 Wright's A Short History of Progress (2004) also argues for the primacy of environmental variables, but shifts the focus away from differential rates of development. Wright states that what is truly surprising is the similarity among developmental paths in areas isolated from one another (2004, 50).  In both Europe and the Americas, we see a movement from illiterate, egalitarian hunter-gatherer societies to complex and hierarchical agriculturally-based ones.  At the time of their confrontation, the worlds of the Spanish and the Aztecs were more alike than they were different.  Wright takes the similarity as strong evidence that universal environmental features and human needs drive development (51). 