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Study may overturn thinking on human intellect

May 13, 2013
Courtesy of Durham University
and World Science staff

The su­pe­ri­or­ity of hu­man in­tel­li­gence is­n’t due mainly to the large size of the front part of our brain—con­trary to dec­ades of sci­en­tif­ic think­ing, say sci­en­tists.

New re­search con­cludes that this brain ar­ea, called the front­al lobes, is­n’t dis­pro­por­tion­ate­ly en­larged in hu­mans. So oth­er, sup­posedly more prim­i­tive brain ar­e­as may have been just as im­por­tant.

The lobes of the brain. New re­search con­cludes that the front­al lobes are not dis­pro­por­tion­ate­ly en­larged in hu­mans. (Im­age Cou­rtesy NIH)


“Hu­man front­al lobes are ex­actly the size ex­pected for a non-hu­man brain scaled up to hu­man size,” ex­plained Rob­ert Bar­ton of Dur­ham Uni­vers­ity in the U.K., lead au­thor of a re­port on the find­ings in this week’s early on­line is­sue of the jour­nal in the Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences.

The front­al lobes are a part of the brain of mam­mals lo­cat­ed at the front of each half, or hem­i­sphere, of the brain. 

Sci­en­tists had thought “it is our bulging front­al lobes that truly make us hu­man,” Bar­ton said. “Probably the most wide­spread as­sump­tion about how the hu­man brain evolved is that size in­crease was con­cen­trat­ed in the front­al lobes,” un­der­pin­ning mod­ern hu­man be­hav­ior, thought and lan­guage, he added.

The new find­ings mean “that ar­e­as tra­di­tion­ally con­sid­ered to be more prim­i­tive were just as im­por­tant dur­ing our evo­lu­tion,” he went on. “These oth­er ar­e­as should now get more at­ten­tion. In fact there is al­ready some ev­i­dence that dam­age to the cer­e­bel­lum, for ex­am­ple, is a fac­tor in dis­or­ders such as au­tism and dyslex­ia.”

Bar­ton and col­leagues ar­gue that many of our high-lev­el abil­i­ties de­pend on ex­ten­sive net­works link­ing many dif­fer­ent brain ar­e­as, so these net­works may be more rel­e­vant to cog­ni­tive func­tion­ing than the size of any iso­lat­ed re­gion.

Var­i­ous stud­ies have been done to see wheth­er hu­man front­al lobes are dis­pro­por­tion­ately large, but have re­sulted in a con­fused pic­ture with use of dif­fer­ent meth­ods and mea­sure­ments, the re­search­ers said. They an­a­lyzed da­ta sets from pre­vi­ous an­i­mal and hu­man stud­ies us­ing phy­lo­ge­net­ic, or “evo­lu­tion­ary family tree,” meth­ods, and found con­sist­ent re­sults across all their da­ta. They used a new meth­od to look at the speed with which ev­o­lu­tion­ary change oc­curred, con­clud­ing that the front­al lobes did­n’t change es­pe­cially fast along the hu­man twig of the family tree.


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The superiority of human intelligence isn’t due mainly to the large size of the front part of our brain—contrary to decades of scientific thinking, say scientists. New research concludes that this brain area, called the frontal lobes, isn’t disproportionately enlarged in humans, as previously thought. So other, supposedly more primitive brain areas may have been just as important. “Human frontal lobes are exactly the size expected for a non-human brain scaled up to human size,” explained Robert Barton of Durham University in the U.K., lead author of a report on the findings in this week’s early online issue of the journal in the Proceedings of the National Academy of Sciences. The frontal lobes are a part of the brain of mammals located at the front of each half, or hemisphere, of the brain. Scientists had thought “it is our bulging frontal lobes that truly make us human,” Barton said. “Probably the most widespread assumption about how the human brain evolved is that size increase was concentrated in the frontal lobes,” underpinning modern human behavior, thought and language, he added. The new findings mean “that areas traditionally considered to be more primitive were just as important during our evolution,” he went on. “These other areas should now get more attention. In fact there is already some evidence that damage to the cerebellum, for example, is a factor in disorders such as autism and dyslexia.” Barton and colleagues argue that many of our high-level abilities depend on extensive networks linking many different brain areas, so these networks may be more relevant to cognitive functioning than the size of any isolated region. Various studies have been done to see whether human frontal lobes are disproportionately enlarged, but have resulted in a confused picture with use of different methods and measurements, the researchers said. They analyzed data sets from previous animal and human studies using phylogenetic, or “evolutionary family tree,” methods, and found consistent results across all their data. They used a new method to look at the speed with which evolutionary change occurred, concluding that the frontal lobes didn’t change especially fast along the human twig of the family tree.