In 1837-1838 Charles Darwin drew in his notebook B a sketch of how evolution could take place. How one species can evolve into another one, and how different species are/can be related. This sketch embodies the evolutiontheory, one of the best documented theories in the scientific world.
It says:“Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction.
Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction. Thus genera would be formed. — bearing relation”
Yet, there is a small two-word text at the top of this page that is so exciting to me. He writes down: ‘I think’.
This little sentence shows that at that moment, C. Darwin was still in the phase of making his theory. But it also shows how science should be done and it shows his excellent scientific attitude i.e. always keep on doubting and searching.