THE QUARTERLY REVIEW of Biology BORN TO THROW: THE ECOLOGICAL CAUSES THAT SHAPED THE EVOLUTION OF THROWING IN HUMANS Michael P. Lombardo Biology Department, Grand Valley State University Allendale, Michigan 49401-9403 USA e-mail: lombardm@gvsu.edu Robert O. Deaner Psychology Department, Grand Valley State University Allendale, Michigan 49401-9403 USA e-mail: robert.deaner@gmail.com keywords combat, fighting, human evolution, hunting, primates, throwing abstract Humans are the only species capable of powerful and accurate overhand throwing. However, the evolution of this ability remains underexplored. Here we draw on several lines of evidence—anatomical, archeological, cross-species comparisons, and ethnographic—to develop a scenario for the evolution of throwing. Throwing has deep roots in the primate lineage. Nonhuman primates throw projectiles during agonistic interactions but rarely to subdue prey. Thus, we argue that throwing first arose during ago- nistic interactions and was later incorporated into hunting by human ancestors. The fossil record in- dicates that anatomical adaptations for high-speed throwing in Homo first appeared about two million years ago. Once the effective use of projectile weapons became critical to success in combat and hunting, the importance of the ability to throw, intercept, and dodge projectiles would have resulted in stronger selection on males than females to become proficient at these skills because males throw projectiles more often than females in both combat and hunting. The Quarterly Review of Biology, March 2018 Vol. 93, No. 1 Copyright © 2018 by The University of Chicago Press. All rights reserved. 0033-5770/2018/9301-0001$15.00 Volume 93, No. 1 March 2018 1