A fundamental question in biology concerns the ways that species differ from one another.  Perhaps nowhere is this more prominent than in the field of biological anthropology, where many researchers investigate how and why humans differ from other primates, often under the assumption that human traits result from a unique constellation of forces that made our lineage particularly successful.  To rigorously identify the ways that humans differ from other primates requires data on the traits of interest, potential correlates of these traits, a phylogeny representing how the species in the analysis relate to one another, and an underlying evolutionary model of phenotypic trait change.  The research under this award made these methods available and applied them to rigorously investigate whether and how humans differ from other primates.

This research tested specific hypotheses for differences between humans and other primates through evolutionary analyses of a wide range of key variables involving brain size, a longer lifespan and related life history characteristics, sleep duration, and fundamental physiological variables, such as white blood cell counts and body temperature.  To achieve this goal, new statistical-evolutionary methods were developed to investigate whether human phenotypes differ from predictions based on comparative variation in primates.  The investigator also explicitly modeled trait covariation in primates under different evolutionary frameworks.  For some traits, these approaches were used to make inferences of when exceptional phenotypic changes occurred in human evolution.  

In addition to the methodological advances, the team made several important findings related to human evolution.  (1) The research revealed that humans sleep substantially less than predicted, and that this was achieved through reductions in non-rapid eye movement (NREM) sleep.  (2) Analyses quantified how much larger human brains are than expected based on variation in other primates, and also estimated the timing of brain size expansion in humans by applying these methods to endocranial volume on a hominin evolutionary tree (see figure).  (3) Analyses also demonstrated substantial deviations from predictions in some, but not all, life history traits in humans:  interbirth interval was shorter than predicted, longevity was longer than predicted, but age at first reproduction was not different from predicted based on phylogeny and cross-primate variation.  (4) We discovered that human physiology has shifted dramatically over the human lineage, with humans exhibiting more cases of exceptional phenotypic change than other species in the analysis. 

The research supported several important broader impacts, especially involving hands-on training in statistics and databases for the next generation of young scientists, and opportunities for these developing scientists to expand their knowledge of biology and anthropology.  Two of these trainees are now in top Ph.D. programs.  The research team also produced new methods to enable other scientists and students to investigate additional research questions important in the fields of biological anthropology.  The research has been presented at multiple scientific conferences – including by early-career scientists involved in the research – and at invited seminars by the Principal Investigator.

Last Modified: 05/01/2018
Modified by: Charles L Nunn