Two kinds of evolutionary individuals: the concept of common interest as an evolutionary foundation of dualism on biological individuality

What is a biological individual? This is a question that has been of interest to biologists and philosophers for a long time. The usual response is an attempt either to find a single, unifying concept (a monistic stance) or to justify the existence of multiple concepts, for instance, by referring to scientific practice (a pluralistic stance). In this paper, I adopt a pluralistic stance and focus on evolutionary studies. I argue that in the context of evolutionary biology we need to distinguish between two kinds of evolutionary individuals, based on the concept of common interest. I decouple this into common interest by necessity (CIN) and common interest by contingency (CIC), and argue that this division corresponds to two kinds of evolutionary individuals. To situate the framework I thus develop within the context of ongoing discussions, I then compare it with frameworks corresponding to other concepts commonly found in the relevant literature, such as those concerning units of selection and agency. The conclusion is that the ontology of evolutionary biology is more complex than often assumed, and that we should distinguish: units of selection, agents, and two kinds of evolutionary individuals.