The authors explore the relationship between differences in technology adoption across cultures in snapshots from 1000 BCE, 0 CE, 1500 CE, and 2002 CE. While acknowledging various flaws inherent in the ambitious scope of their dataset, a significant relationship is nonetheless revealed between technology adoption in 1500 CE and technology and income in 2002 CE after controlling for various geographic and demographic factors. The authors suggest that this persistence may occur because technology adoption is heavily dependent on stock of prior technology.

The author investigates whether geographic factors--namely high elevation or 1500 m+ above sea level (reduced atmospheric pressure)-- impact the production, use, and ubiquity of ejective phonemes in eight non-contiguous language clusters. It is suggested that increased use of ejective phonemes has a physiological benefit: the reduction of water vapor loss via exhaled air. Evidence is presented in support of the hypothesized geographic-phonetic linkage.

The article examines whether cultural groups tend to use supernatural beliefs more to explain natural phenomena or social phenomena. Analysis of ethnographic text from 114 diverse societies reveals that supernatural explanations are more common for natural phenomena, consistent with the theory that humans tend to perceive intent and agency in the natural world. However, supernatural explanations of social phenomena were more prevalent in urbanized societies with greater social complexity and anonymity. The study highlights how people use supernatural beliefs to explain their world and how this varies across small-scale and urbanized communities.

This paper examines the relationship of productive variation in land between ethnic groups to determine if an increased range of producible goods will increase trade, thus decreasing language diversity between neighboring groups. The author initially found that high-variation in land production lessened the diversity of language between ethnic groups in that area. To further test this correlation, the author found that high-productive variation increased trade and exogamous marriage and decreased inter-ethnic conflict. Based on these findings, the author suggests that neighboring ethnic languages co-evolved through the economic benefit of inter-ethnic trade and social interaction.

The authors evaluated an alternative theory to the traditional productivity theory. They posit that food surplus did not precede the emergence of hierarchy, rather, the productivity advantage of cereal cultivation over tubers and roots as the catalyst for state societies. Their theory found support with a sample of societies from the present-day, Classical Antiquity, Neolithic period and pre/post Columbian Exchange. The results suggest social complexity emerged with cereal cultivation, rather than agriculture alone.

This paper "reduces Murdock's 210 categories to 30 variables, and intercorrelates and factor analyzes the variables for six world subdivisions as well as for the entire world." This article also discusses factor analysis as a method and examines the correlations more closely between the two regions that differed the most, North America and the Circum-Mediterranean.