Despite the proliferation of research on public service motivation (PSM), fundamental questions about its origins continue to evade scholars: Is PSM driven by genetics, socialized through experiences, or both? If PSM is socialized, when does socialization occur? Answering these questions is critical for reconciling the state versus trait debate, and for assessing the validity of practical implications prescribed by PSM studies. Utilizing “nature's own experiment,” we adopt a classical twin design with 1035 twin pairs to identify how genetic heritability, a common environment, or unique environment and experiences can explain variation in PSM. Results show that PSM is heavily influenced by individuals' unique environments and experiences; not by genetics. This lends strong evidence to PSM's uniqueness as a motivational construct as related “other-regarding” concepts show sizeable genetic components. Finally, our results corroborate that PSM is a human resource with dynamic properties organizations can cultivate to enhance productivity in public service workforces.