"Human beings naturally strive for understanding."
Pa/ntej a)/nqrwpoi tou= ei)de/nai o)re/gontai fu/sei.A question. Of course something like this idea is found, for instance, in Plato's account of eros. But is there a specific Platonic antecedent--some form of words in Plato upon which it might, with some plausibility, be said that Aristotle is building or drawing? I have only Ross' commentary on the Metaphysics to hand, and he refers simply to Jaeger's tracing the view to the Protrepticus.
I'll place suggestions here, since the Greek text may suitably be added.
Thomas Johansen has drawn attention to Timaeus 88a8-b2:
I would note Philebus 58d4:
dittw=n e)piqumiw=n ou)sw=n fu/sei kat' a)nqrw/pouj, dia\ sw=ma me\n trofh=j, dia\ de\ to\ qeio/taton tw=n e)n h(mi=n fronh/sewj"... since there are two desires natural to human beings, one for nourishment, attributable to the body, the other for wisdom, attributable the most divine element in us ..."
But it is the context of this remark that I find strikingly similar to Met. 1.1. Beginning by drawing a comparison with sight, Socrates argues that that there is a kind of knowledge which, although not useful, surpasses all the others in the clarity, accuracy, and truthfulness of its object (the superlative, a)lhqe/staton, is recurrent in the passage): thus, even a small portion of this is more valuable than any amount of useful knowledge. The passage, I think, quite mirrors the argument at the opening of the Metaphysics. But Socrates calls this knowledge phronesis; Aristotle, sophia.
... a)ll' ei)/ tij pe/fuke th=j yuxh=j h(mw=n du/namij e)ra=n te tou= a)lhqou=j kai\ pa/nta e(/neka tou/tou pra/ttein...."... but if some faculty of the soul naturally desires the truth and does everything for the sake of this..."