Спаси Бог за информацию, очень не приятно читать и использовать фразы, вырванные из контекста. Пришлось найти первоисточник.
http://www.gutenberg.org/files/2009/2009-h/2009-h.htm
Можно только обратить внимание на перевод: Дарвин использовал не " препятствующие принять", а "to be very great in believing”, что скорее звучало ближе к "верить" (в крайнем случае к "предполагать").

"When we reflect on these facts, here given much too briefly, with respect to the wide, diversified, and graduated range of structure in the eyes of the lower animals; and when we bear in mind how small the number of all living forms must be in comparison with those which have become extinct, the difficulty ceases to be very great in believing that natural selection may have converted the simple apparatus of an optic nerve, coated with pigment and invested by transparent membrane, into an optical instrument as perfect as is possessed by any member of the Articulata class."