Hu­mans are dif­fer­ent from other species, but not as much as we’ve as­sumed.

Hu­mans are dif­fer­ent from other species, but not as much as we’ve as­sumed.

New Zealand Listener - - CONTENTS - by Marc Wil­son

It makes you think” used to be a sales pitch for the Univer­sity of Welling­ton. I as­sume that is be­cause go­ing to univer­sity makes you think. I loved it, be­cause it lent it­self to so many vari­a­tions rel­e­vant to the mar­ket­ing of psy­chol­ogy. I still have my “Your brain – it makes you think” t-shirt. It’s a col­lec­tor’s item.

Brains are rub­bery things, and, prob­a­bly to gasps of my col­leagues who work more closely with them, I think it’s safe to say we’ve not got a com­plete han­dle on how they work.

Which isn’t to say we don’t know quite a lot. We know that dif­fer­ent bits are as­so­ci­ated with dif­fer­ent fac­ul­ties. For ex­am­ple, the amyg­dala, buried deep and just be­hind the eyes, is as­so­ci­ated with pro­cess­ing emo­tions. The pre­frontal cor­tex (PFC) is the bit up front and that’s im­por­tant for com­plex be­hav­iours like de­ci­sion-mak­ing.

We share a lot, but not all, of this gear with other species. Mon­keys also have amyg­dalas. Since at least the 1930s, we’ve known that mon­keys with­out amyg­dalas be­have quite dif­fer­ently from their in­tact peers. For in­stance, they don’t shy away from snakes and other dan­ger­ous an­i­mals. In­stead, they play with them. An­i­mals with­out amyg­dalas lose their sen­si­ble sense of fear.

The same thing ap­plies to us. One par­tic­u­larly rel­e­vant case is that of “SM” (brain folk give their cases ini­tials like this). SM has an un­usual con­di­tion that means she has no amyg­dala. If the amyg­dala is use­ful for gen­er­at­ing fear, and fear is a sign that there is dan­ger, it’s no sur­prise that SM finds her­self in trou­ble with­out re­al­is­ing it. In one ac­count, she would walk through the same park where she was mugged only the day be­fore.

For a long time, it’s been thought that not all an­i­mals have as ex­ten­sive frontal lobes as us. Ours are gen­er­ally large rel­a­tive to our to­tal brain vol­ume, but not our body size. Some lap dogs and fish do bet­ter on the lat­ter mea­sure than we do. Although it’s still gen­er­ally the case, there’s less rea­son for us to feel su­pe­rior to other species on the ba­sis of large frontal lobes alone – our PFCs are about as pro­por­tional to the size of other brain struc­tures as they are in other pri­mates.

For a long time, in our hubris, we also thought that we were the only species to ex­hibit cere­bral asym­me­try – two hemi­spheres of the brain that do dif­fer­ent things. The clas­sic ex­am­ple is lan­guage, the heavy lift­ing for which is done by one hemi­sphere or the other. For the ma­jor­ity of peo­ple, it is done by the left side of the ol’ burger.

An­other ex­am­ple is hand­ed­ness. The mus­cles on each side of our body are con­trolled by the op­po­site hemi­sphere, so a right-handed per­son is typ­i­cally left-hemi­sphere dom­i­nant. There is now abun­dant ev­i­dence of lat­er­al­i­sa­tion across a good num­ber of other an­i­mal species.

This brings me to bird brains. Many peo­ple would say that we should share more in com­mon with pri­mates than, say, the crow that ha­rasses my dog from the garage roof. But there’s some fas­ci­nat­ing re­search that shows that crows are also lat­er­alised.

Cale­do­nian crows dom­i­nate these dis­cus­sions be­cause they make and use tools to pry bugs out of crevices and they show a pref­er­ence for which side they hold and use their tools.

How­ever, crows and other species that show lat­er­al­i­sa­tion are typ­i­cally about 50:50 left or right dom­i­nant. So, rather than fo­cus­ing on how we’re spe­cially dif­fer­ent from other species, ques­tions tend to cen­tre on why we have a hemi­spheric dom­i­nance that re­sults in most of the pop­u­la­tion be­ing right-handed.

In one ac­count, “SM” would walk through the same park where she was mugged only the day be­fore.

Even split: A Cale­do­nian crow.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.