 Candolle originated the idea of " Nature 's war " , which influenced Charles Darwin and the principle of natural selection. de Candolle recognized that multiple species may develop similar characteristics that did not appear in a common evolutionary ancestor ; this was later termed analogy . During his work with plants , de Candolle noticed that plant leaf movements follow a near @-@ 24 @-@ hour cycle in constant light , suggesting that an internal biological clock exists . Though many scientists doubted de Candolle 's findings , experiments over a century later demonstrated that ″ the internal biological clock ″ indeed exists . 
