Differences between men's intellects?

Thesis 1: Men are equal in intellectual abilities (British Moral Philosophers)

Adam Smith (Wealth of Nations, book 1, Chap. 2)

The difference of natural talents in different men is, in reality, much less than we are aware of; and the very different genius which appears to distinguish men of different professions, 

when grown up to maturity, is not upon many occasions so much the cause as the effect of the division of labour. The difference between the most dissimilar characters, between a philosopher and a common street porter, for example, seems to arise not so much from nature as from habit, custom, and education. When they came into the world, and for the first six or eight years of their existence, they were, perhaps, very much alike, and neither their parents nor playfellows could perceive any remarkable difference. About that age, or soon after, they come to be employed in very different occupations. The difference of talents comes then to be taken notice of, and widens by degrees, till at last the vanity of the philosopher is willing to acknowledge scarce any resemblance... By nature a philosopher is not in genius and disposition half so different from a street porter, as a mastiff is from a greyhound, or a greyhound from a spaniel, or this last from a shepherd's dog.

David Hume (Of the Original Contract 1752)

...how nearly equal all men are in their bodily force, and even in their mental powers and faculties, till cultivated by education;

Thesis 2: Men are not equal in intellectual abilities (Enlightenment Philosophers)

John Locke (An Essay Concerning Human Understanding. book 4: chap 20, sec. 5)

affirm that there is a greater distance between some men and others in this respect than between some men and some beasts

Denis Diderot

He has not seen the insurmountable barrier that separates a man destined by nature for a given function, from a man who only brings to that function industry, interest and attention.