In memoriam: Esther Thelen, May 20, 1941-December 29, 2004.

Dr. Esther (Stillman) Thelen, a prominent figure in the field of developmental psychology, died on December 29, 2004 after a yearlong battle with recurrent cancer. Professionally, Esther was known for her forward thinking, her elegant and prolific writing, her unapologetic embrace of the complexity of human behavior and its ultimate theoretical grounding in everyday life, and her tireless mentorship. During a career of less than 30 years, she rose to the pinnacle of her profession. She served as President of the Society for Research in Child Development and the International Society for Infant Studies. She was a Fellow of the American Association for the Advancement of Science and American Psychological Society. She received numerous grants from theNational Science Foundation and held continuous funding from the National Institutes of Health since 1987 including a Research Career Award, multiple Research Scientist Awards, and a Merit Award. She was on the editorial board of 17 journals including Developmental Psychobiology. Her work continues to influence researchers and clinicians in the fields of psychology, kinesiology, cognitive science, computer science, robotics, neuroscience, early childhood education, and pediatric rehabilitation. Esther was the intellectual mother to her students, post-docs, and collaborators, making sure all were nourished, cared for, and challenged. Esther loved traveling, opera, and entertaining friends and colleagues over fine food and wine at her home. Her love for life was without bounds (Fig. 1). Esther was born in Brooklyn, NY on May 20, 1941. She graduated from high school in Livingston, NJ, then attended Antioch College (Ohio) from 1959 to 1962 where she met her husband, David Thelen. She graduated from the University of Wisconsin in 1964 with a B.S. in Zoology. In 1973, she completed her M.A. in Zoology at the University of Missouri with a thesis on the grooming behavior of Bracon hebetor, a small parasitic wasp beneficial to the grain industry. During this project, she noted a conflict between the ‘‘fixed action patterns’’ she was supposed to find and the actual variability of the real life behavior of these animals. She recounted years later that this conflict suggested to her that individual variability and context appeared necessary for complex behaviors to emerge. Careful observations over multiple time scales and levels of organization, and the embrace of complexity were themes that would become her legacy. Interestingly, Esther was also becoming interested in Developmental Psychology and wondered if Piaget’s ‘‘circular reactions’’ were connected to the stereotypes in other animals.