1. Sex differences in perception and memory of fruit and animal stimuli in relation to hunter-gatherer theory
Presented by Espen Sjoberg
University of Essex
Linked partner: Luke Cannon
Project supervisor: Geoff Cole

2. What is hunter-gather theory?
Proposed by Silverman & Eals (1992).
Attempts to explain sex differences in spatial abilities from an evolutionary perspective.
In Middle Pleistocene era (ca years ago), a labour division existed where men were hunters and women were gatherers, and from this different cognitive abilities have evolved.
Theory is post-hoc.

4. Men perform better than women on this task.
Mental rotation
Men perform better than women on this task.
Study of over participants across 40 countries yielded an effect size of 0.48 (Silverman, Choi, & Peters, 2007)
Object location memory
Women outperform men at this task.
Meta-analysis of 86 studies gave an effect size of 0.27 (Voyer, Postma, Brake & Imperato-McGinley, 2007).

5. Controversial evidence
Object-location memory
Female advantage disappears if items are moved to previously empty location rather than exchanged (James & Kimura, 1997)
Female advantage disappears when tested one week later (Honda & Nihei, 2009)
Female Long-Evan rats outperform males in object-location memory, despite absence of language and labour division (Saucier et al, 2008).

6. Our study
If men were hunters, then they would be more sensitive to animal stimuli, and all else being equal show an improvement in tasks with animal stimuli compared to other stimuli. Women would be more sensitive to fruit stimuli due to harvesting.

7. Our study
Looking at gender-specific sensitivity to hunter-gatherer related stimuli.
Based on Krasnow et al. (2011) who on an object location task found a female advantage with pictures of fruit on trees.
Experiment 1: Object-location task
Experiment 2: Reaction time experiment

8. Experiment 1
Object-location memory task 3 stimuli categories: Neutral, Animal, Fruit

11. Experiment 1 PREDICTIONS
Hunter-Gatherer Predicts:
Women better overall on this task
(even on animal stimuli men should not outperform women because
learning the present location of a mobile object is less useful for future
hunting (Krasnow et al., 2011))
Women better at neutral stimuli than men
Women better at fruit stimuli than neutral stimuli
Men better at animal stimuli than neutral stimuli

12. Experiment 1 RESULTS N = 76 p = .049 Correctly positioned pictures
Stimuli type

13. Experiment 2 Reaction-time experiment
Identify fruit or animal in 20-item array
Timed YES/NO responses

15. Experiment 2 PREDICTIONS
Hunter-Gatherer Predicts:
Women faster at fruit stimuli than animal stimuli
Men faster at animal stimuli than fruit stimuli

16. Experiment 2 RESULTS N = 53 p = .17, ns Reaction time (ms)
Stimuli type

17. Falsification issues
Hunter-gatherer theory is hard to falsify as evolutionary excuses can often explain unpredicted results.
Verbal memory and object location memory:
“The female advantage observed here may represent a rudimentary manifestation of superior verbal skills...If object and location memory are enhanced by verbal facilities in this manner, it may suggest that female verbal superiority at least its initial form, also evolved as part of division of labour”
(Silverman & Eals, 1992, p. 546)

18. Controversial evidence
Labour divisions
Kuhn & Stiner (2006)
The hunter-gatherer labour division most likely did not occur before Upper Paleolithic ( years ago)
Divisions of labour were plastic with individuals switching roles. Widows and daughters in families without sons would participate in hunting.

19. Final comment
The hunter-gatherer theory is becoming obsolete, but one of the main reasons it survives is because there is no viable opposing theory that can match it.

21. References:
Honda, A. & Nihei, Y. (2009). Sex differences in object location memory: the female advantage of immediate detection of changes. Learning and Individual Differences, 19,
James, T.W., & Kimura, D. (1997). Sex differences in remembering the locations of objects in an array: Location shifts, versus location-exchanges. Evolution and Human Behaviour, 18, 3,
Kuhn, S.L., & Stiner, M.C. (2006). What’s a mother to do? The division of labor among neandertals and modern humans in Eurasia. Current anthropology, 47, 6,
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,
Silverman, I., Choi, J., & Peters, M. (2007). The hunter-gatherer theory of sex differences in spatial abilities: Data from 40 countries. Archives of Sexual Behaviour, 36, 2,
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 ). New York: Oxford Press.
Silverman, I. & Eals, M. (1994) The hunter-gatherer theory of spatial sex differences.: Proximate factors mediating the female advantage in recall of object arrays. Ethology and Sociobiology, Vol .15, 2,
Voyer, D., Postma, A., Brake, B., & Imperato-McGinley, J. (2007). Gender differences in object location memory: A meta-analysis. Psychonomic Bulletin & Review, 14, 1, 23-38