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Abstract ObjectiveReconstructing the social lives of extinct primates is possible only through an understanding of the interplay between morphology, sexual selection pressures, and social behavior in extant species. Somatic sexual dimorphism is an important variable in primate evolution, in part because of the clear relationship between the strength and mechanisms of sexual selection and the degree of dimorphism. Here, we examine body size dimorphism across ontogeny in male and female rhesus macaques to assess whether it is primarily achieved via bimaturism as predicted by a polygynandrous mating system, faster male growth indicating polygyny, or both. MethodsWe measured body mass in a cross‐sectional sample of 362 free‐ranging rhesus macaques from Cayo Santiago, Puerto Rico to investigate size dimorphism: (1) across the lifespan; and (2) as an outcome of sex‐specific growth strategies, including: (a) age of maturation; (b) growth rate; and (c) total growth duration, using regression models fit to sex‐specific developmental curves. ResultsSignificant body size dimorphism was observed by prime reproductive age with males 1.51 times the size of females. Larger male size resulted from a later age of maturation (males: 6.8–7.8 years vs. females: 5.5–6.5 years; logistic model) and elevated growth velocity through the pre‐prime period (LOESS model). Though males grew to larger sizes overall, females maintained adult size for longer before senescence (quadratic model). DiscussionThe ontogeny of size dimorphism in rhesus macaques is achieved by bimaturism and a faster male growth rate. Our results provide new data for understanding the development and complexities of primate dimorphism.
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Measurement and Assessment of Head-to-Helmet Contact Forces
Abstract PurposeTo evaluate the population variation in head-to-helmet contact forces in helmet users. MethodsFour different size Kevlar composite helmets were instrumented with contact pressure sensors and chinstrap tension meters. A total number of 89 volunteers (25 female and 64 male volunteers) participated in the study. The length, width, and circumference of their heads were measured and each volunteer was assigned a helmet size. Volunteers were asked to wear the helmet in three different configurations and the chinstrap tension and contact force between the head and each of the seven interior pads were recorded. ResultsThe majority of forces measured on any individual pad were between 0 and 5 N. However, some users exhibited pressure points with forces as high as 30 N. The contact force distribution is non-uniform across the interior of the helmet, with the largest force concentrated at the front. Head shape is a major driver of the observed contact force. There was a statistically significant difference between female and male volunteers, and between groups with different experience levels. ConclusionsThe fit of helmet systems is highly subject specific. The current metrics used to assign helmet sizes may not accurately predict correct helmet fit.
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- Award ID(s):
- 2049088
- PAR ID:
- 10568046
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Annals of Biomedical Engineering
- Volume:
- 53
- Issue:
- 4
- ISSN:
- 0090-6964
- Format(s):
- Medium: X Size: p. 946-955
- Size(s):
- p. 946-955
- Sponsoring Org:
- National Science Foundation
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