If you want to be taken seriously, you need to cite something specific. "one of his books" covers over 10,000 pages of writing done over thirty years.
I can save you some trouble, however. I have researched a dozen claims made on FR that Darwin doubted his own theory. All such claims are rather easily proven to be lies. Not just incorrect interpretations, but deliberate and knowing lies, made by people with no scruples or conscience.
The standard method of writing by Darwin is to present the best case for his opposition and then repute it in detail. People who are entirely lacking in honesty will often pull a snippet from Darwin in which he is presenting his opponent's case -- then falsely impute the sentiment to Darwin.
All this demonstrates is that people who quote out of context are worshipping the Lord of Lies.