Reasoning from a naturalistic perspective, viewing the mind as an evolved biological organ with a particular structure and function, a number of influential philosophers and cognitive scientists claim that science is constrained by human nature. How exactly our genetic constitution constrains scientific representations of the world remains unclear. This is problematic for two reasons. Firstly, it often leads to the unwarranted conclusion that we are cognitively closed to certain aspects or properties of the world. Secondly, it stands in the way of a nuanced account of the relationship between our cognitive and perceptual wiring and scientific theory. In response, I propose a typology or classification of the different kinds of biological constraints and their sources on science. Using notion of a conceptual space, I distinguish between constraints relating to the ease with which we can reach representations within our conceptual space (which I call ‘biases’) and constraints causing possible representations to fall outside of our conceptual space. This last kind of constraints does not entail that some aspects or properties of the world cannot be represented by us – as argued by advocates of ‘cognitive closure’ – merely that some ways of representing the world are inaccessible to us. It relates to what and have framed as ‘the alien scientist hypothesis’ (the possibility that alien scientists, endowed with radically different cognitive abilities, could produce representations of the world that are unintelligible to us). The purpose of this typology is to provide some much needed clarity and structure to the debate about biological constraints on science.