Affiliations 

  • 1 Institute for Advanced Study in Toulouse, Toulouse, France vivekvasi@gmail.com
  • 2 Department of Human Evolutionary Biology, Harvard University, Cambridge, USA
  • 3 Department of Sociology, Philosophy and Anthropology, University of Exeter, Exeter, UK
  • 4 Department of Anthropology, University of California, Santa Barbara, Santa Barbara, USA
  • 5 Department of Anthropology, University of California, Santa Barbara, Santa Barbara, USA tkraft@anth.ucsb.edu
Proc Biol Sci, 2018 11 07;285(1890).
PMID: 30404871 DOI: 10.1098/rspb.2018.1492

Abstract

The convergent evolution of the human pygmy phenotype in tropical rainforests is widely assumed to reflect adaptation in response to the distinct ecological challenges of this habitat (e.g. high levels of heat and humidity, high pathogen load, low food availability, and dense forest structure), yet few precise adaptive benefits of this phenotype have been proposed. Here, we describe and test a biomechanical model of how the rainforest environment can alter gait kinematics such that short stature is advantageous in dense habitats. We hypothesized that environmental constraints on step length in rainforests alter walking mechanics such that taller individuals are expected to walk more slowly due to their inability to achieve preferred step lengths in the rainforest. We tested predictions from this model with experimental field data from two short-statured populations that regularly forage in the rainforest: the Batek of Peninsular Malaysia and the Tsimane of the Bolivian Amazon. In accordance with model expectations, we found stature-dependent constraints on step length in the rainforest and concomitant reductions in walking speed that are expected to compromise foraging efficiency. These results provide the first evidence that the human pygmy phenotype is beneficial in terms of locomotor performance and highlight the value of applying laboratory-derived biomechanical models to field settings for testing evolutionary hypotheses.

* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.