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Societies evolve a bit like creatures, study finds

Oct. 13, 2010
World Science staff

So­ci­eties evolve some­what simil­arly to the way liv­ing crea­tures do, in that in­creases in com­plex­ity tend to be grad­u­al, ac­cord­ing to new re­search pub­lished in the jour­nal Na­ture.

Most sci­en­tists “think that bi­o­log­i­cal ev­o­lu­tion hap­pens in in­cre­men­tal, small steps. We found the same thing in po­lit­i­cal ev­o­lu­tion,” said Cur­rie of Uni­vers­ity Col­lege Lon­don, U.K., one of the au­thors of the re­port in the Oct. 14 issue.

An ar­range­ment of lime­stone slabs on the is­land of Ton­gat­apu, Tonga in the Pa­cif­ic. It's thought to have been built as a gate­way to the roy­al com­pound of the 11th Par­a­mount Chief of Tonga at the be­gin­ning of the 13th cen­tu­ry. (Cred­it: Thom­as Cur­rie)

They de­fined po­lit­i­cal “com­plex­ity” as the num­ber of lay­ers of au­thor­ity, from lo­cal to re­gion­al pow­er bas­es cov­er­ing ever-ex­pand­ing ar­eas. In this pic­ture, the sim­plest so­ci­eties are small tribes or bands with one, of­ten in­for­mal, lead­er­ship role; the most com­plex are mod­ern na­tion-states, with mul­ti­ple lev­els of con­trol and bu­reauc­ra­cy. Many other socie­ties are some­where in be­tween.

Sci­en­tists have had trou­ble fully un­der­stand­ing how such com­plex­ity de­vel­ops, be­cause much of it oc­curred in pre­his­to­ry. The ar­chae­o­log­i­cal ev­i­dence is in­com­plete, and so­ci­e­tal or­gan­iz­a­tion is­n’t the kind of char­ac­ter­is­tic that tends to leave di­rect ev­i­dence in the ar­chae­o­log­i­cal rec­ord, Cur­rie not­ed.

Cur­rie and col­leagues sought to solve the prob­lem us­ing so-called phy­lo­ge­net­ic meth­ods, adapted from bi­ol­o­gy. In this approach, ex­ist­ing so­ci­eties are viewed as new branches of a family tree, much as cur­rently ex­ist­ing spe­cies are com­monly ar­ranged on an ev­o­lu­tion­ary or “fam­i­ly” tree. 

In ei­ther case, based on the mod­ern char­ac­ter­is­tics of these popula­t­ions, sci­en­tists try to re­con­struct how they probably looked when they first arose from com­mon pro­gen­i­tors, and what changes would have had to oc­cur since then.

In the case of or­gan­isms, sci­en­tists can use ge­net­ic da­ta to es­ti­mate when such com­mon an­ces­tors lived, since genes tend to change at a set rate. 

In the case of so­ci­eties, Cur­rie’s group used lan­guage in­stead of ge­net­ic da­ta. And they fo­cused on a spe­cif­ic family of so­ci­eties: speak­ers of Aus­tro­ne­sian lan­guages, com­mon through­out the Pa­cif­ic is­lands.

It’s a “par­tic­u­larly suit­a­ble da­tabase” of in­forma­t­ion, wrote Jar­ed Dia­mond of the Uni­vers­ity of Cal­i­for­nia, Los An­ge­les, in a sep­a­rate com­men­tary in the jour­nal. That’s be­cause the “lan­guage tree” for this group is very com­plete, he ob­served. More­o­ver, “ances­tral Aus­tro­ne­sian so­ci­eties un­der­went spec­tac­u­lar po­lit­i­cal dif­fer­entia­t­ion to give rise to ex­am­ples of the en­tire range of po­lit­i­cal or­gan­iz­a­tion, from small egal­i­tar­ian so­ci­eties such as Bor­neo’s Iban, through the sim­ple chief­doms of East­er Is­land and New Zea­land and the com­plex chief­doms of Ta­hi­ti and Su­ma­tra, to the Ja­van and Mal­a­gasy states.”

Cur­rie and col­leagues tested six com­pet­ing mod­els of po­lit­i­cal “ev­o­lu­tion” against the da­tabase and con­clud­ed that the best-fitting mod­el is one in which com­plex­ity in­creases or de­creases one step at a time—with one lay­er of au­thor­ity added or re­moved as a so­ci­e­ty in­creases or de­creases in com­plex­ity. 

A close sec­ond in terms of best-fitting mod­els, they added, was one in which com­plex­ity can in­crease only one step at a time, but can de­crease by more than one step at a time. This can oc­cur, for ex­am­ple, if a po­lit­i­cal sys­tem dis­in­te­grates or if a small group sets out to found a col­o­ny else­where.

One can make a “rough anal­o­gy” be­tween the path fol­lowed by so­cial ev­o­lu­tion and that fol­lowed by bi­o­log­i­cal ev­o­lu­tion, Cur­rie said—“sin­gle cells ag­gre­gat­ing in­to larg­er or­gan­isms, then groups of or­gan­isms.” More­o­ver, as in the ev­o­lu­tion of in­di­vid­ual spe­cies, com­pe­ti­tion plays an im­por­tant role in the shap­ing of so­ci­eties, and per­haps, their lev­els of com­plex­ity, Cur­rie and col­leagues wrote.

Re­gard­less of pre­cisely how this ev­o­lu­tion oc­curs, it seems “po­lit­i­cal ev­o­lu­tion is con­strained to fol­low only in­cre­men­tal in­creases in com­plex­ity,” the team wrote. “This could be due to such fac­tors as an evolved so­cial psy­chol­o­gy adapted to life in small-scale groups, the dif­fi­cul­ty in reor­ganizing ex­ist­ing in­sti­tu­tions that rely on the co­ordina­t­ion of large num­bers of in­di­vid­uals, or the re­quire­ment for the de­vel­op­ment of oth­er in­sti­tu­tions be­fore more hi­er­ar­chi­c or­gan­iz­a­tion is sta­ble.”

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Societies evolve somewhat the way organisms do, with increasing complexity usually arising gradually, according to new research published in the journal Nature. Most scientists “think that biological evolution happens in incremental, small steps. We found the same thing in political evolution,” said Currie of University College London, U.K., one of the authors. Currie and his group defined political “complexity” as the number of layers of authority, from local to regional power bases covering ever-expanding areas. In this picture, the simplest societies are small tribes or bands with one, often informal, leadership role; the most complex are exemplified by modern nation-states, with multiple levels of control and bureaucracy. Scientists have had trouble fully understanding how such complexity develops, because much of it occurred in prehistory. The archaeological evidence is incomplete, and societal organization isn’t the kind of characteristic that tends to leave direct evidence in the archaeological record, Currie noted. Currie and colleagues sought to solve the problem using “phylogenetic” methods borrowed from biology. In such a model, existing societies are viewed as new branches of a family tree, much as currently existing species are commonly arranged on an evolutionary or “family” tree. In either case, based on the modern characteristics of these populations, scientists try to reconstruct how they probably looked when they first arose from from common progenitors, and what changes would have had to occur since then. In the case of organisms, scientists can use genetic data to estimate when such common ancestors lived, since genes tend to change at a set rate. In the case of societies, Currie’s group used language instead of genetic data. And they focused on a specific family of societies: speakers of Austronesian languages, common throughout the Pacific islands. It’s a “particularly suitable database” of information, wrote Jared Diamond of the University of California, Los Angeles, in a separate commentary in the journal. That’s because the “language tree” for this group is very complete, he observed. Moreover, “ancestral Austronesian societies underwent spectacular political differentiation to give rise to examples of the entire range of political organization, from small egalitarian societies such as Borneo’s Iban, through the simple chiefdoms of Easter Island and New Zealand and the complex chiefdoms of Tahiti and Sumatra, to the Javan and Malagasy states.” Currie and colleagues tested six competing models of political “evolution” against the database and concluded that the best-fitting model is one in which complexity increases or decreases one step at a time—with one layer of authority added or removed as a society increases or decreases in complexity. A close second in terms of best-fitting models, they added, was one in which complexity can increase only one step at a time, but can decrease by more than one step at a time. This can occur, for example, if a political system disintegrates or if a small group sets out to found a colony elsewhere. One can make a “rough analogy” between the path followed by social evolution and that followed by biological evolution, Currie said— “single cells aggregating into larger organisms, then groups of organisms.” Moreover, as in the evolution of individual species, competition plays an important role in the shaping of societies, and perhaps, their levels of complexity, Currie and colleagues wrote. Regardless of precisely how this evolution occurs, it seems “political evolution is constrained to follow only incremental increases in complexity,” the team wrote. “This could be due to such factors as an evolved social psychology adapted to life in small-scale groups, the difficulty in reorganizing existing institutions that rely on the coordination of large numbers of individuals, or the requirement for the development of other institutions before more hierarchical organization is stable.”