BSc Dissertation on hunter-gatherer theory available online

Copyright Gary and Glenn McCoy: http://www.gocomics.com/theflyingmccoys/2007/09/23

Copyright Gary and Glenn McCoy, 23/09/2007.

The first downloadable file have been put up. If you are interested in reading my BSc dissertation it is now available in the Download page.

The dissertation is about foraging-related stimuli and hunter-gatherer theory. It is somewhat based on a study by Krasnow et al. (2011), who found that on an absolute object location memory task (aOLM), women had a disadvantage with fruit stimuli. I was interested to see if this effect also occured in the conventional relative OLM task (in absolute OLM precision is involved, and no sex difference is usually observed. In relative OLM women tend to overall be better).

Research on foraging-related stimuli on OLM were scarce. Besides the Krasnow et al. (2011) study, the only other study to investigate this was Cashdan et al. (2012), who found no difference between fruit and animals on the task. They did not, however, compare results to controls.

We did an experiment were participants had to remember the location of objects and then subsequently place them where they had previously seen them. The stimuli was manipulated to include fruit, animals, and neutral stimuli. Hunter-gatherer theory (Silverman & Eals, 1992) suggested that women should generally be better at this task, so we predicted that women should outperform men in the neutral condition. Furthermore, as men were hunters their performance should improve with animal stimuli compared to neutral. Similarly, women should show improvement with fruit stimuli compared to neutral.

exp1_fruit2

The OLM task. Participants saw 6 items in a hexagonal orientation which they subsequently had to remember and place where they think they saw them.

Our results were mixed: Women were superior in the neutral condition, as expected. However, their advantage disappeared with BOTH fruit and animal stimuli. This only partially supports hunter-gatherer theory. It is, however, what Gathering-Navigation theory predicted (New, Krasnow et al., 2007; Kransow et al., 2011), as it suggests that fruit only benefit with women in absolute memory as it bears no advantage to remember a fruit location in relation to another fruit. This is something I regretably only realized retrospectively. The most likely explanation for our result is that fruit and animals are equally important from an evolutionary perspective to both sexes (men might hunt animals, but both sexes eat them or are aware of them / women might gather fruit, but both sexes eat them, and men might gather opportunistically while hunting). Most likely any impact stems from a much longer evolutionary history than hunter-gatherer theory suggests (e.g. rats also display OLM sex differences; Saucier et al., 2008).

As a follow-up experiment we did a reaction-time study to see if fruit and animal stimuli had any effect on perceptual search. It did not. There was no sex difference at all, suggesting fruit and animal stimuli has equal impact on both sexes. Any change in performance would be expected from both sexes using this stimuli. You might argue that perhaps it shows that fruit and animal stimuli have no effect at all and that the problem was with the neutral stimuli. Perhaps, but this is unlikely: previous research has shown that women are more likely to prefer colours associated with ripeness (Hulbert & Ling, 2007). People also tend to react equally fast to both plants and animals (Tipples et al., 2000), but are better at detecing movements in animals compared to non-organic objects like cars (New et al., 2007). Nevertheless, I think the mechanisms behind animal and fruit stimuli is not fully understood and more research is needed to investigate exactly why they have survival importance; otherwise we just end up with a just-so story.

The experiments were conducted at University of Essex together with Luke Cannon. Geoff Cole, PhD was the supervisor. If you are wondering what the mark was, it was 81%.

  • Cashdan, E., Marlowe, F.W., Crittenden, A., Porter, C., & Wood, B.M. (2012). Sex differences in spatial cognition among Hadza foragers. Evolution and Human Behaviour, 33, 4, 274-284.
  • Hulbert, A.C. & Ling, Y. (2007). Biological components of sex differences in color preference. Current Biology, 17, 16, 623-625.
  • Krasnow, M.M., Truxaw, D., Gaulin, S.J.C., New, J., Ozono, H., Uono, S., Ueno, T., & Minemoto, K. (2011). Cognitive adaptations for gathering-related navigation in humans. Evolution and Human Behavior, 32, 1-12.
  • New, J., Cosmides, L., & Tooby, J. (2007). Category-specific attention for animals reflect ancestral priorities, not expertise. Proceedings of the National Academy of Sciences, 104, 42, 16598-16603.
  • New, J., Krasnow, M., Truxaw, D., & Gaulin, S.J.C. (2007). Spatial adaptations for plant foraging: women excel and calories count. Proceedings of the Royal Society B, 274, 2679-2684.
  • Saucier, D.M., Shultz, S.R., Keller, A.J., Cook, C.M., & Binsted, G. (2008) Sex differences in object location memory and spatial navigation in Long-Evan rats. Animal Cognition, 11, 129-137.
  • Silverman, I. & Eals, M. (1992). Sex differences in spatial abilities: Evolutionary theory and data. In J.H. Barkows, L. Cosmides, & J. Tooby (Eds), The Adapted Mind: Evolutionary Psychology and the Generation of Culture (pp. 531-549). New York: Oxford Press.
  • Tipples, J., Young, A.W., Quinlan, P., Broks, P., & Ellis, A.W. (2002). Searching for threat. The Quarterly Journal of Experimental Psychology A: Human Experimental Psychology, 55, 3, 1007-1026.
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