Behavioral science research in American universities was promoted and influenced by philanthropic foundations. In the 1920s and 1930s, Rockefeller philanthropies in particular financed behavioral science research projects that promised to fulfill their mandates to `improve mankind', mandates that foundation officers transformed into an informal, loosely defined human engineering effort. Controlling behavior, especially sexual and social `dysfunction', was a major priority. The behavioral scientists at Yale University, led by president James R. Angell and `psychobiologist' Robert M. Yerkes, tapped into foundation largesse (...) by crafting research programs that promised to contribute to the `welfare of mankind' through the investigation and control of sexual and social behavior. Foundation officers supported Yerkes' primate research because they accepted his premise that analyzing chimpanzee sexual behavior would yield valuable insights into the evolutionary underpinnings of human development and would thus give investigators the necessary information to ameliorate dysfunction. Between 1925 and 1940, philanthropic foundations contributed approximately $7 million to support the Yale Institute of Human Relations and the affiliated Yerkes Laboratories of Primate Biology. Yet, disappointment with the results of the Yale appropriations ultimately contributed to foundation officers turning away from behavioral sciences and toward biological sciences as they continued their efforts to improve mankind through human engineering. This article examines the interaction between foundation officers and Yale behavioral scientists to illustrate how scientific entrepreneurs successfully crafted rationales about human sexuality to solicit funds, how philanthropic foundation officers became enmeshed in the behavioral science research projects that they funded, and how a cooperative human engineering effort at Yale developed in the 1920s and unraveled in the 1930s. (shrink)