The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


Costly courtship: the energetic burden of walking together

JANELLE M. WAGNILD and CARA M. WALL-SCHEFFLER.

Department of Biology, Seattle Pacific University

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Research has shown that individuals have an optimal walking speed–a speed which minimizes energy expenditure for a given distance. As the optimal walking speed varies with mass and lower limb length, it is therefore susceptible to sexually dimorphic variation, with males in any given population having faster optimal walking speeds; this potentially creates a dilemma for mixed-sex walking groups. Here we examine speed choices made by individuals of varying stature, mass, and sex walking together. Individuals (N=18) walked around a track alone, with a significant other (with and without holding hands), and with friends of the same and opposite sex while their speeds were recorded every 100m. Our findings show that males walk at a significantly slower pace to match the females’ paces (p=0.021), when the female is their romantic partner. Additionally, hand-holding causes both individuals to walk slower than either of their optimal speeds (for males significantly slower, p=0.016). Significant pace adjustment appears to be limited to romantic partners because the paces of friends of either sex walking together did not significantly change (p>0.05). These findings have implications for both mobility and reproductive strategies of groups. Because the male carries the energetic burden by adjusting his pace (slowing down 7%), the female is spared the potentially increased caloric cost required to walk together. In energetically demanding environments, we will expect to find mixed partner walking groups at a lower frequency than single sex groups particularly when travelling longer distances.

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