of non-dominant giant cuttlefish etc?

Looks to me more of a behavioural landscape with encampments scattered all over the terrain. A few more densely populated nodes here and there for sure reflecting various locally stable optima. But I'm not seeing anything approaching a one size fits all mechanism here. More like an exercise in behavioural niche partitioning. If there's a way of doing it, something somewhere will be doing it that way.

X-posted with @CharonY