Il fagiano di Darwin

Darwin’s Really Dangerous Idea – The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World – and Us by Richard O. Prum

Problemino epistemologico:

1. Avete una teoria che spiega quasi tutto.

2. Volete spiegare quella parte di realtà che la teoria non spiega. Che fate?

3. Prima opzione: attendete, prima o poi la teoria spiegherà anche cio’ che ora non spiega.

4. Formulate un’ipotesi aggiuntiva che spieghi in modo semplice quel che resta di non spiegato.

5. Considerate la teoria che spiega quasi tutto sbagliata e restate in attesa di una teoria che spieghi tutto.

La prima opzione è quella prescelta dalla maggioranza degli evoluzionisti. La seconda da una minoranza. La terza dai perfezionisti e dai profeti.

Per illustrare al meglio i tre schieramenti la cosa migliore è parlare di uccelli. Di fagiani in particolare. Perché il fagiano è così meraviglioso?

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Ma prima una precisazione doverosa.

La teoria evoluzionista è zeppa di criticità, ci si puo’ opporre a Darwin, basta si mantenga il dovuto rispetto…

… You might think that my contrarian view of the limited power of adaptation by natural selection would mean that I am “over” Darwin, that I am ready to denigrate the cultural/scientific personality cult that surrounds Darwin’s legacy. Quite to the contrary. I hope to celebrate that legacy but also to transform the popular understanding of it by shedding new light on Darwinian ideas that have been neglected, distorted, ignored, and almost forgotten for nearly a century and a half….

Per molti l’idea di pericolosa di Darwin è rappresentata dalla selezione naturale. Ma ne esiste un’altra che turba i sonni di molti, in particolare dei darwinisti: l’idea dell’autonomia del bello

… The philosopher Daniel Dennett referred to evolution by natural selection—the subject of Darwin’s first great book, On the Origin of Species by Means of Natural Selection—as “Darwin’s dangerous idea.” Here I propose that Darwin’s really dangerous idea is the concept of aesthetic evolution by mate choice, which he explored in his second great book, The Descent of Man, and Selection in Relation to Sex…

Per Darwin la selezione sessuale limita quella naturale e spiega cio’ che la selezione naturale non spiega, per esempio certi ornamenti dei volatili…

… Darwinian mate choice really is dangerous—to the neo-Darwinists—because it acknowledges that there are limits to the power of natural selection as an evolutionary force and as a scientific explanation of the biological world. Natural selection cannot be the only dynamic at work in evolution, Darwin maintained in Descent, because it cannot fully account for the extraordinary diversity of ornament we see in the biological world…

Darwin passò molti momenti tristi contemplando la lunga coda di certi uccelli

… “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!” Because the extravagance of its design seemed of no survival value whatsoever…

Darwin è il miglior apostata di se stesso…

… The insight he eventually arrived at, that there was another evolutionary force at work, was considered an unforgivable apostasy by Darwin’s orthodox adaptationist followers….

L’idea pericolosa di Darwin è stata attaccata da molti nel tentativo di ridurre la selezione sessuale alla selezione naturale…

… Aesthetic evolution by mate choice is an idea so dangerous that it had to be laundered out of Darwinism itself in order to preserve the omnipotence of the explanatory power of natural selection…

Ricordiamo per un attimo le due grandi scoperte di Darwin…

… the two great biological discoveries he revealed in Origin: the mechanism of evolution by natural selection, and the concept that all organisms are historically descended from a single common ancestor and thus related to one another in a “great Tree of Life.”…

Nel difendere l’evoluzionismo Darwin incontrava tre problemi. Primo: non avendo una teoria del genoma non riusciva a spiegare l’ereditarietà

… In confronting the fierce attacks that were mounted against Origin after its publication, Darwin had three gnawing problems. The first problem was the absence of any working theory of genetics. Not knowing the work of Mendel, Darwin struggled and failed to develop a functioning theory of inheritance…

Secondo problema: l’uomo. Qui Darwin glissava con classe…

… Darwin’s second problem was the evolutionary origin of human beings, human nature, and human diversity…

Terzo problema: la presenza in natura di forme di bellezza gratuita

… Darwin’s third big problem was the origin of impracticable beauty. If natural selection was driven by the differential survival of heritable variations, what could explain the elaborate beauty of that peacock’s tail that troubled him so much?…

Sul terzo problema, quello che qui ci preme, Darwin mette una toppa: oltre alla selezione naturale esiste la selezione sessuale…

… In 1871, with the publication of The Descent of Man, and Selection in Relation to Sex, Darwin boldly addressed both the problem of human origins and the evolution of beauty. In this book he proposed a second, independent mechanism of evolution—sexual selection—to account for armaments and ornaments, battle and beauty. If the results of natural selection were determined by the differential survival of heritable variations, then the results of sexual selection were determined by their differential sexual…

Primo meccanismo di selezione sessuale: il combattimento per accaparrarsi il partner. Tipico nei maschi…

… Within sexual selection, Darwin envisioned two distinct and potentially opposing evolutionary mechanisms at work. The first mechanism, which he called the law of battle, was the struggle between individuals of one sex…

Secondo meccanismo: il gusto per la bellezza

… second sexual selection mechanism, which he called the taste for the beautiful, concerned the process by which the members of one sex—often female—choose their mates on the basis of their own innate preferences. Darwin hypothesized that mate choice had resulted in the evolution of many of those traits in nature that are so pleasing and beautiful…

La bellezza è al servizio dell’accoppiamento…

… Courage, pugnacity, perseverance, strength and size of body, weapons of all kinds, musical organs, both vocal and instrumental, bright colors, stripes and marks, and ornamental appendages, have all been indirectly gained…through the influence of love and jealousy, through the appreciation of the beautiful…and through the exertion of a choice…

La sex-selection-theory (SST) è una teoria che mette al centro l’estetica.

Strano: Darwin mette la pura estetica al centro: anche noi con il nostro gusto estetico, oltre alla natura (selezione naturale), contribuiamo a decidere le caratteristiche future della specie…

… described the evolutionary origin of beauty in nature as a consequence of the fact that animals had evolved to be beautiful to themselves. What was so radical about this idea was that it positioned organisms—especially female organisms—as active agents in the evolution of their own species. Unlike natural selection, which emerges from external forces in nature, such as competition, predation, climate, and geography, acting on the organism, sexual selection is a potentially independent, self-directed process in which the organisms themselves (mostly female) were in charge…

Ne consegue che anche gli animali posseggono un gusto estetico

… The first implication of Darwin’s language was that animals are choosing among their prospective mates on the basis of judgments about their aesthetic appeal. To many Victorian readers, even those sympathetic to evolution, this was patently absurd. It seemed impossible that animals could make fine aesthetic judgments…

La vera rivoluzione darwiniana: l’utilitarismo spodestato

… By using the words “beauty,” “taste,” “charm,” “appreciate,” “admire,” and “love,” Darwin was suggest… mating preferences could evolve for displays that had no utilitarian value at all to the chooser, only aesthetic value. In short, Darwin hypothesized that beauty evolves primarily because it is pleasurable to the observer…

Mentre il primo Darwin considera la scelta sessuale un mero prolungamento della selezione naturale, in seguito svolta sull’autonomia dell’estetica…

… Darwin’s views on this issue developed over time. In an early discussion of sexual selection in Origin, Darwin wrote, “Amongst many animals, sexual selection will give its aid to ordinary [natural] selection by assuring to the most vigorous and best adaptive of all males the greatest number of offspring.” In other words, in Origin, Darwin saw sexual selection as simply the handmaiden of natural selection, another means of guaranteeing the perpetuation of the most vigorous and best-adapted mates…

Le parole di Darwin sul fagiano sono inequivocabili…

… “The case of the male Argus pheasant is eminently interesting, because it affords good evidence that the most refined beauty may serve as a sexual charm, and for no other purpose [emphasis added].”…

Gusto e tratti estetici coevolvono…

… Another distinctive feature of Darwin’s theory of mate choice was that it was coevolutionary. Darwin hypothesized that the specific display traits and the “standards of beauty” used to select a mate evolved together, mutually influencing and reinforcing each other…

L’evoluzione dipende dal nostro gusto estetico…

… animals are not merely subject to the extrinsic forces of ecological competition, predation, climate, geography, and so on that create natural selection. Rather, animals can play a distinct and vital role in their own evolution through their sexual and social choices…

Autonomia della scelta sessuale, un concetto dirompente…

… autonomy is the capacity of an individual agent to make an informed, independent, and uncoerced decision. So, sexual autonomy is the capacity for an individual organism to exercise an informed, independent, and uncoerced sexual choice about whom to mate with… In Descent, Darwin presented his hypothesis that female sexual autonomy—the taste for the beautiful—is an independent and transformative evolutionary force in the history of life…

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Talmente dirompente che cominciano gli attacchi a Darwin.

L’esempio di Mivart

… the biologist St. George Mivart wrote, Under the head of sexual selection, Darwin put two very distinct processes. One of these consists in the action of superior strength or activity, by which one male succeeds in obtaining possession of mates and in keeping away rivals. This is, undoubtedly, a vera causa; but may be more conveniently reckoned as one kind of “natural selection” than as a branch of “sexual sele…

Mivart nega che gli animali possano avere sensibilità estetica.

Ad ogni modo Darwin è considerato un traditore (di se stesso)…

… Mivart’s review of Descent also established another enduring intellectual trend. He was the very first person to portray Darwin as a traitor to his own great legacy—a traitor to true Darwinism: “The assignment of the law of ‘natural selection’ to a subordinate position is virtually an abandonment of the Darwinian theory; for the one distinguishing feature of that theory was the all-sufficiency of ‘natural selection’ [emphasis added].”…

L’altro grande critico: Alfred Russel Wallace.

Si tenta di marginalizzare l’idea pericolosa di Darwin…

… In contrast to Darwin’s always polite and understated expression of his views, Wallace’s attack on evolution by mate choice grew ever more strident after Darwin’s death and continued until his own death in 1913. Ultimately, Wallace was so successful that the subject of sexual selection was almost completely marginalized and forgotten within evolutionary biology until the 1970s….

Nasce la teoria dell’ornamento come indicatore di qualità (oggi l’ortodossia)…

… Wallace articulates the idea that sexual displays constitute “honest” indicators of quality and condition—an entirely orthodox view in sexual selection today…

Su Darwin prevale Wallace: la bellezza indice di salute e fertilità…

… Wallace was the first to propose the now exceedingly popular BioMatch.com hypothesis, which holds that all beauty provides a rich profile of practical information about the adaptive qualities of potential mates. This view of evolution has become so pervasive that it even found its way into the 2013 Princeton University graduation speech by the Federal Reserve chairman, Ben Bernanke, who admonished the graduates to “remember that physical beauty is evolution’s way of assuring us that the other person doesn’t have too many intestinal parasites.”…

Sorte della SST

… ejected as “needless,” “unnecessary,” and “ineffective.”…

Tutti diventano più darwiniani di Darwin.

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Fu Ronald Fischer, un matematico/biologo, a resuscitare la SST…

… During the century-long dark age of mate choice theory, however, one man did make a fundamental contribution to the field. In a 1915 paper and a 1930 book, Ronald A. Fisher proposed a genetic mechanism for the evolution of mate choice that built on and extended Darwin’s aesthetic view. Unfortunately, however, Fisher’s ideas on sexual selection would be mostly ignored for the next fifty years…

Fischer: a parità del resto il gusto per la bellezza conta

… Fisher permanently reframed the sexual selection debate with a critical observation: Explaining the evolution of sexual ornaments is easy; all other things being equal, display traits should evolve to match the prevailing mating preferences…

Domanda critica: ma come evolve il gusto?

Per Fischer esistono tre fasi: la prima wallaciana

… The first phase, which is solidly Wallacean, holds that preferences initially evolve for traits that are honest and accurate indices of health, vigor, and survival ability…

Nella seconda fase il gusto si rende indipendente dalla selezione naturale…

… But then, after the origin of mating preference, Fisher hypothesized in his second-phase model, the very existence of mate choice would unhinge the display trait from its original honest, quality information by creating a new, unpredictable, aesthetically driven evolutionary force: sexual attraction to the trait itself. When the honest indicator trait becomes disconnected from its correlation with quality, that doesn’t make the trait any less attractive to a potential mate; it will continue to evolve and to be elaborated merely because it is preferred…

Nella terza fase si entra in una coevoluzione tra gusto e tratti estetici esibiti…

… Fisher hypothesized that a positive feedback loop between the sexual ornament and the mating preference for that ornament will evolve through genetic covariation (that is, correlated genetic variation) between the two…

Nel modello di Fischer la selezione sessuale si auto-rinforza: più un colore piace, più si trasmette alla prole.

Fischer recupera quindi il concetto chiave di autonomia della bellezza…

… Fisher asserted that mating preferences do not continue to evolve because the particular male that the female chooses is any better than any other male. In fact, sexually successful males could sometimes evolve to be worse at survival or poorer in health or condition…

L’analogia con la moda

… This evolutionary mechanism is rather like high fashion. The difference between successful and unsuccessful clothes is determined not by variation in function or objective quality (really) but by evanescent ideas about what is subjectively appealing—the style of the season…

Si noti che la teoria della selezione sessuale si riafferma in coincidenza con la nascita del movimento femminista: in fondo, nell’accoppiamento, la scelta è quasi sempre della donna: potere alle donne!…

… Around the centennial of Darwin’s Descent of Man, the concept of sexual selection began to return to the evolutionary mainstream. Why did it take so long? Although it would require an extensive historical and sociological study to investigate my hunch, I don’t think it was a coincidence that evolutionary biologists finally began to reconsider mate choice, particularly female mate choice, as a genuine evolutionary phenomenon at precisely that moment when women in the United States and Europe began to organize politically and to protest for equal rights, sexual freedom, and access to birth control. It would be nice to think that the insights from evolutionary biologists had an influence on these positive cultural developments, but unfortunately history shows that the opposite was true…

Lande-Kirkpatrick elaborarò un modello generale che ricomprendesse SST.

Un modello di trade-off in cui la bellezza contasse…

… example, a male may have the optimal tail length for survival (that is, favored by natural selection), but if he is not sexy enough to attract even a single mate (that is, disfavored by sexual selection), he will fail to pass on his genes to the next generation. Likewise, a male may have the perfect tail size for attracting mates (that is, favored by sexual selection), but if he is so sexually extravagant that he cannot survive long enough to attract a single mate (that is, disfavored by natural selection), he will also fail to pass on his genes. Lande and Kirkpatrick confirmed the intuition of Darwin and Fisher that natural and sexual selection on display traits will establish a balance between the two opposing forces. At this equilibrium, the male may still be quite far from the natural selection optimum, but that’s the cost of doing business with sexually autonomous, choosy females…

Sulla fine del secolo XX Wallace torna prepotentemente…

… In the 1970s and 1980s, the chief proponent of the neo-Wallacean view of adaptive mate choice was Amotz Zahavi, a charismatic and energetic Israeli ornithologist with a fierce independent streak…

Per Zahavi la bellezza è un handicap che taluni individui esibiscono per segnalare le loro doti di sopravvivenza…

… To Zahavi, the entire point of any sexual display is that it is a costly burden to the signaler—literally, a handicap. By its very existence, the ornamental handicap demonstrates the superior quality of the signaler because the signaler has been able to survive it In what way was the handicapped male better? To Zahavi, it was clear that he could be better in any imaginable way…

Ma la teoria dell’handicap ha un problema

… Zahavi promoted the handicap principle with a single-minded fervor. But his idea had one big flaw. If the sexual advantage of an ornament is directly proportional to its survival costs, then the two forces will cancel each other out, and neither the costly ornament nor a mating preference for it can evolve. In a 1986 paper boldly titled “The Handicap Mechanism of Sexual Selection Does Not Work,” Mark Kirkpatrick provided a mathematical proof of this evolutionary trap…

Per capirlo in modo divertente basta assistere a questo sketch del Saturday Night Live …

… sketch on Saturday Night Live in the 1970s: JANE CURTIN: And so, with a name like Flucker’s, it’s got to be good. CHEVY CHASE: Hey, hold on a second, I have a jam here called Nose Hair. Now, with a name like Nose Hair, you can imagine how good it must be. MMM MMM!! DAN AYKROYD: Hold it a minute, folks, but are you familiar with a jam called Death Camp? That’s Death Camp! Just look for the barbed wire on the label. With a name like Death Camp, it must be so good it’s incredible! Just amazingly good jam! From there the names got worse and worse. John Belushi promoted a jelly called Dog Vomit, Monkey Pus, and then Chevy Chase returned with yet another new jelly named Painful Rectal Itch. The competition culminated with a jelly whose name was so repulsive it induced nausea and could not be spoken on the air. “So good, it’s sick making!” Jane Curtin proclaimed, before signing off with “Ask for it by name!”…

Se da un lato mi penalizzo e dall’altro mi premio come faccio a migliorare la mia condizione? Conclusione: solo il gusto per la bellezza spiega…

… The Smucker’s principle further demonstrates that Zahavi’s handicap principle is fundamentally incompatible with the aesthetic nature of sexual display. Sexual displays actually evolve because they are attractive, not disgustingly informative or repulsively honest…

Ma nel 1990 Alan Grafen di Oxford rese la teoria del segnale coerente: basta ipotizzare una relazione non lineare tra segnale e abilità effettive e il gioco è fatto…

… Grafen showed mathematically that a nonlinear relationship between display cost and mate quality could salvage the theory. In other words, if lower-quality males pay a proportionally higher cost to grow or display an attractive trait than do higher-quality males, then the handicap could evolve…

Ora abbiamo due teorie coerenti della bellezza. Quale scegliere?…

… Having established a way to salvage handicaps, Grafen then asked how we should decide between two plausible evolutionary alternatives, the Zahavian handicap and the Fisherian runaway as elaborated by Lande and Kirkpatrick…

Uno dice: non resta che buttarsi sull’evidenza empirica. Quale teoria è meglio supporta?

Ma pochi si sono buttati sull’evidenza empirica: nella scelta ha prevalso l’ideologia…

… Grafen’s reasoning struck a chord. Although personal comfort is not a scientifically justifiable criterion, many people, including scientists, do want to believe that the world is filled with “rhyme and reason.” So, even though Grafen merely demonstrated that there were conditions under which the handicap principle could work, he so discredited the Fisherian theory that most evolutionary biologists concluded that the handicap principle not only could work but would work—all the time. If belief in the alternative hypothesis is “wicked,” there’s little choice to make. Adaptive mate choice has dominated the scientific discourse ever since…

Abbiamo una teoria che spiega quasi tutto. Il fatto che non spieghi tutto rende pazzi alcuni ricercatori.

L’idea di introdurre un’ipotesi ad hoc per la parte non spiegata li orripila: quella teoria DEVE spiegare tutto. Se non lo fa ora, lo farà domani.

Un esempio di ideologia: Matt Ridly

… Matt Ridley brought this distinction to vivid life in his 1993 book, The Red Queen: The split between Fisher and Good-genes began to emerge in the 1970s once the fact of female choice had been established to the satisfaction of most. Those of a theoretical or mathematical bent—the pale, eccentric types umbilically attached to their computers—became Fisherians. Field biologists and naturalists—bearded, besweatered… and booted—gradually found themselves to be Good-geners…

Per Ridley chi mette le mani in pasta non puo’ che essere wallaciano, solo i teorici da scrivania credono all’autonomia della bellezza predicata dal Darwin censurato… Ma il suo resoconto è subito contraddetto…

… Ironically, I find that I have been written out of the historical narrative of my own discipline. I have spent cumulative years of my life in tropical forests on multiple continents studying avian courtship displays. I have been as “bearded, besweatered, and booted” as any field biologist. Yet I have also been an ardent and inquisitive “Fisherian” since the mid-1980s. According to the Grafen and Ridley narrative, I do not exist. Neither does Darwin, a naturalist who certainly put in his time in the field. Odder still, neither does Grafen, who is primarily a mathematician. Unfortunately, Ridley’s scenario also eliminates from consideration all female field biologists and naturalists. (Sorry, Jane Goodall and Rosemary Grant!)…

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Per comprendere meglio il corto circuito tra evoluzionismo e bellezza facciamo il “caso Kate Moss”.

La sua magrezza, il suo aspetto macilento, emaciato androgino, curvo, pallido e malaticcio non sono certo il ritratto della salute.

I giornali sono perennemente vogliosi di documentare la sua vita spericolata e le sue esperienze con la droga, probabilmente perché la signorina possiede il phisique du rôle per fare da protagonista in storie del genere.

Eppure, per molti è una dea, la donna più bella del pianeta. Per tutti una ragazza comunque bellissima, la regina delle passerelle.

Perché un tipo del genere ci seduce tanto?

La teoria che ci spiega “quasi tutto” va in crisi nel rispondere.

Chi volesse ridurre la “scelta sessuale” a “selezione naturale” avrebbe qualche difficoltà. Siamo di fronte ad un caso in cui – a quanto pare – il nostro gusto estetico si rende autonomo e non sembra molto interessato a raccogliere informazioni su prosperità e fertilità del soggetto.

Difficile pensare che tale bellezza possa in qualche modo esaltare lo stato di salute della ragazza, semmai il contrario.

Ecco allora che, dovendo rinunciare alla teoria del segnale, si ripiega sulla teoria del controsegnale: con il mio corpo ti segnalo che non ho bisogno di segnalare alcunché.

La mia superiorità è tale che posso permettermi di farlo.

Certa bellezza emergerebbe allora non come segnale ma come controsegnale.

Avete presente quei supermegamanager che vanno in ufficio in maglioncino?

Ebbene, stanno controsegnalando. Chi ci va in giacca e cravatta segnala un certo prestigio ma chi ci va in maglioncino segnala che non ha bisogno si segnalare a chicchessia alcunché. Così facendo, di fatto, si segnala un prestigio anche maggiore.

C’è chi redige un curriculum chilometrico per segnalare le proprie competenze. Di contro che chi scrive solo due parole: vedi Google. Quelle due parole, a prescindere dai link sgranati da Google digitando il nome del candidato, rappresentano un controsegnale che dice: “sono talmente qualificato che non perdo tempo a dimostrartelo con un noioso elenco delle mie esperienze passate, se cerchi prove basta un click e ne avrai a volontà.

Ma la teoria del controsegnale, se unita a quella del segnale, ha un inconveniente: spiega troppo. Anzi, spiega tutto. Spiega qualsiasi cosa, di fatto diventa  inconfutabile.

Dove non funziona la teoria sofisticata del segnale, interviene quella cervellotica del controsegnale. Qualsiasi tipo di bellezza è ridotta a “selezione naturale” a prescindere, non esiste la possibilità di essere contraddetti.

La tua bellezza rinvia alla prosperità? Teoria del segnale. Rinvia alla malattia? Teoria del controsegnale. Tutto il resto sta nel mezzo: un po’ segnale, un po’ controsegnale.

In casi del genere che teoria deve scegliere l’uomo razionale? Quella che dà conto dei fatti in modo cervellotico ma coerente con la nostra conoscenza di fondo (selezione naturale) o quella che dà conto dei fatti in modo più semplice ma che aggiunge un’ipotesi (selezione sessuale) alla nostra teoria di fondo (selezione naturale). Entrambe sono sia inconfutabili che indimostrabili che coerenti con i fatti osservati.

Più sotto propongo una griglia di priorità per una scelta razionale che privilegi la semplicità – e quindi la praticità – alla conoscenza di fondo.

kate-moss-for-calvin-klein-obsession-1993

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I fagiani sono da sempre al centro di queste diatribe evoluzionistiche. Dapprima sono stati invocati dai creazionisti contro Darwin…

… In his 1867 antievolution tract, The Reign of Law, the Duke of Argyll cited the “ball and socket” designs of the Great Argus wing feathers as a sign of God’s hand in creation. Darwin countered that the Great Argus is evidence of the evolution of beauty by mate choice, concluding that “it is undoubtedly a marvelous fact that the female [Great Argus] should possess this almost human degree of taste.”…

Poi dagli evoluzionisti puri: ora non sappiamo spiegare il loro piumaggio, domani sapremo… la teoria non puo’ fallare, se i fatti non la confermano, peggio per i fatti…

… Given his low opinion of the cognitive and aesthetic capacities of female pheasants, Beebe simply could not accept the idea of sexual selection: “It seems impossible to conceive, much as we would like to believe in it, and personally, I should be willing to strain a point here and there to admit this pleasant psychologically aesthetic possibility; but I cannot.” Then how did Beebe explain the evolution of the male Great Argus? He could not. He concluded, “It is one of those cases where we should be brave enough to say, ‘I do not know.’ ” Ironically, a man who spent years of his life tracking down the displays of this fabulously beautiful creature, and many other pheasants, found Darwin’s explanation for its beauty “impossible.”…

Sintetizziamo ancora il disaccordo tra biologi sugli ornamenti dei fagiani…

… What biologists don’t agree on is whether mating preferences evolve for those ornaments that provide consistently honest, practical information—about good genes or direct benefits like health, vigor, cognitive ability, or other attributes that would help the chooser—or whether they are merely meaningless, arbitrary (albeit fabulous) results of coevolutionary fashion. Actually, most biologists are in agreement with the former hypothesis. I am not. More precisely, I think that adaptive mate choice can occur but it is probably rather rare, whereas the mechanisms of mate choice envisioned by Darwin and Fisher, and modeled by Lande and Kirkpatrick, are likely to be nearly ubiquitous…

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Diamo un’occhiata a cosa succede sulle più prestigiose riviste di biologia.

Guardiamo in particolare alle motivazioni con cui viene respinto un articolo scientifico…

… In 1997, I submitted a manuscript to the American Naturalist, a first-class science journal in ecology and evolutionary biology… Through a comparative examination of the display behaviors of multiple species within the group, I described how the males of one of the species, the White-throated Manakins, evolved a novel bill-pointing posture that replaced an ancestral tail-pointing posture that had been a routine part of the standard display repertoire. It was as though evolution had edited out the old posture with a cookie-cutter and pasted in the new one in the same exact position within the behavioral sequence. I proposed that this change was unlikely to have evolved because it provided better information about mate quality—if it did, then all of the manakin species would have evolved it—and more likely to have evolved in response to arbitrary, coevolved aesthetic mate preferences…

Ecco allora la tipica obbiezione (piuttosto assurda)…

… I had not tested whether the bill-pointing White-throated Manakin males were revealing their superior vigor or disease resistance. I responded that standing motionless in one posture as opposed to another was unlikely to be able to communicate any additional information about vigor or genetic quality, unless we were to hypothesize that the tail-pointing posture in the ancestral birds had evolved in order to reveal whether they were infested with butt mites, and the bill-pointing posture must have evolved in order to reveal the possibility of some more recent problem in evolutionary history, such as infestations of throat mites. This seemed unlikely to me, but the reviewers insisted that the burden of proof was on me to demonstrate that the display traits were arbitrary. Of course, this made it impossible to “prove” my point…

In sintesi: ma cosa bisogna dimostrare per dimostrare che esiste un gusto per la bellezza anche tra i fagiani?…

… How many of these adaptive hypotheses, I wondered, would I have to test before I could conclude that any given display trait was arbitrary—that is, that it lacked information about any quality other than its attractiveness?…

Bisogna praticamente dimostrare l’impossibile: ovvero la non validità delle migliaia di ipotesi cervellotiche che un sostenitore del signalling potrebbe inventarsi.

E’ la trappola di Grafen

… Because there would be no end to the creative imaginations of the reviewers, there would be no end to the process of trying to demonstrate that any specific trait is arbitrary. I was trapped… I realized that it was Alan Grafen’s standard of evidence that had put me in this bind: “To believe in the Fisher-Lande process as an explanation of sexual selection without abundant proof is methodologically wicked.”…

Carl Sagan diceva…

… “Extraordinary claims require extraordinary evidence.”…

E prima di lui Pierre-Simon Laplace

… “The weight of evidence for an extraordinary claim must be proportioned to its strangeness.”…

L’abbondanza delle prove richieste dipenderebbe dalla stranezza dell’affermazione fatta…

… Thus, whether Grafen’s abundant proof standard should be invoked depends on our perceptions of the strangeness of the Darwin-Fisher theory of mate choice….

Ma quando un’affermazione è strana? Anche certe cervellotiche ricostruzioni del signalling sono alquanto strane.

E poi: se un’affermazione è in linea con le altre ma non descrive i fatti che ne facciamo? Ce la teniamo perché gli amanti delle teorie complete non la trovano strana?

Una vittima illustre di questa impostazione: Einstein

… Of course, it’s human nature to want to believe in a universe that is rational and orderly. No less a scientist than Albert Einstein backed away from quantum mechanics… In rejecting quantum mechanics, Einstein famously wrote, “God does not play dice.” But eventually quantum mechanics triumphed despite its enduring strangeness, because the predictive power of the theory was too great to ignore…

Ecco allora una griglia di parametri per valutare la bontà di una spiegazione razionale…

… A claim that some proposed law is really a law of nature, is justified (i.e. likely to be true, rendered probable) to the extent to which: (1) it leads us to expect (with accuracy) many and varied events which we observe (and we do not observe any events whose non-occurrence it leads us to expect), (2) what is proposed is simple, (3) it fits well with our background knowledge, (4)  there is no rival law which leads us to expect these events which satisfies criteria (1–3) as well as does our proposed law

Se il criterio della semplicità precede quello della conoscenza di fondo, la spiegazione in termini di gusto prevale sull’idea del signalling: mentre la prima è semplice, la seconda è spesso cervellotica e incompleta.

Pochi osano interpretare la moda con la teoria del signalling, sarebbe estremamente cervellotico, è molto più semplice interpretarla in termine di gusti ondivaghi. I fagiani non hanno certo le facoltà cognitive degli uomini, ma per quanto siano depotenziati è lecito supporre che anche in loro avvenga qualcosa del genere, una specie di esperienza estetica.

***

La scienza procede testando la cosiddetta ipotesi nulla

… When we test a scientific hypothesis, we must compare a conjecture—say, that a specific mechanism is responsible for producing the observations that we have made of the world—with a more general conjecture that nothing special is happening; that is, no specific, or special, explanation is required to account for the observations we have made. In science and statistics, this “nothing special is happening” hypothesis is known as the null hypothesis… Thus, before we can assert that some specific process or mechanism of interest is happening, we must first reject the null hypothesis that nothing special is happening…

Ma questo metodo contiene un’asimmetria: cosa deve testare chi sostiene proprio la tesi dell’ipotesi nulla!…

… Thus, before we can assert that some specific process or mechanism of interest is happening, we must first reject the null hypothesis that nothing special is happening…

Talvolta l’ipotesi nulla è la più sensata da fare.

Tra gli uomini, e anche tra gli scienziati, esiste un bias contro l’ipotesi nulla. Tutto deve essere spiegato…

… Unfortunately, there are fundamental reasons why humans, including professional scientists, are biased toward thinking that something special must be happening. The human brain gets lots of rewards for detecting hard-to-see patterns… in the flow of sensory information and cognitive details. Being able to figure out what’s going on when it’s not obvious is perhaps the most fundamental advantage of intelligence…. Lots of people indulge in their irrational desires for meaningful explanations of our chaotic world…

SST e l’autonomia del gusto estetico non viene confutata. Semplicemente si estende il principio della selezione naturale anche laddove al momento non sembra spiegare alcunché…

… After years of struggling against Grafen’s abundant proof standard, I came to realize that the field of evolutionary biology had become like the financial market news reports. Evolutionary biologists have become convinced that a special kind of rhyme and reason—adaptive mate choice—must be happening everywhere and all the time. Why are they so convinced? When you examine it, it is mostly just a belief that the world must be that way….

L’ipotesi del gusto estetico coincide con l’ipotesi nulla, cosicché non puo’ essere provata per definizione. Ovvero, puo’ essere provata solo confutando le infinite ipotesi alternative…

… If the Lande-Kirkpatrick mechanism is the appropriate null model for evolution of traits and preferences, then it… cannot be proven. Thus, Grafen’s demand for “abundant proof” of the Fisher-Lande process was so rhetorically effective precisely because it demanded the impossible. Checkmate! This was the trap I experienced when I realized that I could never satisfy my reviewers. And this is why, nearly 150 years after The Descent of Man and 25 years after Grafen’s 1990 paper, there are still no generally accepted, textbook examples of arbitrary mate choice. Period. Grafen’s gambit triumphed…. model. In the absence of a null model, adaptive mate choice is unscientifically protected from falsification…

Inquadrando tutto in questo paradigma l’ipotesi adattiva vince sempre a priori. Wallace vince per definizione su Darwin…

… When a trait can be shown to be correlated with good genes or direct benefits, the adaptive model is declared to be correct. When no such correlation is found, the result is interpreted merely as a failure to try hard enough to establish how the adaptive model is correct. In this framework, the ultimate research goal for every young scientist or graduate student is to demonstrate what everyone already knows to be true…

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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