title: Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the 'challenge hypothesis'.
abstract: The challenge hypothesis posits that acute increases in testosterone (T) during male-male competition enhance performance and survivability while limiting the physiological costs of consistently high T. Human challenge hypothesis research focuses on young men in industrial populations, who have higher baseline T levels than men in subsistence populations. We tested whether the Tsimane, pathogenically stressed forager-horticulturalists of the Bolivian Amazon, would express acute T increases in response to physical competition. Saliva was collected from 88 Tsimane men (aged 16-59 years) before and after a competitive soccer match. Tsimane men had significantly lower baseline levels of T (β = -0.41, p < 0.001) when compared with age-matched United States (US) males. Linear mixed-effects models were used to establish that T increased significantly immediately following competition (β = 0.23, p < 0.001), remaining high 1 h later (β = 0.09, p = 0.007); equivalent to 30.1 and 15.5 per cent increases in T, respectively. We did not find larger increases in T among winners (p = 0.412), although T increases were positively associated with self-rated performance (β = 9.07, p = 0.004). These results suggest that despite lower levels of T than US males, Tsimane males exhibit acute increases in T at the same relative magnitude reported by studies in industrialized settings, with larger increases in T for those who report better individual performance.
authors.affiliation: Department of Anthropology, University of Washington, , Seattle, WA 98195, USA. ben.trumble@gmail.com
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Trumble
authors.forename: Daniel
authors.initials: D
authors.lastname: Cummings
authors.forename: Christopher
authors.initials: C
authors.lastname: von Rueden
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: O'Connor
authors.forename: Eric A
authors.initials: EA
authors.lastname: Smith
authors.forename: Michael
authors.initials: M
authors.lastname: Gurven
authors.forename: Hillard
authors.initials: H
authors.lastname: Kaplan
mesh_terms: D000293:Adolescent; D000328:Adult; D001838:Bolivia; D017753:Ecosystem; D006802:Human Activities; D006801:Humans; D007221:Industry; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012463:Saliva / Q000737:chemistry*; D012916:Soccer; D013312:Stress, Physiological; D013739:Testosterone / Q000737:chemistry* / Q000502:physiology*; D014481:United States; D055815:Young Adult
chemical_list: D013739:Testosterone