The rise of experimentation and the decline of natural history constitute the historiographic backbone to most narratives about the history of the life sciences in the twentieth century. As I argue here, however, natural history practices, such as the collection and comparison of data from numerous species, and experimental practices have actually converged throughout the century, giving rise to a new hybrid research culture which is essential to the contemporary life sciences. Looking at some examples of researchers who studied experimentally the relationships between organisms offers a unique window into how the norms, values, and practices of natural history entered the laboratory and, conversely, how the norms, values, and practices of experimentation transformed natural history. This paper concentrates on a largely overlooked episode in the history of the life sciences: the development of Alan A. Boyden's serological taxonomy. In the United States, from the late 1920s to the early 1960s, he was the most prominent advocate of this experimental approach in natural history. His quest for an objective method to understand the relationships among species, his creation of a serological museum where he could apply his comparative perspective, and his continued negotiations between natural historical and experimental traditions, illustrate the rise of a new hybrid research culture in the twentieth century. It also helps us solve a historiographic puzzle, namely how biological diversity become so central in the experimental life sciences, i.e., in a tradition which we generally understand as having focused on a few model organisms, and which relegated the study of biodiversity to naturalists and their museums.