Tuesday, June 9, 2015

Prisoners' Dilemma, Rock-Paper-Scissors and Human Sexual Evolution

 A series of prisoners dilemma games using my open source Mac application CA2D show varying success of the strategies on differing payoffs. (1-3) evolution under the default 3051;50;10;05. Defect black, tit-for-tat yellow, win-stay lose-shift red, random cooperate green, and cooperate blue. (4-5) 2050;25;10;05 results in hard defection followed by domination by tit-for-tat. (6) 4050;25;10;05 now has a mix of cooperate and win-stay lose-shift but if random is made more cooperative, it then becomes most populous.

Human sexual evolution is driven by mutual mate choice and particularly female reproductive choice, because of the vastly greater parenting investment and risk human females have to negotiate in a massive pregnancy, years of lactation and child rearing. Because we are at an extreme of mammals which bear live young, there is a large disparity between the reproductive strategies of men which emphasize fertilizing as many females as possible and women which emphasize securing resources and good genes (not necessarily from the same man) to support their huge parenting investment in a small number of offspring whose survival they need to ensure.

Thus human sexual selection is an outstanding example of the prisoners' dilemma (PD). Neither sex can do without the other, but each is tempted to defect to gain the upper hand in their own conflicting reproductive strategies. Evolutionary strategies in the PD vary from cooperation and defection to various mediating strategies - tit-for-tat do to an opponent what they did to you last time, win-stay - lose-shift, and other conditional strategies which invoke contextual cooperation and defection on a one-off basis, resulting in a dynamically evolving strategic ecosystem.

There is a nice face to this, in the form of the mating mind - the idea that female reproductive choice selects for smart men who are good providers, and resourceful hunters who love their womenfolk and have both the intelligence and prowess to protect them and their mutual offspring. At the same time mutual mate choice and the lusty throes of falling in love heal these conflicting agendas at least long enough for a couple, who are optimally unrelated so as to confer optimal disease resistance in their offspring, so share no direct genetic ties, can hold their parental relationship intact for the four to five years required to bring a child to the point of being able to cope in a complex human society.

On the other hand large brained intelligent primates from capuchins to humans depend on strategic bluffing to mediate complex social responses enabling complex societies with many niches to exist. The Machiavellian intelligence theory posits that intelligence is centrally about social astuteness and judging good character, in a broadly cooperative milieu, albeit with subterranean deception to take advantage of naive participants where exploitation has easy advantages and few costs, and frank and often lethal defection when the stakes are high and opposing forces enter the stark choices of high noon. But strategic bluff is all about deception and consequently the green eyed anathema of sexual deceit branded the ultimate betrayal, because of its primary threat to male paternity certainty when it is a woman and the potential loss of long term familial support when it is a man. This is where rock-paper-scissors (RPS) comes into the picture.

Diverse Rock-Paper-Scissors dynamics using my open-source Mac application CA2D: Lower centre, 01010100 r generates two classes of demons the narrow ones dominant over the disordered milieu and the wider ones developing from flaws in the former recessive to both. The seed states generating these demons cannot come into being once the dynamic has reached cyclic evolution. Left: Contrast between partial demons of 01111100 r (below) and the cycling regions expanding until one reaches overall dominance of inverse rule 01101100 r (above) with fine-scale cyclic stratification illustrate the differing strategies of cycle-forward-on-lose and cycle-backward-on-lose. Top center: 01211100 r shows larger regions of cycic dominance. It has been noted that counterintuitively moving to the next weaker state on losing can be a winning strategy in the real game. Right: 01111090 x2 shows the effects of 10% mutation facilitating regions of local dominance as well as evolving cyclic fluctuations of the overall population between the three states under iteration.

One can see the female strategies spread between scarlet whores who deny men any reproductive certainty, but offer unconstrained pleasure in return thus defecting against male reproduction, and on the other hand faithful wives, cooperators who a man can hopefully be sure of, but who may be demanding, and jealous of the man's ability to take advantage of other sexual opportunities, just as men can become lethally jealous of women because of innate paternity uncertainty. Men can live with either of these strategies but the third clandestine one they fear like the plague and torture with all manner of grievous punishments, from female genital mutilation, to stoning for adultery, is the deception strategy of females, who seek a stable man to resource their family only to have affairs on the side, siring the odd child with a physically superior man they are sexually attracted to. Thus deception enters the female strategy repertoire to form an RPS triad.

In turn male strategies are also divided into a rock-paper-scissors triad. Faithful husbands who invest in the fidelity of their partner by following the tenets of social monogamy. The trouble here is that social monogamy is just what it says 'social' not reproductive. This truth is common to colonial birds like albatrosses and to prairie voles both of which have life-long relationships but clandestine reproductive trysts on the side.  On the other hand, men are notorious at spreading wild oats with an insatiable lust barely containable by the assets of a stable family life. A man who is dashing and has charisma and superior genetic vigor can afford to wander from town to town as a minstrel or soldier of fortune and score a maiden in every place he lays his head. At the other extreme the lords of the manner can demand first rights to every newly wed in the shire and potentates from Tamerlane on down reputedly had ten thousand virgins behind flaming walls. But deception is also a primary and highly successful strategy for men who seek social mobility and positions from which to have an affair with their secretary, a kept woman in a discrete apartment, or simply a quick shag at a rave where the mood is unhinged.

 The Rock-Paper-Scissors like three-way Prisoners' Dilemma game matrix illustrates three strategies each for woman and men. In a population of faithful wives a rare scarlet woman can have all she asks for. Conversely, a faithful wife is a prized asset in a society of loose women. This rareness factor prevents the annihilation of either strategy.

The principal thrust of patriarchy is to repress female reproductive choice, which is both pivotal to XY-based sex chromosome evolution and which is essential for women because of the huge parenting investment and danger of human pregnancy lactation and child-rearing and the much smaller number of offspring a woman can nurture by comparison with a powerful or popular male. Invocations against adultery are primarily targeted at women as the 'devils gateway' along with dire punishments such as stoning. Men are happy to exploit both the defecting scarlet women and the faithful wives,but the idea of a female who looks like a faithful wife doing it on the sly with the brawny bloke down at the pub is an anathema to male paternity certainty.

The strategy of deception arises naturally as a function of the strategic bluffing which is the hallmark of the Machaivellian intelligence that enables the complex social niches of lage brained species from capuchins to humans. Virtually all social concourse and the tests of good character revolve around detecting subtle social signals indicating whether a person can be trusted in a climate of charisma and spin. Machiavellian intelligence complements the genuine indicators of fitness involved in the sexual complementation of courtship - the "mating mind" - of good husbanding and astute reproductive choice based on sexual love. Strategic bluffing is a form of strategic deception designed to increase the exsting payoffs from a broadly cooperative milieu by taking advantage of easily deceived participants of low cast. The end result is that deceit plays a central role as a third option in all human societies despite being demonized as the purveyor of betrayal.

It is easy to see how deception is a key player in both men and women for differing reasons, temptation to form an external liaison can enter into a committed relationship partly whenever it is perceived as an additional bonus with little chance of detection. As existing relationships become a burden it is also easy to see how deception can also give way to outright defection, when a man finds his wild oats investments are more suited to his power and sexual charisma than an existing chain around his neck. In turn outright defection can destroy a man's chance of reproductive success when the local community discovers down the grape vine that he is an untrustworthy  psychopath.  We thus effectively end up with a complex sexual dynamic of prisoners' dilemma strategies between the conflicting reproductive investments of the two sexes amid a rock-paper-scissors cyclic dominance in each sex's strategic milieu.

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