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Was blackmail essential for marriage to evolve?

Dec. 2, 2011
World Science staff

The in­sti­tu­tion of mar­riage might not have suc­cess­fully taken root un­less black­mail was com­mon in an­cient hu­man so­ci­eties, a pro­voc­a­tive new study claims.

A tra­di­tion pub­licly and proudly dis­played in al­most eve­ry com­mun­ity, mar­riage is some­times sym­bol­ized by white trap­pings meant to con­vey that it is some­thing pure. But it may have largely been kept that way thanks to a dark en­force­ment mech­anism lurk­ing quite out of pub­lic view—and to the fear of it, according to the re­search­ers, who de­vel­oped math­e­mat­i­cal for­mu­las and com­put­er sim­ula­t­ions in sup­port of their the­o­ry.

The stu­dy, which at­tempts to de­scribe mar­i­tal rela­t­ion­ships with math­e­mat­ics as it might apply to a strat­e­gy game, is pub­lished in the Nov. 29 on­line is­sue of the re­search jour­nal BMC Ev­o­lu­tion­ary Bi­ol­o­gy

The re­search­ers with the In­di­an In­sti­tute of Sci­ence Educa­t­ion and Re­search in Pu­ne, In­dia and North Da­ko­ta State Uni­vers­ity in Far­go, N.D. said they set out to ex­plore the “co­nun­drum” of why males and fe­males sac­ri­fice their di­rect self-in­ter­est to get in­volved in mar­riage. 

Both males and fe­males can boost their in­di­vid­ual re­pro­duc­tive suc­cess through promiscu­ity. Yet the mar­riage in­sti­tu­tion has suc­ceeded in at least li­mi­ting un­ap­proved  rela­tion­ships, while con­fining many of those that re­main to the shad­ows of se­cre­cy.

While faithfully committed mar­riage is a good strat­e­gy for rais­ing chil­dren, that does­n’t ex­plain how it has re­mained sta­ble over time, added the re­search­ers, Milind Watve of the In­di­an In­sti­tute and col­leagues. They es­ti­mate that mo­nog­a­mous rela­t­ion­ships have been a fea­ture of hu­man mat­ing for mil­lions of years. As evi­dence they point out that hu­man males and fe­males have al­ways been fairly si­m­i­lar in size, a fac­tor as­so­ci­at­ed with lack of promiscu­ity across ma­ny spe­cies.

Part of the en­force­ment mech­a­nism that sup­ports mar­riage is “mate guard­ing,” they not­ed—the man and woman di­rectly mon­i­tor each oth­er and re­tal­i­ate for cheat­ing. A range of an­i­mals al­so prac­tice mate guard­ing. But the math sug­gests mate guard­ing is­n’t enough to en­force sta­ble mo­nog­a­my, Watve and col­leagues claim, es­pe­cially since this takes a sub­stantial in­vest­ment of en­er­gy from both par­ties.

In­stead, they ar­gue that at least among hu­ma­ns, “so­cial polic­ing” is al­so nec­es­sary. In plain Eng­lish, that’s the gos­sip fac­tor. Gos­sip helps ex­pose cheaters, who in ma­ny so­ci­eties suf­fer en­su­ing pun­ish­ments rang­ing from os­tra­cism to death. Gos­sip may al­so be more ef­fi­cient than mate guard­ing be­cause it’s eas­i­er: in place of sus­tained and fo­cused mon­i­toring of a per­son, oc­ca­sion­al, in­ci­den­tal ob­serva­t­ions may suf­fice.

But this begs the ques­tion, the re­search­ers note, of why peo­ple gos­sip, giv­en that this chat­ter al­so costs some time and ef­fort from eve­ryone in­volved. A glib an­swer might be that gos­sip is fun, but not eve­ryone finds it so, and our spe­cies as a whole might con­ceivably have evolved to find gos­sip un­bear­a­ble rath­er than en­joy­a­ble.

The cold real­ity is that the math works out only if eve­ry ac­tion has a pay­off or po­ten­tial pay­off, Watve and col­leagues ar­gue. In the case of gos­sip, they con­tend, that pay­off could have come in the form of black­mailing op­por­tun­i­ties. An ef­fec­tive gos­siper must al­so be a bus­y­body, and a bus­y­body gets ex­tra ac­cess to po­ten­tially dam­ag­ing se­crets that may oc­ca­sion­ally serve to ex­tract a hand­some pay­off from a hap­less cuck­old.

The mathematical mod­el de­vel­oped by Watve and col­leagues “indi­cates that ob­li­gate mo­nog­a­my is made pos­si­ble by black­mailing,” they wrote.

“We there­fore ar­gue that dur­ing the ev­o­lu­tion of mat­ing sys­tems, which is con­sid­ered as a main driv­ing force for the ev­o­lu­tion of [the] hu­man so­cial sys­tem, mo­nog­a­my was main­tained by so­cial polic­ing with op­por­tunis­tic black­mailing,” they added.

The real po­lice, of course, don’t like black­mailers much, some­thing all play­ers must take into ac­count. But for­mal polic­ing is a very re­cent phe­nom­e­non with lit­tle rel­e­vance to hu­man ev­o­lu­tion as it has played out over an es­ti­mated six mil­lion years. That’s the time since bio­logists say the lin­eages lead­ing to mod­ern hu­ma­ns and their clos­est liv­ing rel­a­tives, the chimps, be­came sep­a­rate.

“It can be spec­u­lat­ed that af­ter the ad­vent of a for­mal ju­di­ci­ary sys­tem, the pri­vate jus­tice of black­mailing could have been per­ceived as a threat to the for­mal ju­di­ci­ary sys­tem and there­fore con­sid­ered bad and il­le­gal,” Watve and col­leagues wrote. “How­ever, for­mal po­lice and ju­di­ci­ary sys­tems could nev­er re­place so­cial polic­ing through gos­siping and op­por­tunis­tic black­mailing both of which are prev­a­lent in mod­ern so­ci­eties too.”

One thing the mod­el does­n’t ex­plain is how mo­nog­a­my has aris­en some an­i­mal spe­cies, the re­search­ers ad­mit. It could be that among in non-hu­ma­ns mat­ings out­side the mo­nog­a­mous rela­t­ion­ship are more strongly lim­it­ed by short­age of op­por­tun­i­ties, they spec­u­lat­ed, but this re­mains to be seen.


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The institution of committed marriage might not have arisen unless blackmail was common in ancient societies, a provocative new study claims. Researchers developed mathematical formulas and computer simulations in support of the theory, which proposes that a tradition publicly and proudly paraded in almost every society—often symbolized by lily-white trappings—is buttressed at its core by a dark, hidden enforcement mechanism. The study, which attempts to describe marital relationships with mathematics as it might apply to a strategy game, is published in the Nov. 29 online issue of the research journal BMC Evolutionary Biology. The researchers with the Indian Institute of Science Education and Research in Pune, India and North Dakota State University in Fargo, N.D. said they set out to explore the “conundrum” of why males and females sacrifice their direct self-interest to get involved in marriage. Both males and females can boost their individual reproductive success through promiscuity. Yet the marriage institution has succeeded in at least partially stamping out extramarital matings, while generally limiting those illicit affairs that remain to the shadows of secrecy. While marriage is a good strategy for raising children, that doesn’t explain how it has remained stable over time, added the researchers, Milind Watve of the Indian Institute and colleagues. They estimate that monogamous relationships have been a feature of human mating for millions of years, since human males and females have always been fairly similar in size, a factor associated with lack of promiscuity across many species. Part of the enforcement machanism that supports marriage is “mate guarding,” they noted—the man and woman directly monitor each other and retaliate for cheating. A range of animals also practice mate guarding. But the math suggests mate guarding isn’t enough to enforce stable monogamy, Watve and colleagues claim, especially since this takes a substantial investment of energy from both parties. Instead, they argue that at least among humans, “social policing” is also necessary. In plain English, that’s the gossip factor. Gossip helps expose cheaters, who in many societies suffer ensuing punishments ranging from ostracism to death. Gossip may also be more efficient than mate guarding because it’s easier: in place of sustained and focused monitoring of a person, occasional, incidental observations may suffice. But this begs the question, the researchers note, of why people gossip, given that this chatter also some time and effort from everyone involved. A glib answer might be that gossip is fun, but not everyone finds it so, and our species as a whole might conceivably have evolved to find gossip unbearable rather than enjoyable. The cold reality is that the math works out only if every action has a payoff or potential payoff, Watve and colleagues argue. In the case of gossip, they contend, that payoff could have come in the form of blackmailing opportunities. An effective gossiper must also be a busybody, and a busybody gets extra access to potentially damaging secrets that may occasionally serve to extract a handsome payoff from a hapless cuckold. The model developed by Watve and colleagues “indicates that obligate monogamy is made possible by blackmailing,” they concluded. “We therefore argue that during the evolution of mating systems, which is considered as a main driving force for the evolution of [the] human social system, monogamy was maintained by social policing with opportunistic blackmailing,” they added. The police, of course, don’t like blackmailers much, and this can affect all players’ calculations. But formal policing is a very recent phenomenon with little relevance to human evolution as it has played out over an estimated six million years—the time since the lineages leading to modern humans and their closest living relatives, the chimps, became separate. “It can be speculated that after the advent of a formal judiciary system, the private justice of blackmailing could have been perceived as a threat to the formal judiciary system and therefore considered bad and illegal,” Watve and colleagues wrote. “However, formal police and judiciary systems could never replace social policing through gossiping and opportunistic blackmailing both of which are prevalent in modern societies too.” One thing the model doesn’t explain is how monogamy has arisen some animal species, the researchers admit. It could be that among in non-humans matings outside the monogamous relationship are more strongly limited by shortage of opportunities, they speculated, but this remains to be seen.