|Layne Vashro and wife Chelsea with Chief Koyo and family.|
This study conducted several tests of spatial ability on the subjects, including pointing to different directions in the Kunene region and stating whether a rotated hand on a screen was a left or a right hand after 7.5 seconds. It was found on the tests, after excluding individuals who didn't understand them, that men did significantly better than women. These findings, the research authors suggest, support the hypothesis that spatial ability has evolved in men for reproductive success. The reason for this, they continue, is because men who were better able to navigate long distances were also better able to find several mates with whom they could have children with; and since marriage does not restrict a man's sexual behaviours in these tribes, they were best to be studied, as they were less likely to be constrained by their marriages.
"Some people think it is culturally constructed, but that doesn't explain why the pattern is shared so broadly across human societies and even in some other species," explained Elizabeth Cashdan. At an initial glance, this seems like a pretty rational conviction with a cultural hypothesis: if this is contingent upon culture, then why is it that multiple cultures, and even multiple species, have these same abilities?
|The novel debate.|
Second of all, the hypothesis in question has little support from research which directly tests its viability. If spatial ability is a dimorphic trait which evolved in men over women to travel over wide ranges and navigate to find more mates and produce more offspring, then we should expect the differential to be constant across species with such wide ranges, and for the gap to decrease when ranges decrease. In fact, this is not the case. The comparative analysis by Clint et al. (2012) shows that across 35 studies of 11 species, while 8 out of 11 of the species do display this gap in spatial navigation, this tendency occurred regardless of the size of territories or the extent to which male ranges spanned further than female ranges. The authors suggest an alternative hypothesis, that perhaps the differential is a side effect of sex differences in testosterone, but there is little evidence to support this; certainly, however, there seems to not be much evidence, if any at all, for the evolutionary hypothesis.
Well, one reason which might suggest that spatial ability is the product of culture is that we know this to be the case based on already existing evidence; and in fact, the discrepancy between cultures (i.e. the lack of total universality) is what supports this.
To begin, consider the way direction is analyzed in the west; that is, in America, Canada, Europe, and so on -- English speaking countries. In common usage, direction is usually told respective to ourselves: left, right, front (or forward) and back (or behind). This is how we tell stories, how we give directions, and how we map the world around us, and in fact this has been fairly unproblematic in our daily lives. It's natural -- second nature to us, and because we can all understand it, we can all interact via these methods.
However, this method of navigation is not consistent between cultures. The most famous example of this is the Australian Aboriginal tribe, the Guugu Yimithirr. Their navigational abilities, unlike ours, are based on cardinal directions: North, South, East and West. Like us, this is also their practical use of direction, i.e. the one they use when speaking to other people, giving directions, telling stories, etc. When telling stories, for example, about when a fishing/hunting boat capsized, they would say the people jumped off the East side of the boat. When comparing the same story told by multiple individuals, this direction is remarkably consistent. This use of direction isn't biological, however, but is taught from a young age, as early as two.
|Guugu Yimithirr warriors.|
These are only two examples of how culture constructs our navigational abilities, and thus potentially explain the differences between cultures and even between sexes/genders in a particular culture. This analysis examines the differences between how cultures utilize direction without regarding gender. There is evidence, however, which examines the gender gap as well, and provides strong support for the cultural explanation, namely by displaying how difference in kinship and marriage systems might explain the discrepancy.
Consider the Khasi and Karbi tribes of northern India. The Karbi tribe practices a patrilineal kinship system, which (very briefly) means that inheritance and descent are passed down through men to their offspring. Characteristic of this type of kinship system is very strong, hard-to-break marriages as well as strict gender roles and restriction of women's sexuality. The Khasi tribe, on the other hand, is matrilineal, which means descent is passed down by women, by inheritance is passed by men -- but the assets which men own are often reliant on marrying women. Cultures which have this type of kinship system more often exhibit egalitarian characteristics, with women not being restricted in their sexuality, with relationships between siblings being strong, weaker marriages, etc.
|The Khasi people at a dancing festival in 2005.|
Admittedly, this doesn't explain why or how culture influences these factors, but lends very strong credence to the cultural hypothesis, and reconciles for factors which may not be accounted for by Vashro & Cashdan (2014). There are problems with the Hoffman study, however: their test of spatial abilities (an Object Assembly task) may or may not accurately represent the cognitive faculties in question. It should be noted however that their sample was a rare one, and was intended to promote future prospective research, but to my knowledge no such research has been conducted, likely due to the difficulties Hoffman et al. (2011) faced when attempting to teach their sample subjects how to conduct higher-level tasks of spatial abilities.
Nonetheless, this study remains significant for the subject at hand: whether or not Vashro & Cashdan's evolutionary hypothesis of sexually dimorphic expression for spatial cognition holds water. Likewise, the very fact that there exists such discrepancies in spatial abilities between cultures, and even within cultures, further supports the cultural hypothesis. Finally, while I won't discuss it in full detail here, we also have the pioneering work of anthropologist Dianna Shandy and economist Karine Moe to explain the cultural pressures which cause gender gaps in and different responses to certain tasks, including navigation.
It's honestly hard to believe that this recent research is being used to support the idea that spatial memory has evolved higher in men than women everywhere, even though there are clear cultural differences in this cognitive gap. To accept the evolutionary hypothesis, the trait should be much more universal than is the gap between genders in spatial abilities; nonetheless, this is a good example of western reductionism and how we find it very easy to find simple explanations for complex traits. This is much less a criticism of Vashro & Cashdan, but of the reports of their study. It's important to suggest alternatives in the scientific literature, as the two authors have done, but there are no definitive answers to be found here. We need to be careful that when we suggest an evolutionary explanation for observed traits, that the evidence is robust enough. While it's clear that there is cultural influence on spatial ability, there may be biological influences as well; however, the evidence at present, in my opinion, is not clear to support that suggestion.
Thank you all very much for reading.
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Haviland, J. (1998). Guugu Yimithirr Cardinal Directions. Ethos, 26 (1), 25-47 DOI: 10.1525/eth.1922.214.171.124
Hoffman, M., Gneezy, U., & List, J. (2011). Nurture affects gender differences in spatial abilities. Proceedings of the National Academy of Sciences, 108 (36), 14786-14788 DOI: 10.1073/pnas.1015182108
Vashro, L., & Cashdan, E. (2014). Spatial cognition, mobility, and reproductive success in northwestern Namibia. Evolution and Human Behavior, DOI: 10.1016/j.evolhumbehav.2014.09.009