Why our brains weigh 1.3 kilograms, have ~100 billion neurons, consume 20% of the oxygen we breathe

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Team­work Builds Big Brains (Sci­ence Now):
— “The aver­age adult human’s brain weighs about 1.3 kilo­grams, has 100 bil­lion or so neu­rons, and sucks up 20% of the oxy­gen we breathe. It’s much big­ger than an ani­mal our size needs. Accord­ing to a new com­put­er mod­el, the brains of humans and relat­ed pri­mates are so large because we evolved to be social creatures.”
— “The idea behind the so-called social intel­li­gence hypoth­e­sis is that we need pret­ty com­plex com­put­ers in our skulls to keep track of all the com­plex rela­tion­ships we have with each other.”
— “… but points out that this hypoth­e­sis does­n’t explain all ani­mal brain­pow­er. New Cale­don­ian crows, for exam­ple, are impres­sive thinkers, but they aren’t social. He thinks that those birds have evolved intel­li­gence to deal with cer­tain hard-to-get foods. That need may also have con­tributed to the evo­lu­tion of intel­li­gence in apes, he says.”

Study: Coop­er­a­tion and the evo­lu­tion of intel­li­gence (Pro­ceed­ings of the Roy­al Society)

  • Abstract: The high lev­els of intel­li­gence seen in humans, oth­er pri­mates, cer­tain cetaceans and birds remain a major puz­zle for evo­lu­tion­ary biol­o­gists, anthro­pol­o­gists and psy­chol­o­gists. It has long been held that social inter­ac­tions pro­vide the selec­tion pres­sures nec­es­sary for the evo­lu­tion of advanced cog­ni­tive abil­i­ties (the ‘social intel­li­gence hypoth­e­sis’), and in recent years deci­sion-mak­ing in the con­text of coop­er­a­tive social inter­ac­tions has been con­jec­tured to be of par­tic­u­lar impor­tance. Here we use an arti­fi­cial neur­al net­work mod­el to show that selec­tion for effi­cient deci­sion-mak­ing in coop­er­a­tive dilem­mas can give rise to selec­tion pres­sures for greater cog­ni­tive abil­i­ties, and that intel­li­gent strate­gies can them­selves select for greater intel­li­gence, lead­ing to a Machi­avel­lian arms race. Our results pro­vide mech­a­nis­tic sup­port for the social intel­li­gence hypoth­e­sis, high­light the poten­tial impor­tance of coop­er­a­tive behav­iour in the evo­lu­tion of intel­li­gence and may help us to explain the dis­tri­b­u­tion of coop­er­a­tion with intel­li­gence across taxa.