Ifyourfatherwasleft-handedbutyourmotherwasright-handed, youhave a 17 percentchanceofbeingbornleft-handed, whiletworightieswillhave a left-handedchildonly 10 percentofthetime.
Andwhiletherehavebeenseveraltheoriesattemptingtoexplainwhyhandednessexistsinthefirstplace, orwhymostpeopleareright-handed, a recentmathematicalmodelsuggeststhattheactualratioreflects a balancebetweencompetitiveandcooperativepressuresonhumanevolution.
Ifpeoplewereonlyfightingandcompetingthroughouthumanevolution, naturalselectionwouldleadtomoreleftiesbeingtheonesthatmadeituntilthereweresomanyofthemthatitwasnolonger a rareasset.
Justasyoungpotentialgolferscanmoreeasilyfind a setofright-handedclubs, manyoftheimportantinstrumentsthathaveshapedsocietyweredesignedfortheright-handedmajority.
Sobycorrectlypredictingthedistributionofleft-handedpeopleinthegeneralpopulation, aswellasmatchingdatafromvarioussports, themodelindicatesthatthepersistenceofleftiesas a smallbutstableminorityreflectsanequilibriumthatcomesfromcompetitiveandcooperativeeffectsplayingoutsimultaneouslyovertime.