Eileen Lacey is a behavioral ecologist whose research explores the ecological and 

evolutionary bases for variation in mammalian social behavior, with an emphasis on 

subterranean species of rodents. For the past three decades, she has used field and 

laboratory studies of tuco-tucos to try to understand why some members of this genus 

live in groups while others are solitary. This work has taken her to field sites from 

southern Peru to Tierra del Fuego to characterize the behavior of previously unstudied 

(and sometimes undescribed) species of tuco-tucos. It has also led her to explore the 

genetic, endocrine, and neuroendocrine correlates of differences in social relationships. 

Collectively, these efforts are revealing new insights into the adaptive bases for group 

living while underscoring the diversity and complexity of the factors shaping the social 

behavior of mammals.