That is true, but it proves nothing.

Nature never forgot how to mould the head of Cicero or Livy.
She produces in every age men who might be great men; but the age does not always allow them to exert their talents.

Inundations of barbarians, universal wars, governments which discourage or do not favour science and art, prejudices which assume all variety of shapes--like the Chinese prejudice against dissecting corpses--may impose long periods of ignorance or bad taste.
But observe that, though the return to the study of the ancients revived, as at one stroke, the aesthetic ideals which they had created and the learning which they had accumulated, yet even if their works had not been preserved we should, though it would have cost us many long years of labour, have discovered for ourselves "ideas of the true and the beautiful." Where should we have found them?
Where the ancients themselves found them, after much groping.
6.
The comparison of the life of collective humanity to the life of a single man, which had been drawn by Bacon and Pascal, Saint Sorlin and Perrault, contains or illustrates an important truth which bears on the whole question.

Fontenelle puts it thus.

An educated mind is, as it were, composed of all the minds of preceding ages; we might say that a single mind was being educated throughout all history.