It has been over 60 years since Ernst Mayr famously argued for the distinction between proximate and ultimate causes in biology. In the following decades, Mayr’s proximate-ultimate distinction was well received within evolutionary biology and widely regarded as a major contribution to the philosophy of biology. Despite its enormous influence, there has been a persistent controversy on the distinction. It has been argued that the distinction is untenable. In addition, there have been complaints about the pragmatic value of the distinction (...) in biological research. Some even suggest that the distinction should better be abandoned. In contrast, Mayr had consistently maintained the significance of the proximate-ultimate distinction in biology. There are also other attempts to defend the distinction. The paper examines the debate by taking an integrated History and Philosophy of Science (HPS) approach and argues for a functional approach to causal concepts in scientific practice. (shrink)