Disentangling the relationships between cultural traits and other variables

August 28, 2018

A team of researchers led by scientists at the Max Planck Institute for the Science of Human History and Australian National University analyzed how to avoid misinterpreting correlations in cross-cultural studies, published in Royal Society Open Science. The researchers identify three sources of non-independence in cultural variables - meaning, the variables are correlated but are not caused by each other - and present methods to control for these.

Recently, a growing number of researchers are hoping to gain insights into human cultural evolution and the diversity of human culture using comparative studies. In essence, this type of work looks for cultural traits or environmental factors that cause other cultural traits - such as the impact that subsistence strategy has on religious beliefs or the impact that the density of rivers has on language diversity. This work has been made vastly more approachable due to the expansion of large databases cataloging the relevant data, and the improvement of the programming and computing power necessary to make these comparisons. However, problems remain because many of the resulting studies make interpretations without controlling for factors that might make cultural variables seem causally related when they are not.

A team of researchers led by scientists at the Max Planck Institute for the Science of Human History and Australian National University has analyzed how to avoid misinterpreting correlations in cross-cultural studies and has identified three sources of non-independence in cultural variables - meaning, the variables are correlated, but are not caused by each other. The three sources identified are: (1) phylogenetic non-independence, meaning that the cultures are related to each other and a shared trait has been inherited by both from a common ancestor culture, rather than developed because it serves the same functional purpose in both cultures; (2) spatial autocorrelation, meaning the cultures share traits because they are geographically close to one another and thereby share many aspects of the same environment and history; and (3) covariation, meaning two traits correlate not because one causes the other but because both are caused or influenced by another variable.

The researchers then lay out guidelines to correct for these sources of non-independence and provide a case-study, looking at the connections between parasite load and various cultural and environmental factors. Parasite load has been hypothesized to have direct and dramatic impacts on a number of cultural traits - including religiosity, sexual behavior, in-group preference and population density. However, by controlling for the three sources of non-independence described above, the authors show that, contrary to previous studies, parasites have no more explanatory power for cultural traits than many other environmental factors like biodiversity, climate and latitude.

The authors emphasize that there are two issues at play with these sources of non-independence. One is whether two variables are correlated in the first place. Correcting for phylogenetic non-independence and spatial autocorrelation addresses this issue. The second is whether the correlation between two variables is evidence of a causal relationship. Correcting for covariation addresses this issue. This is important, because simply finding a correlation between two variables and then hypothesizing a possible causal mechanism between them is not enough to prove causality. "For example, people have hypothesized that the correlation between a high parasite load and lower average IQ is caused by the metabolic costs of infection reducing investment in cognitive development," explains Simon Greenhill of the Max Planck Institute for the Science of Human History. "However, this hypothesis is highly problematic as IQ also correlates just as strongly with other measures of biodiversity, such as number of mammal species. But we are not tempted to come up with a hypothesis to explain why having lots of mammal species reduces a nation's average IQ."

"Our results suggest that we must be cautious in interpreting these cross-cultural correlations as a reflection of causal connections," states Greenhill. "Correcting for statistical biases is necessary to avoid being led astray by interpreting incidental associations as meaningful of causal connections."
-end-


Max Planck Institute for the Science of Human History

Related History Articles from Brightsurf:

Reconstructing global climate through Earth's history
Accurate temperature estimates of ancient oceans are vital because they are the best tool for reconstructing global climate conditions in the past.

The colorful history of plastids
Emerging genome data provides new insight into plastid evolution.

The magnetic history of ice
The history of our planet has been written, among other things, in the periodic reversal of its magnetic poles.

Researchers map the evolutionary history of oaks
Oaks have a complex evolutionary history that has long eluded scientists.

Ancient Roman port history unveiled
A team of international researchers led by La Trobe University and the University of Melbourne have, for the first time worldwide, applied marine geology techniques at an ancient harbour archaeological site to uncover ancient harbour technologies of the first centuries AD.

The ancient history of Neandertals in Europe
Parts of the genomes of two ~120,000-year-old Neandertals from Germany and Belgium have been sequenced at the MPI for Evolutionary Anthropology.

A history of the Crusades, as told by crusaders' DNA
History can tell us a lot about the Crusades, the series of religious wars fought between 1095 and 1291, in which Christian invaders tried to claim the Near East.

The history of humanity in your face
The skull and teeth provide a rich library of changes that we can track over time, describing the history of evolution of our species.

Retrieving climate history from the ice
In the context of a major European Union project, experts from 14 institutions in ten European countries have spent three years combing the Antarctic ice, looking for the ideal site to investigate the climate history of the past 1.5 million years.

Rivers raged on Mars late into its history
A new study by University of Chicago scientists catalogued these rivers to conclude that significant river runoff persisted on Mars later into its history than previously thought.

Read More: History News and History Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.