aling ▁God ' s ▁underlying ▁plan ▁and ▁as ▁supporting ▁the ▁existing ▁social ▁hierarchy . ▁It ▁rejected ▁En light en ment ▁philosoph ers ▁such ▁as ▁David ▁H ume ▁who ▁had ▁argued ▁for ▁natural ism ▁and ▁against ▁belief ▁in ▁God . ▁ ▁The ▁discovery ▁of ▁foss ils ▁of ▁ext inct ▁species ▁was ▁explained ▁by ▁theories ▁such ▁as ▁cat ast roph ism . ▁Cat ast roph ism ▁claimed ▁that ▁animals ▁and ▁plants ▁were ▁period ically ▁anni h il ated ▁as ▁a ▁result ▁of ▁natural ▁cat ast roph es ▁and ▁then ▁replaced ▁by ▁new ▁species ▁created ▁ex ▁n ih ilo ▁( out ▁of ▁nothing ). ▁The ▁ext inct ▁organ isms ▁could ▁then ▁be ▁observed ▁in ▁the ▁foss il ▁record , ▁and ▁their ▁rep lac ements ▁were ▁considered ▁to ▁be ▁imm utable . ▁ ▁Dar win ' s ▁extended ▁family ▁of ▁Dar w ins ▁and ▁Wed g wood s ▁was ▁strongly ▁Un itar ian . ▁One ▁of ▁his ▁grand f athers , ▁Er as mus ▁Dar win , ▁was ▁a ▁successful ▁phys ician , ▁and ▁was ▁followed ▁in ▁this ▁by ▁his ▁sons ▁Charles ▁Dar win , ▁who ▁died ▁while ▁still ▁a ▁prom ising ▁medical ▁student ▁at ▁the ▁University ▁of ▁Edinburgh ▁in ▁ 1 7 7 8 , ▁and ▁Doctor ▁Robert ▁Dar win , ▁Dar win ' s ▁father , ▁who ▁named ▁his ▁son ▁after ▁his ▁dece ased ▁brother . ▁ ▁Er as mus ▁was ▁a ▁fre eth ink er ▁who ▁hypoth es ized ▁that ▁all ▁warm - blo oded ▁animals ▁spr ang ▁from ▁a ▁single ▁living ▁" fil