Learning Outcomes. zAt the end of this session you should be able to: z1. Discuss the adaptive nature of spatial ability in animals and humans. z2. Discuss evolutionary explanations for sex differences in spatial ability.
Adaptive Significance of Spatial Ability. zEvolutionary theory predicts sexual dimorphism when males and females face different adaptive pressures. zVariation in hippocampal size (the seat of spatial processing) may be related to the degree of selection for spatial processing. zJacobs et al., (1990) argued that spatial ability should evolve in direct proportion to the navigational demands that an individual faces in everyday life. zWhilst males and females share the same environment, they may exploit their environment differently. In polygynous species males traverse large ranges to find mates, and such species should show greater sex differences in spatial ability than monogamous species.
Typical Range Sizes. Female Male Polygynous species Monogamous species From Gaulin, 1992 p 130,131.
Spatial Ability in Polygynous Versus Monogamous Voles. Polygynous Monogamous From Alcock, 1998, p 112
Hippocampal Size in Voles. zJacobs et al., (1990) compared hippocampal size in the polygynous meadow vole and the monogamous pine vole. zDuring the breeding season, adult males and females of each species were captured and the hippocampal area was determined. zIn the polygynous species male hippocampi averaged 11% larger than the female hippocampi, in the monogamous species this differences was only 2%. zThese differences were independent of body size. zHowever, a problem could be that males, having typically larger bodies and brains may thus happen to have larger hippocampi as a matter of course. zFurther evidence is required:
Range, and Hippocampal Sizes in Voles. Home range Hippocampal size From Sherry et al., 1992, p301
Evidence From Species Where Females Roam. zSherry et al., (1993) looked at hippocampal size in the parasitic brown-headed cowbird. zFemales search for host nests while males do not. zSpatial memory for the location of prime nests is a key requirement to successful egg laying. zThe authors did indeed find that the hippocampus was larger in cowbird females than males. zThere was no such difference in related but non-parasitic species, where males and females have similar spatial demands. This suggests it is spatial activity and not sex per se that influences relative hippocampal size.
Between-Species Comparisons. zSherry et al., (1992) looked at spatial memory and hippocampal size in food-storing and non food-storing birds. zFood-storers store single items of food in several hundred cache sites scattered throughout their home range during winter. zThey then revisit these sites on subsequent days by remembering the precise spatial location by learning geometric relationships among landmarks (Kamil & Jones, 1997). zThe authors reported that food-storers (black-capped chickadees, jays and nuthatches) had a hippocampus more than twice the size than that of non-storers. zThis was independent of sex.
Human Sex Differences in Spatial Ability. zVoyer et al., (1995) concluded that the largest male advantage was in tests of mental rotation, a moderate advantage in tests of spatial perception (e.g. rod and frame test) but no clear difference in spatial visualisation (e.g. embedded figures test). zMales are also better at spatial interception and throwing tasks (Halpern, 1992). zSuch differences are seen cross-culturally, and appear to have remained fairly stable over time. zThis indicates that while social factors may influence the expression of spatial skills, the sexes may be different before societal factors can have an influence. zThere are several evolutionary explanations for human sex differences in spatial abilities:
1. The Mating System Model. zGaulin (1992) proposed that cognitive mechanisms underpinning spatial ability are navigational adaptations. zIndividuals need to be able to find resources, to return to them, and to remember to avoid dangerous areas. zThis requires the ability to acquire, store, process, manipulate, and retrieve spatial information. zThe intensity of selection for such abilities should be proportionate to the magnitude of these demands. zSocial primates such as chimpanzees display sexually dimorphic ranging patterns with males travelling further than females as they patrol the boundary of their territory.
Human Ethnographic Evidence. zLike chimpanzees, it is generally accepted that humans are a species of polygynous ancestry with males searching out females, therefore natural selection would favour males who had superior spatial abilities. zMany ethnographers have noted that males travel more widely than females. zFor example, Hewlett et al., (1986) investigated travelling behaviours in the Aka Pygmies of central Africa. zMales had significantly larger exploration ranges. On the basis of the ‘Mating Systems Model’ we would predict that on various aspects of wayfinding and route learning, males should outperform females.
Wayfinding. zIt has been proposed that males and females may use different strategies to solve real-world spatial problems. zMales may use a geometrical strategy relying on the Euclidean properties of space (co-ordinates from angles, distances etc). zFemales may use topographical properties (the presence of and configural relations among landmarks). zFor example, McGuinness & Sparks (1983) noticed that when asked to draw maps of their campus, female students spontaneously drew more landmarks than did males.
Wayfinding Studies. zMiller & Santoni (1986): Presented males and females with schematic maps of a town consisting of streets with landmarks. They had to look at each map for 10min and then give precise directions from one part of the map to another. zThey then looked at the map for a further 5min and had to answer 10 questions concerning directions between various locations on the map. They found: Older participants were more accurate. Males were more accurate than females particularly on the maps with irregular street arrangements. Females were more likely to rely on landmark cues. Males were more likely to rely on geometrical cues.
Miller & Santoni (1986) Second Study. zThey used older participants, and made a note of which courses they had taken in high school or college. zThey also recorded the relative use of active versus passive transport. zThe same differences emerged in wayfinding knowledge with males outperforming females, and females relying more on landmark cues. zThey found positive correlations between: zAccuracy scores on this test and active transport. zAccuracy scores and type of courses studied. zMales had higher active travel scores and were much more likely to have taken courses such as geometry and trigonometry.
Galea & Kimura (1993). zMales and females learned a route through a novel map to criterion and then answered questions about the landmarks and the geometric properties of the map. zParticipants also received various cognitive tests. They found that: zMales performed significantly better on all measures of route learning. zFemales recalled and recognised more landmarks and street names. zMales better recalled the geometric properties of the map. zMales performed significantly better on the MRT. zMales and females did not appear to differ in their use of strategy to learn the route, both used a spatial strategy but males were more effective.
Other Studies. zLawton et al., (1996) led students on a circuitous route through hallways in a campus building and then asked to find their way back to a starting point. zThere were no sex differences on time to complete the task but males were more accurate on the direction task. zDabbs et al., (1998) asked 90 males and 104 females to complete cognitive spatial tests, give directions from a local map and identify places on a world map. zMales outperformed females at mental rotation, used Euclidean directional terms (such as 'East', 'West') while females gave more landmark information and males correctly identified more places on the world map.
Silverman et al., (2000). zLed participants along a 400m circuitous path through woodland with no visible landmarks. zDuring the walk, participants were asked to place an arrow pointing in the direction of where the walk began. zAt the end point participants were required to lead the experimenters back to the start point by the most direct route. Males performed better on both tasks. From Silverman et al., 2000, p206
2. The Division of Labour Model. zSilverman & Eals (1992) argued that the critical factor in selection for human spatial dimorphism was sexual division of labour between hunting and gathering during hominid evolution. zMales predominantly hunted whilst females predominantly gathered. zThey predicted that males should excel in cognitive abilities corresponding to hunting and navigational skills (mental rotations, map reading, maze learning, throwing). zFemales would excel in cognitive abilities involving the recognition and recall of objects (plants) within a spatial array
Silverman & Eals (1992) Study. zParticipants studied an array of familiar objects. zOn new sheets, they had to firstly identify new items, and then items that had moved. zFemales scored significantly higher on both tasks. Figures from Silverman & Eals, 1992 p537-538 Added items Moved items
Eals & Silverman (1994). zRepeated the experiment using uncommon objects. zIn an incidental version females were better at object recall, and significantly so at location memory. zIn a naturalistic setting a clear female advantage was again seen for location memory. Figures from Silverman & Eals, 1992 p98-99 Added itemsMoved items
Support for the ‘Gathering Hypothesis’. zMcBurney et al., (1997) used a gathering-analogue task based on the game ‘Memory’. zPlayers attempt to match pairs of objects depicted on cards that are arrayed face-down on the table. zPlayers can only turn 2 cards over in an attempt, and if they match, they are removed. zAs more cards are revealed then players can recall the locations of cards turned over previously. zThe authors argued that this game was a more ‘ecologically valid’ gathering task. zOn this task, females performed significantly better, while on the MRT males performed significantly better.
Female Advantage in Environmental Awareness? zMcGivern et al., (1998) assessed recognition memory in males and females using nameable objects, abstract shapes, and patterns in incidental and directed conditions. zParticipants were presented with a sheet of items, which they studied for 60s, the items were removed and they received a different sheet and asked to cross out all of the new items. zFemales recognised significantly more items than males in each category in both direct and indirect conditions. The authors argued that this reflects a female advantage in environmental awareness due in large part to nursing demands - i.e. having to be constantly vigilant with young children.
Male Hunting Prowess? zIf females are better at locating items within an array then are males better at hunting skills? zWatson & Kimura (1991) had male and female participants perform spatial interception (catching table-tennis balls fired in different directions from a launcher) and throwing with both hands (hitting a target 3m away using a throwing dart). zLarge sex differences favouring males were found on these dynamic spatial tasks using either hand. zThe authors suggested that such skills would have been vital for hunting and defence.
Wynn et al., (1996). zCriticised both 'Mating System' and 'Division of Labour ' models. zThey pointed that out that it is not yet understood exactly what cognitive processes are being used in the performance of different spatial tasks. zThey also argued that the largest spatial sex difference (mental rotation of 2D figures) exists on a test that has little relevance to everyday life. zFurthermore, ‘spatial perception’ which involves the ability to pick patterns out of complex backgrounds has some relevance (spotting a camouflaged animal) but does not show a large sex difference. But could this also be used to spot plants?
Lack of Archaeological Evidence. zWynn et al., (1996) also criticised the theories for their lack of confirming archaeological evidence. zFor example, males are supposed to better at certain spatiotemporal skills due to them developing superior throwing/aiming skills through hunting. zHowever, throwing projectiles appeared too late in human evolution to have had much influence on the development of these spatial abilities. zThey also argued out that both males and females would have engaged in foraging behaviours (much like chimpanzees) for the majority of human evolution, with males only engaging in correspondingly greater hunting activities much later.