▁caused ▁by ▁mut ations ▁improve ▁the ▁organ ism ' s ▁chance ▁of ▁surv ival . ▁Ada pt ive ▁mut ation ▁states ▁that ▁rather ▁than ▁mut ations ▁and ▁evolution ▁being ▁random , ▁they ▁are ▁in ▁response ▁to ▁specific ▁str esses . ▁In ▁other ▁words , ▁the ▁mut ations ▁that ▁occur ▁are ▁more ▁benef icial ▁and ▁specific ▁to ▁the ▁given ▁stress , ▁instead ▁of ▁random ▁and ▁not ▁a ▁response ▁to ▁anything ▁in ▁particular . ▁The ▁term ▁stress ▁refers ▁to ▁any ▁change ▁in ▁the ▁environment , ▁such ▁as ▁temperature , ▁nut ri ents , ▁population ▁size , ▁etc . ▁Test s ▁with ▁micro organ isms ▁have ▁found ▁that ▁for ▁adapt ive ▁mut ation , ▁more ▁of ▁the ▁mut ations ▁observed ▁after ▁a ▁given ▁stress ▁were ▁more ▁effective ▁at ▁dealing ▁with ▁the ▁stress ▁than ▁chance ▁alone ▁would ▁suggest ▁is ▁possible . ▁This ▁theory ▁of ▁adapt ive ▁mut ation ▁was ▁first ▁brought ▁to ▁academic ▁attention ▁in ▁the ▁ 1 9 8 0 s ▁by ▁John ▁C air ns . ▁ ▁Major ▁experiments ▁Ada pt ive ▁mut ation ▁is ▁a ▁very ▁controvers ial ▁topic ▁so ▁there ▁have ▁been ▁many ▁experiments ▁to ▁prove ▁or ▁dis cred it ▁the ▁theory . ▁Three ▁major ▁experiments ▁are ▁the ▁S OS ▁response ▁and ▁responses ▁to ▁star v ation ▁in ▁E scher ich ia ▁col i , ▁and ▁testing ▁for ▁revert ants ▁of ▁a ▁try pt oph an ▁aux ot roph ▁of ▁Sac char omy ces ▁c ere vis iae , ▁or ▁ye ast . ▁ ▁S OS ▁response ▁This ▁experiment ▁is ▁different ▁from ▁the