▁rock ▁groups ▁Category : Mus ical ▁groups ▁established ▁in ▁ 1 9 9 1 ▁Category : Mus ical ▁groups ▁dis est ab lished ▁in ▁ 1 9 9 5 ▁Category : Mus ical ▁quart ets ▁Category : Mus ical ▁groups ▁from ▁Kan ag awa ▁Pref ect ure ▁Category : 1 9 9 1 ▁establish ments ▁in ▁Japan <0x0A> </s> ▁Em otion ▁is ▁defined ▁as ▁any ▁mental ▁experience ▁with ▁high ▁intensity ▁and ▁high ▁h ed onic ▁content . ▁The ▁existence ▁and ▁nature ▁of ▁emot ions ▁in ▁animals ▁are ▁believed ▁to ▁be ▁correl ated ▁with ▁those ▁of ▁humans ▁and ▁to ▁have ▁evol ved ▁from ▁the ▁same ▁mechan isms . ▁Charles ▁Dar win ▁was ▁one ▁of ▁the ▁first ▁scient ists ▁to ▁write ▁about ▁the ▁subject , ▁and ▁his ▁observ ational ▁( and ▁sometimes ▁an ec dot al ) ▁approach ▁has ▁since ▁developed ▁into ▁a ▁more ▁robust , ▁hypothesis - dri ven , ▁scientific ▁approach . ▁C ogn itive ▁bias ▁tests ▁and ▁learned ▁hel pl ess ness ▁models ▁have ▁shown ▁feelings ▁of ▁optim ism ▁and ▁p ess im ism ▁in ▁a ▁wide ▁range ▁of ▁species , ▁including ▁r ats , ▁dogs , ▁c ats , ▁r hes us ▁mac a ques , ▁sheep , ▁ch icks , ▁star lings , ▁p igs , ▁and ▁h oney be es . ▁Ja ak ▁P ank se pp ▁played ▁a ▁large ▁role ▁in ▁the ▁study ▁of ▁animal ▁em otion , ▁bas ing ▁his ▁research ▁on ▁the ▁ne uro log ical ▁aspect . ▁M ention ing ▁seven ▁core ▁emot ional ▁feelings