, ▁l ions , ▁t ig ers , ▁le op ards , ▁p um as ▁and ▁house ▁c ats ▁could ▁all ▁share ▁a ▁common ▁ancest or , ▁but ▁dogs ▁and ▁house ▁c ats ▁could ▁not . ▁ ▁Although ▁Dar win ' s ▁for ew ord ▁to ▁his ▁ 6 th ▁edition ▁of ▁Origin ▁cred ited ▁Arist ot le ▁with ▁for esh adow ing ▁the ▁concept ▁of ▁natural ▁selection , ▁he ▁also ▁wrote ▁that ▁" the ▁first ▁author ▁who ▁in ▁modern ▁times ▁has ▁treated ▁it ▁in ▁a ▁scientific ▁spirit ▁was ▁Buff on ". ▁ ▁Some ▁ 1 8 th - century ▁writers ▁spec ulated ▁about ▁human ▁evolution . ▁John ▁Mitchell , ▁a ▁phys ician ▁and ▁cart ograph er , ▁wrote ▁a ▁book ▁in ▁ 1 7 4 4 ▁called ▁An ▁Ess ay ▁upon ▁the ▁C aus es ▁of ▁the ▁D ifferent ▁Col ours ▁of ▁People ▁in ▁D ifferent ▁Cl im ates ▁in ▁which ▁he ▁claimed ▁that ▁the ▁first ▁race ▁on ▁earth ▁had ▁been ▁a ▁brown ▁and ▁re dd ish ▁colour ▁he ▁said ▁" that ▁an ▁intermediate ▁ta wn y ▁colour ▁found ▁amongst ▁A si at ics ▁and ▁Native ▁Amer ind ians " ▁had ▁been ▁the ▁“ original ▁complex ion ▁of ▁man kind ” ▁and ▁that ▁others ▁races ▁came ▁about ▁by ▁the ▁original ▁race ▁sp ending ▁gener ations ▁in ▁different ▁clim ates . ▁Between ▁ 1 7 6 7 ▁and ▁ 1 7 9 2 ▁James ▁Burn ett , ▁Lord ▁Mon b od do ▁included ▁in ▁his ▁writ ings ▁not ▁only ▁the ▁concept ▁that ▁man