fei75766_ch16_495-533.indd 514  02/06/20 01:34 PM
Part VI    Learning-Cognitive Theories514
According toSkinner (1987a), human behavior (andhuman personality) is
shaped bythree forces: (1)natural selection, (2)cultural practices, and(3)theindi-
vidual’s history ofreinforcement, which wehavejustdiscussed. Inother words, Skin-
neracknowledged thatbehavior–environment interactions canchange behavior (and
even, thus, personality) inanindividual’s ownlifetimebutalsointhenatural or
cultural evolutionary history ofanentire group orspecies (Goddard, 2018).
Natural Selection
Human personality istheproduct ofalongevolutionary history. Asindividuals, our
behavior isdetermined bygenetic composition andespecially byourpersonal histo -
riesofreinforcement. Asaspecies, however, weareshaped bythecontingencies of
survival. Natural selection plays animportant partinhuman personality (Skinner, 
1974, 1987a, 1990a). 
Individual behavior thatisreinforcing tends toberepeated; thatwhich isnot
tends todropout.Similarly, those behaviors that,throughout history, werebenefi -
cialtothespecies tended tosurvive, whereas those thatwereonlyidiosyncratically 
reinforcing tended todropout.Forexample, natural selection hasfavored those indi-
viduals whose pupils oftheireyesdilated andcontracted withchanges inlighting. 
Their superior ability toseeduring bothdaylight andnighttime enabled them toavoid 
life-threatening dangers andtosurvive totheageofreproduction. Similarly, infants 
whose heads turned inthedirection ofagentle stroke onthecheek wereableto
suckle, thereby increasing theirchances ofsurvival andthelikelihood thatthisroot-
ingcharacteristic would bepassed ontotheiroffspring. These arebuttwoexamples 
ofseveral reflexes thatcharacterize thehuman infant today. Some, suchasthepupil -
laryreflex, continue tohavesurvival value, whereas others, liketherooting reflex, are
ofdiminishing benefit.
Thecontingencies ofreinforcement andthecontingencies ofsurvival interact, 
andsome behaviors thatareindividually reinforcing alsocontribute tothesurvival of
thespecies. Forexample, sexual behavior isgenerally reinforcing toanindividual, but
italsohasnatural selection value because those individuals whoweremost strongly 
aroused bysexual stimulation werealsotheonesmost likely toproduce offspring 
capable ofsimilar patterns ofbehavior.
Notevery remnant ofnatural selection continues tohavesurvival value. In
humans’ early history, overeating wasadaptive because itallowed people tosurvive 
during those times when foodwaslessplentiful. Now, insocieties where foodiscon-
tinuously available, obesity hasbecome ahealth problem, andovereating haslostits
survival value.
Although natural selection helped shape some human behavior, itisprobably 
responsible foronlyasmall number ofpeople’s actions. Skinner (1989a) claimed that
thecontingencies ofreinforcement, especially those thathaveshaped human culture, 
account formost ofhuman behavior.
Wecantrace asmall partofhuman behavior ...tonatural selection and
theevolution ofthespecies, butthegreater partofhuman behavior must be
traced tocontingencies ofreinforcement, especially totheverycomplex social 
contingencies wecallcultures. Only when wetakethose histories intoaccount 
canweexplain whypeople behave astheydo.(p.18)Final PDF to printer