My copy of Descent has a different ordering of the phrasing, but the meaning is the same as what’s here:
Darwin, Charles. 1871. The Descent of Man. Chapter 5 - On the Development of the Intellectual and Moral Faculties During Primeval and Civilised Times
A paragraph and its notes:
Who can positively say why the Spanish nation, so dominant at one time, has been distanced in the race? The awakening of the nations of Europe from the dark ages is a still more perplexing problem. At that early period, as Mr. Galton has remarked, almost all the men of a gentle nature, those given to meditation or culture of the mind, had no refuge except in the bosom of a Church which demanded celibacy;* and this could hardly fail to have had a deteriorating influence on each successive generation. During this same period the Holy Inquisition selected with extreme care the freest and boldest men in order to burn or imprison them. In Spain alone some of the best men-- those who doubted and questioned, and without doubting there can be no progress-- were eliminated during three centuries at the rate of a thousand a year. The evil which the Catholic Church has thus effected is incalculable, though no doubt counterbalanced to a certain, perhaps to a large, extent in other ways; nevertheless, Europe has progressed at an unparalleled rate. * Hereditary Genius, 1870, pp. 357-359. The Rev. F. W. Farrar (_Fraser's Magazine_, Aug., 1870, p. 257) advances arguments on the other side. Sir C. Lyell had already (_Principles of Geology_, vol. ii., 1868, p. 489), in a striking passage, called attention to the evil influence of the Holy Inquisition in having, through selection, lowered the general standard of intelligence in Europe.