Sbagliando s'impera

Wilson, Edward O. (2012). The Social Conquest of Earth. New York: W. W. Norton. 2012. ISBN 9780871404138. Pagine 330. 15,24 €

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Edward O. Wilson è un vecchio signore del Sud (è nato a Birmingham in Alabama il 10 giugno 1929 – a proposito, auguri in ritardo!). Ne abbiamo parlato più volte su questo blog, da ultimo qui (mi pare), ma soprattutto recensendo il suo unico romanzo, Anthill. Purtroppo, ho letto gli altri suoi libri in epoca ante-blog e quindi non li ho recensiti qui (né da nessuna altra parte, perché non mi imponevo quella forma di disciplina che il blog ha portato con sé).

Ho però raccontato, nella recensione al romanzo, che questo vecchio signore del Sud dall’aria serena è stato al centro di furiose polemiche per il suo Sociobiology. The New Synthesis del 1975. Adesso è di nuovo al centro delle polemiche per questo libro che, nelle sue intenzioni, voleva essere una sintesi dei suoi studi sugli organismi eu-sociali – come li chiama lui stesso – cioè gli insetti sociali e gli umani.

Il problema è che per fare questo, Wilson ha bisogno di rigettare la teoria della kin selection originariamente formulata da Hamilton e cui Wilson stesso aveva aderito all’epoca di Sociobiology e aderire invece a quella della group selection, vivacemente e ferocemente avversata dai darwiniani puri e duri.

Sorgono spontanee 2 domande:

1. chi ha ragione nella disputa, Wilson o i suoi oppositori? o meglio: è sostenibile una teoria della group selection? e quella della kin selection è davvero stata smentita?
2. nell’ipotesi che il libro di Wilson sia affetto da errori teorici gravi, vale la pena egualmente di leggerlo?

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Sulla prima questione, per affrontarla senza troppi tecnicismi, penso sia opportuno partire dal punto specifico del libro di Wilson in cui l’autore abbandona la prospettiva della kin selection:

For almost half a century, it has been popular among serious scientists seeking a naturalistic explanation for the origin of humanity, I among them, to invoke kin selection as a key dynamical force of human evolution. […]
Unfortunately for this perception, the foundations of the general theory of inclusive fitness based on the assumptions of kin selection have crumbled, while evidence for it has grown equivocal at best. The beautiful theory never worked well anyway, and now it has collapsed.
A new theory of eusocial evolution, drawn in part from my collaboration with the theoretical biologists Martin Nowak and Corina Tarnita, and in part from the work of other researchers, provides separate accounts for the origin of eusocial insects on the one hand and the origin of human societies on the other. [859-866. Il riferimento è come di consueto alle posizioni sul Kindle]

Naturalmente, abbandonare una posizione cui si era aderito in passato è perfettamente lecito: solo gli imbecilli, si dice, restano attaccati alle proprie idee contro ogni evidenza come patelle agli scogli. Quello che però Wilson non dice – e questo io lo trovo particolarmente grave in un libro rivolto al pubblico non specialistico – è che l’articolo di Nowak, Tarnita & Wilson “The evolution of eusociality“, pubblicato nel 2010 sul numero 466 di Nature, ha suscitato un vespaio di polemiche: sia perché l’articolo non sarebbe transitato attraverso il normale processo di peer review grazie all’autorevolezza di Wilson (succede anche a Nature, evidentemente), sia perché le conclusioni cui giunge sono state contestate da circa 150 scienziati in 5 risposte al paper di Nowak, Tarnita & Wilson. Quello che questi scienziati sostengono è che la teoria della kin selection e della inclusive fitness sono tutt’altro che crollate, come invece Wilson dà per assodato.

Questo spiega ampiamente perché The Social Conquest of Earth sia stato accolto con molte critiche e poco entusiasmo. Ne riassumo qualcuna di quelle con cui sono entrato in contatto.

Michael Gazzaniga sul Wall Street Journal del 6 aprile 2012 (Evolution Revolution) paragona la delusione provata leggendo quest’ultima prova di Wilson con quella che gli appassionati di jazz sono destinati a provare, prima o poi, per i loro beniamini:

At a certain point in their careers, great jazz musicians are almost bound to disappoint their fans. Think of John Coltrane venturing into free jazz in the late 1960s or Miles Davis going electric a few years later. The vision that made them great the first time pushes them into new territory, and the magnitude of their early accomplishments – and the number of admirers they have attracted – makes their public’s sense of betrayal all the more bitter. All they can do is keep playing, undaunted by the dissent.

La metafora jazzistica è anche funzionale a notare che (purtroppo) Wilson procede per improvvisazione, per grandi pennellate, nascondendoci il dettaglio del ragionamento che lo ha portato ad abbandonare il modello della inclusive fitness. ed evitando di rispondere alle critiche dei 150 scienziati che hanno contestato il suo modello su Nature.

Jazz artists improvise. Mr. Wilson does too as he goes through his argument in “The Social Conquest of Earth.” I say “improvise” because he chooses not to give the reader the complete story, properly annotated with references that would capture the huge controversies that accompany almost all the facts he reviews. […] While Mr. Wilson may have tired of all the rancor, it would have been intriguing to have his full account of how he arrived at his conclusions.

Jennifer Schuessler sul New York Times dell’8 aprile, più che una recensione, ci offre un ritratto di Edward O. Wilson (Lessons From Ants to Grasp Humanity) che non rifugge però dal riassumere i termini della controversia:

If no one is quite ready to dump a pitcher of water over Dr. Wilson’s head, many colleagues are mystified and dismayed by his late-life embrace of group selection – a highly controversial notion among biologists – and rejection of the kin-selection theory that he helped popularize in “Sociobiology.”
“ ‘Sociobiology’ is still a very great book, and now he’s trashing it all,” said Jerry Coyne, a professor of ecology and evolution at the University of Chicago. “It’s crazy.” Dr. Coyne was one of more than 150 scientists who signed four letters published last spring in the journal Nature criticizing a 2010 paper by Dr. Wilson, written with the mathematicians Martin A. Nowak and Corina E. Tarnita, outlining his group-selection arguments.
But Dr. Wilson, putting on a fleece vest under his professorial green tweed jacket in preparation for a rainy walk through Central Park, seemed unruffled by the fracas, which is only passingly acknowledged in the new book. “I don’t mind it,” he said of the criticism, adding that he had full confidence in his co-authors’ complex math. “I actually expect it for any important change. No pain, no gain.”

Un concetto simile era già stato espresso da Wilson in un articolo di Jonah Lehrer comparso sul numero del 5 marzo 2012 del New Yorker (Kin and Kind. A fight about the genetics of altruism):

“I’ve always been an ambitious synthesizer,” he told me. “But I’m now wise enough to know the limitations of that approach.” These days, he regards the books that made him famous – ”Sociobiology” and “On Human Nature” (1979) – as flawed accounts of evolution, marred by their uncritical embrace of inclusive fitness.

La recensione di Steven Mithen – appena pubblicata su The New York Review of Books, nel numero datato 21 giugno 2012 (How Fit Is E.O. Wilson’s Evolution?) – ha il pregio, secondo me, di mettere chiaramente in luce le responsabilità dello scienziato che scrive per il vasto pubblico e non per gli specialisti e i colleghi:

My greater concern is about the responsibility of the scientist writing for the general reader, especially a scientist of Wilson’s academic reputation. Such readers, the type targeted by Wilson and his publisher, may never have heard of Nature and would be unlikely to consult endnotes. Such readers, owing to his failure to acknowledge the extent of opposition to his views, would be entirely misled into thinking that Wilson had indeed “demonstrated that inclusive fitness theory, often called kin selection theory, is both mathematically and biologically incorrect.”
[…] I cannot avoid the impression that the manner in which Wilson presents his views verges toward polemic rather than providing a responsible work of popular science.

Ho lasciato di proposito per ultima la recensione più completa, e anche la più feroce: quella di Richard Dawkins pubblicata su Prospect del 24 maggio 2012 (The descent of Edward Wilson. A new book on evolution by a great biologist makes a slew of mistakes). Suggerirei, se il vostro inglese lo consente (ma se non lo consentisse probabilmente non leggereste questo blog), di leggere l’articolo di Dawkins nella sua interezza, per almeno 3 motivi:

1. Dawkins scrive bene e in modo molto chiaro e articolato;
2. Dawkins è un polemista pungente ed efficacissimo (a tratti uno prova anche un po’ pena per il malcapitato Wilson);
3. La spiegazione di Dawkins dei motivi per cui ritiene corretta la teoria della kin selection ed erronea quella della group selection.

Per i più pigri (e per mio gusto) metterò qui i punti essenziali:

[I]it was a good idea to write a book comparing these two pinnacles of social evolution [social insects and humans], but unfortunately one is obliged to wade through many pages of erroneous and downright perverse misunderstandings of evolutionary theory. In particular, Wilson now rejects “kin selection” (I shall explain this below) and replaces it with a revival of “group selection” – the poorly defined and incoherent view that evolution is driven by the differential survival of whole groups of organisms.
[…]
Then there’s the patrician hauteur with which Wilson ignores the very serious drubbing his Nature paper received. He doesn’t even mention those many critics: not a single, solitary sentence. Does he think his authority justifies going over the heads of experts and appealing directly to a popular audience, as if the professional controversy didn’t exist – as if acceptance of his (tiny) minority view were a done deal? “The beautiful theory [kin selection, see below] never worked well anyway, and now it has collapsed.” Yes it did and does work, and no it hasn’t collapsed. For Wilson not to acknowledge that he speaks for himself against the great majority of his professional colleagues is – it pains me to say this of a lifelong hero – an act of wanton arrogance.
[…]
“Inclusive fitness” was coined as a mathematical device to allow us to keep treating the individual organism (“vehicle”) as the level of agency, when we could equivalently have switched to the gene (“replicator”). You can say that natural selection maximises individual inclusive fitness, or that it maximises gene survival. The two are equivalent, by definition. On the face of it, gene survival is simpler to deal with, so why bother with individual inclusive fitness? Because the organism has the appearance of a purpose-driven agent in a way that the gene does not. Genes lack legs to pursue goals, sense organs to perceive the world, hands to manipulate it. Gene survival is what ultimately counts in natural selection, and the world becomes full of genes that are good at surviving. But they do it vicariously, by embryologically programming “phenotypes”: programming the development of individual bodies, their brains, limbs and sense organs, in such a way as to maximise their own survival. Genes programme the embryonic development of their vehicles, then ride inside them to share their fate and, if successful, get passed on to future generations.
So, “replicators” and “vehicles” constitute two meanings of “unit of natural selection.” Replicators are the units that survive (or fail to survive) through the generations. Vehicles are the agents that replicators programme as devices to help them survive. Genes are the primary replicators, organisms the obvious vehicles. But what about groups? As with organisms, they are certainly not replicators, but are they vehicles? If so, might we make a plausible case for “group selection”?
It is important not to confuse this question – as Wilson regrettably does – with the question of whether individuals benefit from living in groups. Of course they do. Penguins huddle for warmth. That’s not group selection: every individual benefits. Lionesses hunting in groups catch more and larger prey than a lone hunter could: enough to make it worthwhile for everyone. Again, every individual benefits: group welfare is strictly incidental. Birds in flocks and fish in schools achieve safety in numbers, and may also conserve energy by riding each other’s slipstreams – the same effect as racing cyclists sometimes exploit.
Such individual advantages in group living are important but they have nothing to do with group selection. Group selection would imply that a group does something equivalent to surviving or dying, something equivalent to reproducing itself, and that it has something you could call a group phenotype, such that genes might influence its development, and hence their own survival.
[…]
Edward Wilson has made important discoveries of his own. His place in history is assured, and so is Hamilton’s. Please do read Wilson’s earlier books […]. As for the book under review, the theoretical errors I have explained are important, pervasive, and integral to its thesis in a way that renders it impossible to recommend. To borrow from Dorothy Parker, this is not a book to be tossed lightly aside. It should be thrown with great force. And sincere regret.

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Ecco, Dawkins risponde negativamente alla mia seconda domanda (nell’ipotesi che il libro di Wilson sia affetto da errori teorici gravi, vale la pena egualmente di leggerlo?). Io sono però di diverso parere, e penso che invece possa essere letto fruttuosamente, anche se con qualche cautela.

Il breve capitolo 5, intitolato Threading the evolutionary maze, è un capolavoro di sintesi che riassume in 2 pagine l’origine dell’umanità da una prospettiva evoluzionistica.

E la metafora del labirinto evoluzionistico è un efficacissiomo esempio di intuition pump:

The possible evolution of a species can be visualized as a journey through a maze. As a major advance such as the origin of eusociality is approached, each genetic change, each turn in the maze either makes the attainment of that level less likely, or even impossible, or else keeps it open for access to the next turn. In the earliest steps that keep other options alive, there is still a long way to go, and the ultimate, far distant attainment is least probable. In the last few steps, there is only a short distance to go, and the attainment becomes more probable. The maze itself is subject to evolution along the way. Old corridors (ecological niches) may close, while new ones may open. The structure of the maze depends in part on who is traveling through it, including each of the species. [414]

Ma nel libro ci sono anche altri spunti profondi, che aprono vaste prospettive di riflessione. Ad esempio sulla divisione del lavoro, all’origine della crescita economica e del progresso:

Along with fireside campsites came division of labor. It was spring-loaded: an existing predisposition within groups to self-organize by dominance hierarchies already existed. There were in addition earlier differences between males and females and between young and old. Further, within each subgroup there existed variations in leadership ability, as well as in the proneness to remain at the campsite. The inevitable result emerging quickly out of all these preadaptations was a complex division of labor. [811]

O la riflessione che, l’acquisto di informazione ha un costo, la sua perdita è gratis:

For the neuroscientist, this explanation of an ethical decision by the would-be knifer has one very attractive feature: it involves only the loss of information, not its effortful acquisition or storage. The learning of complex information and its storage in memory are deliberate, painstaking processes, but the loss of information seems to take place with no trouble at all. Damping any one of the many mechanisms involved in memory can explain the blurring of identity required by this theory. [3981]

Ci sono poi le incursioni nei campi dell’economia …

Additional studies suggest (but have not yet conclusively proved) that leveling is beneficial even for the most advanced modern societies. Those that do best for their citizens in quality of life, from education and medical care to crime control and collective self-esteem, also have the lowest income differential between the wealthiest and poorest citizens. Among twenty-three of the world’s wealthiest countries and individual U.S. states, according to an analysis in 2009 by Richard Wilkinson and Kate Pickett, Japan, the Nordic countries, and the U.S. state of New Hampshire have both the narrowest wealth differential and the highest average quality of life. At the bottom are the United Kingdom, Portugal, and the remainder of the United States. [4037]

… della politica …

If personal benefit from group memberships rises high enough or, alternatively, if selfish leaders can bend the colony to serve their personal interests, the members will be prone to altruism and conformity. Because all normal members have at least the capacity to reproduce, there is an inherent and irremediable conflict in human societies between natural selection at the individual level and natural selection at the group level. [911]

… della religione …

The evidence that lies before us in great abundance points to organized religion as an expression of tribalism. Every religion teaches its adherents that they are a special fellowship and that their creation story, moral precepts, and privilege from divine power are superior to those claimed in other religions. […] The goal of religions is submission to the will and common good of the tribe. [4186-4192]

For outsiders openly to doubt such dogmas is regarded an invasion of privacy and a personal insult. For insiders to raise doubt is punishable heresy. [4197]

… della musica …

Patel has referred to music as a “transformative technology.” To the same degree as literacy and language itself, it has changed the way people see the world. Learning to play a musical instrument even alters the structure of the brain, from subcortical circuits that encode sound patterns to neural fibers that connect the two cerebral hemispheres and patterns of gray matter density in certain regions of the cerebral cortex. Music is powerful in its impact on human feeling and on the interpretation of events. It is extraordinarily complex in the neural circuits it employs, appearing to elicit emotion in at least six different brain mechanisms. [4583]

Ci sono poi alcune frasi fulminanti nella loro profondità:

[…] from diversity comes opportunity […] [480]

In a constantly changing world, we need the flexibility that only imperfection provides. [3887]

[…] prepared learning, the inborn propensity to learn something swiftly and decisively. [1009]

E infine, “semplici” esempi di divertito “bello scrivere”.

We have created a Star Wars civilization, with Stone Age emotions, medieval institutions, and godlike technology. [201]

Now, except for behaving like apes much of the time and suffering genetically limited life spans, we are godlike. [4639]

[…] the response of Samuel Foote to John Montagu, fourth Earl of Sandwich, when warned that he would die either by venereal disease or by the hangman’s noose. Foote responded, “My Lord, that will depend upon whether I embrace your lordship’s mistress or your lordship’s morals.” [4028]

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PS: mentre mi accingevo a esporre questo post sulla bacheca è sceso in campo (contro le tesi di Wilson e a favore della teoria dell’inclusive fitness) un altro pezzo da novanta, Steven Pinker. L’articolo è molto lingo e anche in questo caso vi invito ad andarlo a leggere per intero, su Edge: è stato pubblicato il 18 giugno 2012 ed è intitolato “The False Allure of Group Selection“.