Your Evolved Intuitions

Part of the se­quence: Ra­tion­al­ity and Philosophy

We have already ex­am­ined one source of our in­tu­itions: at­tribute sub­sti­tu­tion heuris­tics. To­day we ex­am­ine a sec­ond source of our in­tu­itions: biolog­i­cal evolu­tion.

Evolu­tion­ary psychology

Evolu­tion­ary psy­chol­ogy1 has been cov­ered on Less Wrong many times be­fore, but let’s re­view any­way.

Lions walk on four legs and hunt for food. Skunks defend them­selves with a spray. Spi­ders make webs. Each species is shaped by se­lec­tion pres­sures, and is differ­ent from that of other species.

Cer­tain evolved psy­cholog­i­cal mechanisms in hu­mans are part of what makes us like each other and not like li­ons, skunks, and spi­ders.

Th­ese mechanisms evolved to solve spe­cific adap­tive prob­lems. It is not an ac­ci­dent that peo­ple around the world pre­fer calorie-rich foods,2 that women around the world pre­fer men with re­sources,3 that men around the world pre­fer women with signs of fer­til­ity,4 or that most of us in­her­ently fear snakes and spi­ders but not cars and elec­tri­cal out­lets.5

An an ex­am­ple of evolu­tion­ary psy­chol­ogy at work, con­sider the ‘hunter-gath­erer hy­poth­e­sis’ that men evolved psy­cholog­i­cal mechanisms to aid in hunt­ing, while women evolved psy­cholog­i­cal mechanisms to aid in gath­er­ing.6 This hy­poth­e­sis leads to a list of bold pre­dic­tions. If the hy­poth­e­sis is cor­rect, then:

  1. Men in mod­ern tribal so­cieties should spend a lot of time hunt­ing, and women more time gath­er­ing.

  2. Hu­mans should show a greater ten­dency to­ward strong male coal­i­tions than similar species in which males do not hunt much, be­cause strong male coal­i­tions are re­quired to hunt big game.

  3. Be­cause meat from most game comes in quan­tities larger than a sin­gle hunter can con­sume, and be­cause hunt­ing suc­cess is highly vari­able (one week may be a suc­cess, but per­haps not the next week), hu­mans should ex­hibit food shar­ing and re­cip­ro­cal al­tru­ism.

  4. We should ex­pect to see a sex­ual di­vi­sion of la­bor, due to the differ­ent traits con­ducive for hunt­ing vs. gath­er­ing.

  5. Men should ex­ploit sta­tus gains to be had from ‘show­ing off’ large hunt­ing suc­cesses.

  6. Men should have su­pe­rior cog­ni­tive abil­ity to nav­i­gate across large dis­tances and perform 3D men­tal ro­ta­tion tasks re­quired for throw­ing spears and similar hunt­ing acts. Women should have su­pe­rior cog­ni­tive abil­ity with spa­cial lo­ca­tion mem­ory and ob­ject ar­rays.

And as it turns out, all these pre­dic­tions are cor­rect.7 (And no, evolu­tion­ary psy­chol­o­gists do not only offer ‘post­dic­tions’ or ‘just so’ sto­ries. Be­sides, prob­a­bil­ity the­ory does not have sep­a­rate cat­e­gories for ‘pre­dic­tions’ and ‘post­dic­tions’.)

Kin loyalty

Con­sider the in­tu­ition that we have more re­spon­si­bil­ity for the well-be­ing of our close rel­a­tives than for the well-be­ing of dis­tant rel­a­tives or strangers. We would ex­pect hu­man evolu­tion to pro­duce ex­actly such an in­tu­ition given Hamil­ton’s rule, which states that the re­pro­duc­tive cost to an agent is less than the ge­netic re­lat­ed­ness of the re­cip­i­ent to the agent mul­ti­plied by the ad­di­tional re­pro­duc­tive benefit gained by the re­cip­i­ent of the al­tru­is­tic act.

That’s a mouth­ful, so in­stead let me illus­trate the con­se­quences of Hamil­ton’s rule:

Imag­ine that you pass by a river and no­tice that some of your ge­netic rel­a­tives are drown­ing in a fe­ro­cious cur­rent. You could jump in the wa­ter to save them, but you would pay with your own life. Ac­cord­ing to Hamil­ton’s rule, se­lec­tion will fa­vor de­ci­sion rules that, on av­er­age, re­sult in your jump­ing into the wa­ter to save three of your broth­ers, but not one. You would be pre­dicted not to sac­ri­fice your own life for just one brother, be­cause that would vi­o­late Hamil­ton’s rule. Us­ing the logic of Hamil­ton’s rule, evolved de­ci­sion rules should lead you to sac­ri­fice your own life for five nieces or nephews, but you would have to save nine first cous­ins be­fore you would sac­ri­fice your own life.8

Hamil­ton’s rule has in­deed been ob­served at work in a wide va­ri­ety of con­texts.9

My in­tu­ition that I am more re­spon­si­ble for the well-be­ing of my brother than my cousin, and more re­spon­si­ble for the well-be­ing of my cousin than a stranger, looks like a good can­di­date for an evolved in­tu­ition.


Une­d­u­cated peo­ple around the world be­lieve that or­ganisms come in dis­crete pack­ets, and that each species has an ‘essence’ that pro­duces its form and abil­ities. The in­tu­itive ap­peal of this es­sen­tial­ism of­ten trumps the ex­plic­itly learned grad­u­al­ism of biolog­i­cal evolu­tion. Even some­one who has read Richard Dawk­ins ar­gue against es­sen­tial­ism might find him­self the very next day stuck in es­sen­tial­ist think­ing. Why? Many re­searchers have sug­gested that an evolved, in­tu­itive ‘folk biol­ogy’ is re­spon­si­ble.10

Th­ese es­sen­tial­ist in­tu­itions emerge early in life across all cul­tures we have stud­ied.11 For ex­am­ple, chil­dren may be­lieve that

...if you re­move the in­sides of a dog, it loses its ‘essence’ and is no longer re­ally a dog any­more—it can’t bark or bite. But if you re­move its out­sides or change its ex­ter­nal ap­pear­ance so that it doesn’t look like a dog, chil­dren still be­lieve that it has re­tained its es­sen­tial ’dog­ness.’12

Many re­searchers think that es­sen­tial­ist in­tu­itions evolved be­cause it’s use­ful for hu­mans to re­spond to or­ganisms in this way. With es­sen­tial­ist think­ing, we can very quickly drop or­ganisms into cat­e­gories con­cern­ing what we can and can’t eat, what we can cap­ture, what might cap­ture us, and so on.

Essen­tial­ism has had a long-last­ing hold on the minds of many philoso­phers, and greatly in­fluenced their con­clu­sions even af­ter Dar­win.

Heuris­tics and biases

Hu­man rea­son­ing is sub­ject to a long list of bi­ases. Why did we evolve such faulty think­ing pro­cesses? Aren’t false be­liefs bad for sur­vival and re­pro­duc­tion?

Many re­searchers sug­gest that while hu­mans are poor at for­mal logic and Bayesian in­fer­ence, hu­mans dis­play a kind of ‘ecolog­i­cal ra­tio­nal­ity’.13

Over evolu­tion­ary time, the hu­man en­vi­ron­ment has had cer­tain statis­ti­cal reg­u­lar­i­ties: Rain of­ten fol­lowed thun­der, vi­o­lence some­times fol­lowed an­gry shouts, sex some­times fol­lowed pro­longed eye con­tact, dan­ger­ous bites of­ten fol­lowed get­ting too close to a snake, and so on. Th­ese statis­ti­cal reg­u­lar­i­ties are called ecolog­i­cal struc­ture. Ecolog­i­cal ra­tio­nal­ity con­sists of evolved mechanisms con­tain­ing de­sign fea­tures that uti­lize ecolog­i­cal struc­ture to fa­cil­i­tate adap­tive prob­lem solv­ing.

The shape and form of cog­ni­tive mechanisms, in other words, co­or­di­nate with the re­cur­ring statis­ti­cal reg­u­lar­i­ties of the an­ces­tral en­vi­ron­ments in which hu­mans evolved. We fear snakes and not elec­tri­cal out­lets...

[More­over], the­o­ries of for­mal logic that are con­tent in­de­pen­dent… are ex­cep­tion­ally poor at solv­ing real adap­tive prob­lems. The world is full of log­i­cally ar­bi­trary re­la­tion­ships: Dung hap­pens to be po­ten­tially dan­ger­ous to hu­mans, for ex­am­ple, but pro­vides a hos­pitable home for dung flies. So ap­ply­ing for­mal logic can­not in prin­ci­ple solve the adap­tive prob­lem of avoid­ing dung. The only thing that can solve it is a con­tent-spe­cific mechanism, one that has been built over evolu­tion­ary time to cap­i­tal­ize on the re­cur­ring statis­ti­cal reg­u­lar­i­ties as­so­ci­ated with dung as it in­ter­acted with our ho­minid an­ces­tors.14


Our brains may have evolved in­tu­ition-gen­er­at­ing mechanisms that worked for solv­ing par­tic­u­lar adap­tive prob­lems in the an­ces­tral en­vi­ron­ment, but we may not have evolved psy­cholog­i­cal mechanisms that gen­er­ate ac­cu­rate in­tu­itions use­ful for do­ing philos­o­phy. For ex­am­ple, it seems un­likely that we evolved a mechanism that gives us re­li­able in­tu­itions about the meta­phys­i­cal pos­si­bil­ity or im­pos­si­bil­ity of zom­bies.

Next post: In­tu­ition and Un­con­scious Learning

Pre­vi­ous post: How You Make Judgments


1 Re­cent in­tro­duc­tions to the field in­clude: Buss (2011); Work­man & Reader (2008); Gaulin & McBur­ney (2003). It is also worth men­tion­ing one of the ma­jor prob­lems with evolu­tion­ary psy­chol­ogy. Evolu­tion­ary psy­chol­o­gists tend to fo­cus on sub­jects that are difficult to test be­cause they are uniquely hu­man but also uni­ver­sally hu­man, which is bad for testa­bil­ity (see here and here). For other difficul­ties, see Prob­lems in Evolu­tion­ary Psy­chol­ogy.

2 Birch (1999); Krebs (2009).

3 Buss et al. (1990); Buss & Sch­mitt (1993); Khal­lad (2005); Gottschall et al. (2003); Gottschall et al. (2004); Ken­rick et al. (1990); Gus­tavs­son & Johns­son (2008); Wie­d­er­man (1993); Badah­dah & Tie­mann (2005); Mar­lowe (2004); Fis­man et al. (2006); Asendorpf et al. (2010); Bokek-Co­hen et al. (2007); Pet­tay et al. (2007).

4 Signs of fer­til­ity that men pre­fer in­clude youth (Buss 1989a; Ken­rick & Keefe 1992; Ken­rick et al. 1996), clear and smooth skin (Sugiyama 2005; Singh & Bron­stad 1997; Fink & Neave 2005; Fink et al. 2008; Ford & Beach 1951; Sy­mons 1995), fa­cial fem­i­ninity (Ganges­tad & Scheyd 2005; Schaefer et al. 2006; Rhodes 2006), long legs (Field­ing et al. 2008; Sorokowski & Pawlowski 2008; Ber­tam­ini & Ben­nett 2009; Swami et al. 2006), and a low waist-to-hip ra­tio (Singh 1993, 2000; Singh & Young 1995; Jasien­ska et al. 2004; Singh & Ran­dall 2007; Con­nolly et al 2000; Furn­ham et al 1997). Even men blind from birth pre­fer a low waist-to-hip ra­tio (Kar­re­mans et al. 2010). Note that stan­dards for beau­tiful faces emerge be­fore cul­tural can have much effect (Lan­glois et al. 1990) and that stan­dards of beauty are rel­a­tively con­sis­tent across cul­tures (Cun­ning­ham et al. 1995; Cross & Cross 1971; Jack­son 1992; Jones 1996; Thak­erar & Iwawaki 1979).

5 Buss (2011), pp. 92-94.

6 Buss (2011), p. 85.

7 Ev­i­dence cited by pre­dic­tion num­ber. 1: Hewlett (1991); Lee (1979). 2: Tooby & DeVore (1987). 3: Trivers (1971). 4: Roskraft et al. (2004); Tooby & DeVore (1987). 5: Hawkes (1991); Wiess­ner (2002). 6: Silver­man & Philips (1998); Silver­man et al. (2000); Eals & Silver­man (1994); Silver­man et al. (2007); New et al. (2007); Silver­man & Choi (2005); Lippa et al. (2010).

8 Buss (2011), p. 238-239.

9 Buss (2011) calls Hamil­ton’s the­ory of in­clu­sive fit­ness (ex­pressed in Hamil­ton’s rule) “the sin­gle most im­por­tant the­o­ret­i­cal re­vi­sion of Dar­win’s the­ory of nat­u­ral se­lec­tion in the past cen­tury” (p. 239). For a re­view of some of the ev­i­dence that sup­ports Hamil­ton’s rule, see Buss (2011), chap­ter 8.

10 Atran (1998); Ber­lin (1992); Keil (1995); Medin & Atran (1999).

11 Sper­ber & Hirschfeld (2004).

12 Buss (2011), p. 73.

13 Tooby & Cos­mides (1998). Hasel­ton et al. (2009) say hu­mans are ‘adap­tively bi­ased,’ while Ken­rick et al. (2009) say we are ‘adap­tively ra­tio­nal.’

14 Buss (2011), pp. 396-397.


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Atran (1998). Folk biol­ogy and the an­thro­pol­ogy of sci­ence: Cog­ni­tive uni­ver­sals and cul­tural par­tic­u­lars. Be­hav­ioral and Brain Sciences, 21: 547-609.

Badah­dah & Tie­mann (2005). Mate se­lec­tion crite­ria among Mus­lims liv­ing in Amer­ica. Evolu­tion and Hu­man Be­hav­ior, 26: 432-440.

Ber­lin (1992). Eth­no­biolog­i­cal clas­sifi­ca­tion. Prince­ton Univer­sity Press.

Ber­tam­ini & Ben­nett (2009). The effect of leg length on per­ceived at­trac­tive­ness of sim­plified stim­uli. Jour­nal of So­cial, Evolu­tion­ary, and Cul­tural Psy­chol­ogy, 3: 233-250.

Birch (1999). Devel­op­ment of food prefer­ences. An­nual Re­view of Nutri­cion, 19: 41-62.

Bokek-Co­hen, Peres, & Kanazawa (2007). Ra­tional choice and evolu­tion­ary psy­chol­ogy as ex­pla­na­tions for mate se­lec­tivity. Jour­nal of So­cial, Evolu­tion­ary, and Cul­tural Psy­chol­ogy, 2: 42-55.

Buss (1989). Sex differ­ences in hu­man mate prefer­ences: Evolu­tion­ary hy­pothe­ses test­ing in 37 cul­tures. Be­hav­ioral and Brain Sciences, 12: 1-49.

Buss (2011). Evolu­tion­ary Psy­chol­ogy: The New Science of Mind (4th ed.). Pren­tice Hall.

Buss & Sch­mitt (1993). Sex­ual strate­gies the­ory: An evolu­tion­ary per­spec­tive on hu­man mat­ing. Psy­cholog­i­cal Re­view, 100: 204-232.

Buss, Ab­bott, An­gleit­ner, Ash­e­rian, Bi­ag­gio, et al. (1990). In­ter­na­tional prefer­ences in se­lect­ing mates: A study of 37 cul­tures. Jour­nal of Cross-Cul­tural Psy­chol­ogy, 21: 5-47.

Con­nolly, Mealey, & Slaugh­ter (2000). The de­vel­op­ment of waist-to-hip ra­tio prefer­ences. Per­spec­tives in Hu­man Biol­ogy, 5: 19-29.

Cross & Cross (1971). Age, sex, race, and the per­cep­tion of fa­cial beauty. Devel­op­men­tal Psy­chol­ogy, 5: 433-439.

Cun­ning­ham, Roberts, Wu, Bar­bee, & Druen (1995). “Their ideas of beauty are, on the whole, the same as ours”: Con­sis­tency and vari­abil­ity in the cross-cul­tural per­cep­tion of fe­male at­trac­tive­ness. Jour­nal of Per­son­al­ity and So­cial Psy­chol­ogy, 68: 261-279.

Eals & Silver­man (1994). The hunter-gath­erer the­ory of spa­tial sex differ­ences: Prox­i­mate fac­tors me­di­at­ing the fe­male ad­van­tage in re­call of ob­ject ar­rays. Ethol­ogy and So­cio­biol­ogy, 15: 95-105.

Field­ing, Schol­ling, Adab, Cheng, Lao et al. (2008). Are longer legs as­so­ci­ated with en­hanced fer­til­ity in Chi­nese women? Evolu­tion and Hu­man Be­hav­ior, 29: 434-443.

Fink & Neave (2005). The biol­ogy of fa­cial beauty. In­ter­nal Jour­nal of Cos­metic Science, 27: 317-325.

Fink, Matts, Klin­gen­berg, Kuntze, Weege, & Gram­mar (2008). Vi­sual at­ten­tion to vari­a­tion in fe­male skin color dis­tri­bu­tion. Jour­nal of Cos­metic Der­ma­tol­ogy, 7: 155-161.

Fis­man, Iyen­gar, Ka­menica, & Si­mon­son (2006). Gen­der differ­ences in mate se­lec­tion: Ev­i­dence from a speed dat­ing ex­per­i­ment. The Quar­terly Jour­nal of Eco­nomics, 121: 673-697.

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Furn­ham, Tan, & McManus (1997). Waist-to-hip ra­tio and prefer­ences for body shape: A repli­ca­tion and ex­ten­sion. Per­son­al­ity and In­di­vi­d­ual Differ­ences, 22: 539-549.

Ganges­tad & Scheyd (2005). The evolu­tion of hu­man phys­i­cal at­trac­tive­ness. An­nual Re­view of An­thro­pol­ogy, 34: 523-548.

Gaulin & McBur­ney (2003). Evolu­tion­ary Psy­chol­ogy (2nd ed.) Pren­tice Hall.

Gottschall, Berkey, Caw­son, Drown, Fleischner, et al. (2003). Pat­terns of char­ac­ter­i­za­tion in folk­tales across ge­o­graphic re­gions and lev­els of cul­tural com­plex­ity: Liter­a­ture as a ne­glected source of quan­ti­ta­tive data. Hu­man Na­ture, 14: 365-382.

Gottschall, Martin, Quish, & Rea (2004). Sex differ­ences in mate choice crite­ria are re­flected in folk­tales from around the world and in his­tor­i­cal Euro­pean liter­a­ture. Evolu­tion and Hu­man Be­hav­ior, 25: 102-112.

Gus­tavs­son & Johns­son (2008). Mixed sup­port for sex­ual se­lec­tion the­o­ries of mate prefer­ences in the Swedish pop­u­la­tion. Evolu­tion­ary Psy­chol­ogy, 6: 454-470.

Hasel­ton , Bryant, Wilke, Fred­er­ick, Galperin, Fra­nen­huis, & Moore (2009). Adap­tive ra­tio­nal­ity: An evolu­tion­ary per­spec­tive on cog­ni­tive bias. So­cial Cog­ni­tion, 27: 733-763.

Hawkes (1991). Show­ing off: Tests of an­other hy­poth­e­sis about men’s for­ag­ing goals. Ethol­ogy and So­cio­biol­ogy, 11: 29-54.

Hewlett (1991). In­ti­mate Fathers: The na­ture and con­text of Aka pygmy pa­ter­nal in­fant care. Univer­sity of Michi­gan Press.

Jack­son (1992). Phys­i­cal ap­pear­ance and gen­der: So­cio­biolog­i­cal and so­cio­cul­tural per­spec­tives. State Univer­sity of New York Press.

Jasien­ska, Ziomk­iewicz, Elli­son, Lip­son, & Thune (2004). Large breasts and nar­row waists in­di­cate high re­pro­duc­tive po­ten­tial in women. Pro­ceed­ings of the Royal So­ciety of Lon­don, B, 271: 1213-1217.

Jones (1996). Phys­i­cal at­trac­tive­ness and the the­ory of sex­ual se­lec­tion. Univer­sity of Michi­gan Press.

Kar­re­mans, Franken­huis, & Arons (2010). Blind men pre­fer a low waist-to-hip ra­tio. Evolu­tion and Hu­man Be­hav­ior, 31: 182-186.

Keil (1995). The growth of un­der­stand­ings of nat­u­ral kinds. In Sper­ber, Premack, & Premack (eds.), Causal cog­ni­tion. Claren­don Press.

Ken­rick, Sadalla, Groth, & Trost (1990). Evolu­tion, traits, and the stages of hu­man courtship: Qual­ify­ing the parental in­vest­ment model. Jour­nal of Per­son­al­ity, 58: 97-116.

Ken­rick, Keefe, Gabrielidis, & Cor­nelius (1996). Ado­les­cents’ age prefer­ences for dat­ing part­ners: Sup­port for an evolu­tion­ary model of life-his­tory strate­gies. Child Devel­op­ment, 67: 1499-1511.

Ken­rick, Griske­vi­cius, Sundie, Li, Li, & Neu­berg (2009). Deep ra­tio­nal­ity: The evolu­tion­ary eco­nomics of de­ci­sion mak­ing. So­cial Cog­ni­tion, 27: 764-785.

Ken­rick & Keefe (1992). Age prefer­ences in mates re­flect sex differ­ences in re­pro­duc­tive strate­gies. Be­haivo­ral and Brain Sciences, 15: 75-133.

Khal­lad (2005). Mate se­lec­tion in Jor­dan: Effects of sex, so­cio-eco­nomic sta­tus, and cul­ture. Jour­nal of So­cial and Per­sonal Re­la­tion­ships, 22: 155-168.

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Lippa, Col­laer, & Peters (2010). Sex differ­ences in men­tal ro­ta­tion and line an­gle judg­ments are pos­i­tively as­so­ci­ated with gen­der equal­ity and eco­nomic de­vel­op­ment across 53 na­tions. Archives of Sex­ual Be­hav­ior, 39: 990-997.

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Singh (2000). Waist-to-hip ra­tio: An in­di­ca­tor of fe­male mate value. In­ter­na­tional Re­search Cen­ter for Ja­panese Stud­ies, In­ter­na­tional Sym­po­sium 16: 79-99.

Singh & Ran­dall (2007). Beauty is in the eye of the plas­tic sur­geon: Waist-to-hip ra­tio (WHR) and women’s at­trac­tive­ness. Per­son­al­ity and In­di­vi­d­ual Differ­ences, 43: 329-340.

Singh & Bron­stad (1997). Sex differ­ences in the anatom­i­cal lo­ca­tions of hu­man body scar­ifi­ca­tion and tat­too­ing as a func­tion of pathogen prevalence. Evolu­tion and Hu­man Be­hav­ior, 18: 403-416.

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