more, without an atomic-molecular level of description, it is hard to understand what cells are doing (to understand cellular metabolism, etc.). They may have an anthropomorphic view of cells as making decisions and see the nucleus as directing all cell processes. They may also see cells as engaging in miniature versions of macroscopic processes. For example, they think of nutritive processes in cells as analogous to macroscopic digestive processes where food is ground and processed; or they confuse cellular respiration with macroscopic processes of breathing (Flores, Tovar, and Gallegos, 2003). Thus, they lack distinct descriptions of processes at the atomic-molecular and cellular levels that would provide deeper, mechanistic explanations for macroscopic phenomena. Overall, they seem to retain a simple macroscopic conception of the workings of the human body—and a very limited one at that.

At a more systemic level, children’s understanding of the origin of living things undergoes considerable change. Between about 8 and 10 years of age, children develop a more explicit creationist explanation of the origins of species, regardless of beliefs in their homes (Evans, 2001). Such beliefs may reflect the formation of an explicit theory based on their initial essentialist bias—that is, their initial tendency to believe that things have a true underlying nature. Thus, a belief that species have fixed essences works against the necessary concept of a species as a probabilistic distribution of traits on which natural selection operates. That essentialist bias, however, is not merely a problem confronted by children. Indeed, it has been argued that the relatively late emergence of evolutionary theory in the history of science was because of the essentialist biases in most adult theories of species (Hull, 1965; Mayer, 1982), leading one scholar to remark that essentialism had resulted in a “2000 year stasis” in evolutionary thought.

This continuing difficulty with evolutionary thought in adulthood is also borne out in work showing that college-educated adults also frequently answer questions about evolution and natural selection in ways that are not in accord with evolutionary theory (Shtulman, 2006). Thus, essentialist biases can distort judgments about a wide range of evolutionary phenomena, including variation, inheritance, adaptation, domestication, speciation, and extinction (Shtulman, 2006). It may also be the case that evolutionary thought is hampered in childhood and beyond by another bias that emerges in the first year of life, that of seeing intentional agents as the only plausible causes of ordered relationships in the world (Newman et al., 2006). When tested as to whether an inanimate entity, such as the wind, or an animate one, such as a person, could cause a disordered array to become ordered, 1-year-olds and preschoolers strongly prefer the animate agent, while showing no preference when the situation is reversed, that is, the cause of an ordered array becoming disordered. This bias may be related to the argument from design, a centuries-old belief that the elaborate functional structure of the living



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