▁name ▁appeared ▁in ▁print . ▁Dar win ▁made ▁a ▁presentation ▁of ▁both ▁discover ies ▁to ▁the ▁Pl in ian ▁Society ▁on ▁ 2 7 ▁March , ▁his ▁first ▁public ▁presentation . ▁Later ▁in ▁the ▁meeting ▁Brow ne ▁argued ▁that ▁mind ▁and ▁conscious ness ▁were ▁simply ▁aspects ▁of ▁brain ▁activity , ▁not ▁" s ou ls " ▁or ▁spiritual ▁entities ▁separate ▁from ▁the ▁body . ▁A ▁fur ious ▁debate ▁en su ed , ▁and ▁later ▁someone ▁deleted ▁all ▁mention ▁of ▁this ▁material ist ▁her es y ▁from ▁the ▁minutes . ▁This ▁was ▁Dar win ' s ▁first ▁expos ure ▁to ▁milit ant ▁fre eth ought ▁and ▁the ▁storm ▁it ▁stir red ▁up . ▁ ▁During ▁their ▁wal ks ▁Grant ▁exp ounded ▁his ▁ideas ▁to ▁Dar win , ▁and ▁on ▁one ▁occasion ▁dropped ▁his ▁guard ▁and ▁pra ised ▁L amar ck ' s ▁views ▁on ▁evolution . ▁He ▁explained ▁his ▁radical ▁theory ▁of ▁hom ology , ▁an ▁extension ▁of ▁the ▁idea ▁of ▁unity ▁of ▁plan ▁in ▁v og ue ▁in ▁Paris ▁at ▁the ▁time . ▁He ▁argued ▁that ▁all ▁animals ▁had ▁similar ▁org ans ▁differ ing ▁only ▁in ▁complexity ▁and , ▁controvers ial ly , ▁that ▁this ▁showed ▁their ▁common ▁descent . ▁Grant ▁had ▁announced ▁to ▁the ▁Werner ian ▁his ▁identification ▁of ▁the ▁pan cre as ▁in ▁a ▁p inned - out ▁sea - slug , ▁showing ▁an ▁organ ▁m oll us cs ▁shared ▁with ▁m amm als . ▁He ▁assumed ▁that ▁as ▁the ▁earth ▁co o led , ▁changing ▁conditions ▁drove ▁life ▁towards ▁higher