Maurice O'Connor Drury in Conversations with Wittgenstein, ed. Rush Rhees (Oxford, 1984), pp. 160-161:
One day, walking in the Zoological Gardens, we admired the immense variety of flowers, shrubs, trees, and the similar multiplicity of birds, reptiles, animals.
Wittgenstein: I have always thought that Darwin was wrong: his theory does not account for all the variety of species. It hasn't the necessary multiplicity. Nowadays some people are fond of saying that at last evolution has produced a species that is able to understand the whole process which gave it birth. Now that you can't say.
Drury: You could say that now there has evolved a strange animal that collects other animals and puts them in gardens. But you can't bring the concepts of knowledge and understanding into this series. They are different categories entirely.
Wittgenstein: Yes, you could put it that way.Source: Maverick Philosopher