Human beings are capable, with little training, of memorizing long passages from literature.
Human beings are capable, with little training, to memorize long passages from literature.
Human beings are capable, with little training, of memorizing long passages from literature.
Human beings are capable, with little training, to memorize long passages from literature.
The adjective "capable" idiomatically takes "of + [gerund]," never an infinitive. Students sometimes confuse this idiom with the idiom for "able", which always takes an infinitive.