Recent evidence has shown that humans have a domain-specific competence for reasoning about the biological world - an intuitive biology. It is suggested that such an ability can be explained in terms of evolved psychological mechanisms designed to perceive and conceptually organise aspects of the natural world. Two studies were conducted to examine this concept in relation to children's understanding of two properties associated with living things: growth and movement. Four- and five-year old children viewed line drawings of animals, plants and artificial objects, and were subsequently asked questions relating to the capacity of each item to move and grow autonomously. As hypothesised, in both studies participants reported that plants and animals but not artefacts were capable of increasing in size over time, but that only animals were capable of self-generated movement. These results are consistent with the view that children possess specialised mechanisms for reasoning about the biological world. The implications of these findings are considered in terms of an evolutionary approach to intuitive biology.