Does facial hair greying in chimpanzees provide a salient progressive cue of aging?

PLoS One. 2020 Jul 14;15(7):e0235610. doi: 10.1371/journal.pone.0235610. eCollection 2020.

Abstract

The greying of human head hair is arguably the most salient marker of human aging. In wild mammal populations, greying can change with life history or environmental factors (e.g., sexual maturity in silverback gorillas). Yet, whether humans are unique in our pattern of age-related hair depigmentation is unclear. We examined the relationship between pigmentation loss in facial hair (greying) to age, population, and sex in wild and captive chimpanzees (Pan troglodytes). Digital facial photographs representing three chimpanzee populations (N = 145; ages 1-60 years) were scored for hair greying on a scale of one [~100% pigmented] to six [~0% pigmented]. Our data suggest that chimpanzee head and facial hair generally greys with age prior to mid-life (~30 years old), but afterwards, greying ceases to increase incrementally. Our results highlight that chimpanzee pigmentation likely exhibits substantial variation between populations, and that both 'grey' and pigmented phenotypes exist across various age classes. Thus, chimpanzee facial hair greying is unlikely a progressive indicator of age beyond mid-life, and thus facial greying in chimpanzees seems different from the pattern observed in humans. Whether this reflects neutral differences in senescence, or potential differences in selection pressures (e.g. related to conspecific communication), is unclear and worthy of more detailed examination across populations and taxa.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aging / metabolism*
  • Animals
  • Biomarkers / metabolism
  • Female
  • Hair Color*
  • Male
  • Pan troglodytes*

Substances

  • Biomarkers

Associated data

  • Dryad/10.5061/dryad.f7m0cfxs7

Grants and funding

Funding for this study was from George Washington University, Yale University, and NSF (BCS-1546730). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.