You can't let relativism interfere with the basic capacity to compare one group of people to another. The categories you pick and ways you talk about those categories influence the value of your observations. For example, it's easy to talk about the ways people are different but such observations are likely to place groups of people in different status positions. Religious differences, social classes, economic disparity.
Cultural comparison was very much on my mind during my recent trip to Peru. As a geographic place, the tourist region around the city of Cusco is a rich cultural environment. The history of multiple levels of cultural conflict plays out on a physically remarkable environment. While you're there it's perfectly appropriate to consider the history of the place.
The larger area of Peru and Equador was a culturally rich place in the Pre-Columbian era. Advanced civilizations were making anthropomorphic pottery and sophisticated human featured sculpture before Christ was born. The Incans were heirs to this broad, long running tradition in much the same way the Romans were heirs to the Greek/Mediterranean civilization.
The larger Peruvian civilization was handicapped because of a lack of writing. History mostly requires the presence of written language BEFORE events can be considered history. Thus, for civilizations without written language, you are looking at physical remains. Thus, the Incans are at the very cusp, with no written language tradition but physical remains that are top of the table. Most compelling for me is the symbol of the Incan Cross, pictured above at the Sun Temple in Pisaq. Wikipedia calls it the Chakana:
The Chakana (or Inca Cross, Chakana) symbolizes for Inca mythology what is known in other mythologies as the World Tree, Tree of Life and so on. The stepped cross is made up of an equal-armed cross indicating the cardinal points of the compass and a superimposed square. The square represents the other two levels of existence. The three levels of existence are Hana Pacha(the upper world inhabited by the superior gods), Kay Pacha, (the world of our everyday existence) and Ucu or Urin Pacha (the underworld inhabited by spirits of the dead, the ancestors, their overlords and various deities having close contact to the Earth plane). The hole through the centre of the cross is the Axis by means of which the shaman transits the cosmic vault to the other levels. It also represents Cuzco, the center of the Incan empire, and the Southern Cross constellation. (WIKIPEDIA)Pretty sophisticated concept, no writing required to explain it necessary. You come across that in a ruin at 10,000 feet up and you get it.