Interracial marriage centuries before it was legal in the US.
Tens of universities.
And even a vaccine. Not a vaccine as we know them today but a vaccine nevertheless. [1]
To put it concisely, Europeans were deluded into the belief that hierarchy was ever-present - something which is heavily discredited historically. Further rationalizations that it must be so for a "developed, complex" society is evidently made spurious as well.
The various peoples of the Americas on the other hand, lacking in these diverse influences, and instead developing their own systems often altogether eschewed hierarchy and formalized coercive powers. Men and women in some cultures were very explicitly equal, and chiefs held little in the way of formal power. They were public speakers, and they had to present rational and convincing arguments - the rational tradition. This is a stark contrast to the feudal system and the heavy influence of the Roman Catholic church at the time. DoE suggests that certain figures had considerable influence on later though, providing citations from philosophers such as Montesquieu.
Their key argument comes from a highly-referenced individual named Kandiaronk, who is quite probably the basis for Adario in Baron Lahontan's books (evidently very popular), of particular interest:
"Finally, Supplement aux Voyages ou Dialogues avec le sauvage Adario lambasts institutional Christianity by means of a dialogue between de Lahontan and a Huron Chief named Adario (The Rat). The author attempts to contrast the injustice of Christianity with the freedom and justice of native people. His idealized view of "natural humanity" as a vehicle for criticizing European civilization was a forceful early expression of the "noble savage" trope associated with the Enlightenment."[1]
Evidently, Lahontan's writings were very popular:
"All these would be rather trivial concerns had Lahontan’s books not been so successful; but they were to have an enormous impact on European sensibilities. Kandiaronk’s opinions were translated into German, English, Dutch and Italian, and continued in print, in multiple editions, for over a century. Any self-respecting intellectual of the eighteenth century would have been almost certain to have read them." [2]
Coming from that point of reference, it wouldn't be surprising that Spain, having decades worth of exclusive exposure, would come out leading "liberal" thought. But is it fair to assert that it was Europeans that initiated it if it is so that they were inspired by the natives of the New World?
[1] https://en.wikipedia.org/wiki/Louis-Armand_de_Lom_d%27Arce_d... [2] Dawn of Everything