, ▁Pierre ▁Louis ▁Mau pert uis ▁ve ered ▁toward ▁more ▁material ist ▁ground . ▁He ▁wrote ▁of ▁natural ▁modifications ▁occurr ing ▁during ▁reprodu ction ▁and ▁accum ulating ▁over ▁the ▁course ▁of ▁many ▁gener ations , ▁producing ▁races ▁and ▁even ▁new ▁species . ▁He ▁also ▁anticip ated ▁in ▁general ▁terms ▁the ▁idea ▁of ▁natural ▁selection . ▁ ▁V ague ▁and ▁general ▁ideas ▁of ▁evolution ▁continued ▁to ▁pro l ifer ate ▁among ▁the ▁mid - e igh teenth ▁century ▁En light en ment ▁philosoph ers . ▁G . ▁L . ▁L . ▁Buff on ▁suggested ▁that ▁what ▁most ▁people ▁referred ▁to ▁as ▁species ▁were ▁really ▁just ▁well - mark ed ▁vari eties . ▁He ▁thought ▁that ▁the ▁members ▁of ▁what ▁was ▁then ▁called ▁a ▁genus ▁( which ▁in ▁terms ▁of ▁modern ▁scientific ▁classification ▁would ▁be ▁considered ▁a ▁family ) ▁are ▁all ▁desc ended ▁from ▁a ▁single , ▁common ▁ancest or . ▁The ▁ancest or ▁of ▁each ▁family ▁had ▁ar isen ▁through ▁sp ont aneous ▁generation ; ▁environmental ▁effects ▁then ▁caused ▁them ▁to ▁diver ge ▁into ▁different ▁species . ▁He ▁spec ulated ▁that ▁the ▁ 2 0 0 ▁or ▁so ▁species ▁of ▁m amm als ▁then ▁known ▁might ▁have ▁desc ended ▁from ▁as ▁few ▁as ▁ 3 8 ▁original ▁forms . ▁Buff on ' s ▁concept ▁of ▁evolution ▁was ▁strictly ▁limited . ▁He ▁believed ▁there ▁were ▁" internal ▁m olds " ▁that ▁sh aped ▁the ▁sp ont aneous ▁generation ▁of ▁each ▁family ▁and ▁that ▁the ▁families ▁themselves ▁were ▁entirely ▁and ▁et ern ally ▁distinct . ▁Thus