or as inanimate objects (most plants) (Carey, 1985). An understanding of the biological world as a domain with its own principles is thought not to emerge until well into the elementary school years (Carey, 1985, 1988). Animals are distinctive only insofar as they are also understood as social agents with desires, goals, and other cognitive and emotional states that help explain their actions. Since young children will often attribute properties to animals on the basis of their psychological similarities to humans (e.g., dogs eat but worms do not because eating is understood as feeling hungry and feeling satiated or as requiring a clearly visible mouth), they often mistakenly underattribute biological properties to simpler organisms in both the animal and plant kingdoms (Carey, 1985, 1988).

Young children can also be remarkably ignorant about many of the mechanisms that underlie biological processes, such as digestion, movement, and reproduction. Thus, preschoolers may grossly misconstrue the inner workings of the body that digest food; they have little sense of how the body breaks down food into simpler compounds through mechanical and chemical means (Gellert, 1962; Nagy, 1953). Similarly, they have no sense of how organic molecules release energy units that are used to contract muscles and enable movement. Nor do most children know about sex gametes, how they come into contact, and how they result in a fertilized egg that differentiates into a fetus. Because of these clear deficits, it is easy to infer that young children have no understanding of the living world. Moreover, their tendency in some contexts to generalize properties based on psychological similarity suggests that they might be understanding biological entities and processes in psychological terms.

At a different level, however, there is considerable evidence suggesting more precocity in children’s abilities to track the distinctive nature of causal and relational patterns in the biological world (Inagaki and Hatano, 2006; Keil, 2003). Consider again the case of digestion. Although young children do not understand the physiology of digestion in any sort of detail, they do seem to figure out early on that food is transformed in some manner that gives organisms the ability to grow and to move (Inagaki and Hatano, 2002). They understand that an organism will physically deteriorate if it cannot ingest food, they know that the transformation of food is essential to its being usefully employed by the body, and they know that only plants and animals transform food and need to digest it (Toyama, 2000). It therefore seems that, at a more abstract functional level, preschoolers do have a sense of some of the distinctive operations and processes that are essential to digestion. In that way, they are not so different from adults. Most adults also have poor or mistaken knowledge of biological mechanisms, believing for example that most of the solid mass of plants arises from the soil, often completely missing the huge contribution from gaseous carbon dioxide (Driver et al., 1994). At this mechanistic level of analysis, one can find a huge array



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