Some have viewed the progress of science through an evolutionary lens, with scientific knowledge being seen as evolving over time through a process of variation, selection and retention at multiple levels. Using an analogy with natural selection, Popper (1934) conceptualised a process in which competing theories or interpretations of the world around us, struggled for survival against others (Popper, 1934). Campbell (1974) viewed the scientific process occurring through variation, selection and retention. In this manner new variations of conceptualisations are first put forward. Less fit theories are winnowed out through the process of experiment and qualified prediction, and finally those more ‘fit’ theories are disseminated and retained throughout the scientific community. Toulmin (1972) further more specifically developed a population perspective, with competing concepts and beliefs struggling for survival within an ecology of research domains, with individual scientists and, importantly, scientific communities being the ‘carriers’ of such evolving components of knowledge. Through selective diffusion and retention some intellectual variants become more prominent in certain domains or population niches. In this sense Toulmin (1972) viewed the scientific process as a hierarchy of co-evolutionary systems. As such, an ecology of competing concepts evolves within more or less formally structured theories, alongside the evolution of a population of scientists within more or less formally organized institutions (Plotkin, 1994; Toulmin, 1972).