Essentialism in Everyday Thought
The following observations may seem wholly unrelated, but all can be understood within a framework of psychological essentialism:
The president of Harvard recently suggested that the relative scarcity of women in "high-end" science and engineering professions is attributable in large part to male-female differences in intrinsic aptitude (Summers, 2005).
In a nationally representative survey of Black and White Americans, most adults agreed with the statement, "Two people from the same race will always be more genetically similar to each other than two people from different races" (Jayaratne, 2001).
Nearly half the U.S. population reject evolutionary theory, finding it implausible that one species can transform into another (Evans, 2001).
A recent study of heart transplant recipients found that over one third believed that they might take on qualities or personality characteristics of the person who had donated the heart (Inspector, Kutz, & David, 2004). One woman reported that she sensed her donor's "male energy" and "purer essence" (Sylvia & Novak, 1997; pp. 107, 108).
It is estimated that roughly half of all adopted people search for a birth parent at some point in their lives (Müller & Perry, 2001).
People place higher value on authentic objects than exact copies (ranging from an original Picasso painting to Britney Spears's chewed-up gum; Frazier & Gelman, 2005).
Essentialism is the view that certain categories (e.g., women, racial groups, dinosaurs, original Picasso artwork) have an underlying reality or true nature that one cannot observe directly. Furthermore, this underlying reality (or "essence") is thought to give objects their identity, and to be responsible for similarities that category members share. Although there are serious problems with essentialism as a metaphysical doctrine (Mayr, 1991), recent psychological studies converge to suggest that essentialism is a reasoning heuristic that is readily available to both children and adults. In this piece I review some of the evidence for essentialism, discuss the implications for psychological theories, and consider how language influences essentialist beliefs. I conclude with directions for future research.
Evidence for psychological essentialism
Medin and Ortony (1989) suggest that essentialism is a "placeholder" notion: one can believe that a category possesses an essence without knowing what the essence is. For example, a child might believe that there exist deep, non-obvious differences between males and females, but have no idea just what those differences are. The essence placeholder would imply: that category members are alike in unknown ways, including a shared underlying structure (examples b, d, and f above); that there is an innate, genetic, or biological basis to category membership (examples a, b, and e above); and that categories have sharp and immutable boundaries (examples b and c above). Elsewhere I have detailed at length the evidence that preschool children expect certain categories to have all of these properties (Gelman, 2003, 2004). Here I briefly illustrate with two examples: innate potential and underlying structure.
Innate potential. One important kind of evidence for essentialism is the belief that properties are fixed at birth (also known as innate potential). To test this notion, researchers teach children about a person or animal that has a set of biological parents and then is switched at birth to a new environment and a new set of parents. Children are then asked to decide whether the birth parents or the upbringing parents determine various properties. For example, in one item set, children learned about a newborn rabbit that went to live with monkeys, and were asked whether it would prefer to eat carrots or bananas, and whether it would have long or short ears (Gelman & Wellman, 1991). Preschool children typically report that it prefers carrots and has long ears. Even if it cannot eat carrots at birth (because it is too young), and it is raised by monkeys that don't eat carrots, and it never sees another rabbit, eating carrots is inherent to rabbits; this property will eventually be expressed. Although there is debate as to when precisely this understanding emerges, even on a conservative estimate it appears by about 6 years of age. Intriguingly, for some categories children are more likely than adults to view properties as innately determined. For example, 5-year-olds typically predict that a child who is switched at birth will speak the language of the birth parents rather than the adoptive parents (Hirschfeld & Gelman, 1997). Beliefs about birth and reproduction vary widely across cultures; nonetheless, Torguud adults in Western Mongolia (Gil-White, 2001), upper-caste adults in India (Mahalingam, 2003), Vezo children in Madagascar (Astuti, Carey, & Solomon, 2004), and Itzaj Maya adults and children in Mexico (Atran, Medin, Lynch, Vapnarsky, Ek', & Sousa, 2001) all display a nativist bias.
Underlying structure. When forming categories, children readily consider properties beyond those that are superficial or immediately apparent. They pay close attention to internal parts and hidden causes (Diesendruck, 2001; Gopnik, Glymour, Sobel, Schultz, Kushnir, & Danks, 2004). Preschool children infer that properties true of one category member will extend to others of the same category, even when these properties concern internal features and non-visible functions, and even when category membership competes with perceptual similarity. For example, preschool children infer that a legless lizard shares more non-obvious properties with a typical lizard than a snake, even though the legless lizard and the snake look much more alike (Gelman & Markman, 1986; Jaswal & Markman, 2002). Under certain conditions, young children also recognize that an animal cannot be transformed into another kind of thing (for example, a raccoon cannot become a skunk; Keil, 1989). Instead, category membership is stable over striking transformations-as long as the insides remain the same.
Implications of psychological essentialism
Childhood essentialism poses a challenge to traditional theories of children's concepts, which emphasized their focus on superficial, accidental, or perceptual features. Many scholars have proposed one or another developmental shift with age: from concrete to abstract, from surface to deep, or from perceptual to conceptual. In contrast, essentialism points out that abstract, non-obvious features are important to children's concepts from a remarkably young age. Rather than developmental shifts, there are remarkable commonalities between the concepts of children and those of adults. However, essentialism does not suggest that perceptual features or similarity are unimportant to early concepts. Even within an essentialist framework, appearances provide crucial cues to an underlying essence. Similarity appears to play an important role in fostering comparisons of representations and hence discovery of new abstractions (Namy & Gentner, 2002). Rather than suggesting that human concepts overlook perception or similarity, essentialism assumes that a category has two distinct though interrelated levels: the level of observable reality and the level of explanation and cause.
It is this two-tier structure that may serve to motivate further development. Most developmental accounts of cognitive change include something like this structure, such as equilibration, competition, theory change, analogy, or cognitive variability (see Gelman, 2003, for review). In all these cases, as with essentialism, children consider contrasting representations. When new evidence conflicts with the child's current understanding, this can lead the child gradually to construct new representations. Indeed, targeted interventions that introduce a non-obvious similarity between dissimilar things can lead to dramatic change in children's concepts (Opfer & Siegler, 2004). Perhaps not surprisingly, then, children look beyond observable features when trying to understand the categories of their world. In positing a reality beyond appearances, the search is on for more information, deeper causes, and alternative construals.
Psychological essentialism also has implications for models of categorization. There is an idealized model of categorization that has formed the basis for much work in psychology. Standard theories of concepts have been based on considering which known properties are most privileged, and in what form. In contrast, essentialism tells us that known properties do not constitute the full meaning of concepts. Concepts are also open-ended. They are in part placeholders for unknown properties.
Furthermore, it has often been assumed that there is a single, unitary process of categorization (Murphy, 2002). Yet an essentialism perspective, with its focus on both outward and underlying properties, suggests that categorization is more complex: Categorization serves many different functions, and we recruit different sorts of information depending on the task at hand. Rapid identification calls for one kind of process; reasoning about genealogy calls for another. Task differences yield different categorization processes (Rips, 2001). Even when the task is restricted to object identification, people make use of different sorts of information depending on the task instructions (Yamauchi & Markman, 1998).
Language and Essentialism
Essentialist beliefs are influenced by the language that children hear. Nouns imply that a category is relatively more stable and consistent over time and contexts than adjectives or verb phrases. For example, in one study (Gelman & Heyman, 1999), 5- and 7-year-old children first learned about a set of individuals with either a noun ("Rose is 8 years old. Rose eats a lot of carrots. She is a carrot-eater.") or a verb phrase ("Rose is 8 years old. Rose eats a lot of carrots. She eats carrots whenever she can."). They were then probed for how stable they thought this category membership would be across time and different environmental conditions (e.g., "Will Rose eat a lot of carrots when she is grown up?" "Would Rose stop eating a lot of carrots if her family tried to stop her from eating carrots?"). Children who heard the noun "carrot-eater" were more likely than children who heard the verbal phrase "eats carrots whenever she can" to judge that the personal characteristics would be stable over time and adverse environmental conditions. (For other examples of noun labeling effects, see also Walton & Banaji, 2004; Waxman, 2003; Xu, 2002.)
Another important linguistic device is the generic noun phrase, which refers to a category rather than a set of individuals (e.g. , "Cats see well in the dark" is generic; "These cats see well in the dark" is not). Generics express essential qualities and imply that a category is coherent and permits category-wide inferences (Carlson & Pelletier, 1995; Prasada, 2000). When 4-year-old children hear a new fact in generic form (e.g., "Bears have 3 layers of fur"), they treat this fact as typically true of most or all category members (Gelman, Star, & Flukes, 2002). Generic nouns are plentiful in the speech that children hear (Gelman, Coley, Rosengren, Hartman, & Pappas, 1998; Gelman, Taylor, & Nguyen, 2004), and children are highly sensitive to formal linguistic cues that mark whether or not an utterance is generic (e.g., "Birds fly" vs. "The birds fly"; Gelman & Raman, 2003). Additionally, there are language-specific devices that convey essentialism. For example, young Spanish-speaking children make inferences about the stability of a category based on which form of the verb "to be" is used to express it (ser versus estar; Heyman & Diesendruck, 2002). Although it is unlikely that language is the source of psychological essentialism, it provides important cues to children regarding when to treat categories as stable and having an intrinsic basis.
Preschool children and adults from a variety of cultural contexts expect members of a category to be alike in non-obvious ways. They treat certain categories as having inductive potential, an innate basis, stable category membership, and sharp boundaries. The implications of essentialism span widely, as seen in the examples that started this piece. Essentialized categories include not only biological species, but also social categories and traits (Giles, 2003; Heyman & Gelman, 2000a, 2000b; Yzerbyt, Judd, & Corneille, 2004; Haslam, Bastian, & Bissett, 2004). These beliefs are not the result of a detailed knowledge base, nor are they imparted directly by parents, although language may play an important tacit role. Instead, they appear early in childhood with relatively little direct prompting.
Although I have provided a framework of "psychological essentialism" to account for these data, numerous questions and debates remain unresolved. To what extent is essentialism a single, coherent theory, as opposed to a disparate collection of beliefs? Do people invoke essences per se, or something less committal (Strevens, 2000; Ahn, Kalish, Gelman, Medin, Luhmann, Atran, Coley, & Shafto, 2001)? Why do children often appear to rely on superficial features, despite their sensitivity to non-obvious properties in the tasks described here (e.g., Sloutsky, 2003; Smith, Jones, & Landau, 1996)? Some scholars have argued that essentialism cannot account for certain experimental findings regarding adult word meaning (Malt, 1994; Sloman & Malt, 2003; Braisby, Franks, & Hampton, 1996). For example, the extent to which different liquids are judged to be water cannot be fully explained by the extent to which they share the purported essence of water, H2O. Whether these findings undermine (or even conflict with) psychological essentialism is a matter of current debate (Gelman, 2003; Rips, 2001).
Many questions remain for future research. Ongoing investigations examine: developmental antecedents to essentialism in infancy (Graham, Kilbreath, & Welder, 2004; Welder & Graham, in press), the relation between perceptual and conceptual information in children's categories (Rakison & Oakes, 2003), individual differences in essentialism (Haslam & Ernst, 2002), contexts that foster or inhibit essentialism (Mahalingam, 2003), links to stereotyping or prejudice (Bastian & Haslam, in press), and how best to model these representations in formal terms (Ahn & Dennis, 2001; Rehder & Hastie, 2004).
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