preschoolers' ability to distinguish living kinds as a function of

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Preschoolers' Ability to Distinguish Living Kinds as a Function of Regrowth

Andrea G. Backscheider, Marilyn Shatz, and Susan A. Gelman University of Michigan

BACKSCHEIDER, ANDREA G.; SHATZ, MARILYN; and GELMAN, SUSAN A. Preschoolers' Ability to Distinguish Living Kinds as a Function of Regrowth. CHILD DEVELOPMENT, 1993, 64, 1242-1257. In order to acquire a theory of biology, children must acquire knowledge about living kinds. Although many studies have shown that preschool children do not accurately classify living kinds and do not use appropriate properties when asked to decide whether something is a living kind, recent work has shown that 3- and 4-year-olds do know something about biological growth. The ability of kinds to heal through regrowth was used in this paper as a measure of children's implicit understanding that plants and animals can be grouped together. In 3 experiments, children were told that animals, plants, and artifacts had been damaged and were asked whether the objects could heal through regrowth and whether a person could mend them. In all studies, children were sensitive to ontological kind. 4-year-olds realized that both plants and animals can regrow but that artifacts must be fixed by human intervention. 3-year-olds were less knowledgeable but did realize that artifacts cannot regrow. Overall, children showed some biological knowledge, implicitly grouping plants and animals together and differentiating them from artifacts.

Why do tables have legs? Why do dogs have lungs? Adults answer questions like these with the theories they hold. They can figure out that tables must have legs in order to stand at a proper height and that dogs must have lungs in order to breathe. By using the information contained in naive biological and physical theories, adults are able to account for the characteristics that objects have and to predict events in the world around them. For the most part, adults know what theoretical domain objects and events belong to and what kinds of explanations are sensible for answering different questions. Adults do not attempt to explain why a dog has lungs in terms of mathematical principles; rather, they appeal to biological principles. The possession of theories along with knowledge about their applicable domains allows explanation and induction from known facts.

An increasing amount of research suggests that even preschool children have the start of several theories about the world (Wellman & Gelman, 1992), such as a naive psychology (Wellman, 1990), a naive biology

(Inagaki & Hatano, 1988; Keil, 1989), and a naive physics (Spelke, 1990). One important question, then, is how children make the distinctions ultimately needed for these theories. Eventually, children must recognize the living-nonliving distinction, the artifact- natural kind distinction, the animate- inanimate distinction, and the physical- nonphysical distinction, to name a few. This paper examines whether preschoolers group plants and animals into living kinds by fo- cusing on the role human beings play in the repair and regrowth of living kinds and artifacts.

On the way to developing the kinds of distinctions needed for mature theories, children may recognize other dichotomies based on salient properties or partial knowledge. Children may first realize that plants and animals are both living kinds by con- trasting them with artifacts. Two salient characteristics on which living kinds differ from artifacts are growth and dependence on natural, not intentional, cause. For example, chipmunks, but not tables, grow, and human beings can make tables, but not chipmunks.

This research was supported in part by an NSF Predoctoral Fellowship to Andrea Back- scheider, and an NSF Faculty Award for Women Scientists and Engineers, BNS 9100348, to Susan Gelman. We thank Anne Hickling, Charles Kalish, and Allison Young for their helpful comments. We also thank J. E. Keith Smith for his statistical advice. We are grateful to the children, teachers, and staff of the University of Michigan Children's Centers for their generous cooperation. Address for correspondence: Andrea G. Backscheider, Department of Psychology, 3433 Mason Hall, University of Michigan, Ann Arbor, MI 48109-1027.

[Child Development, 1993, 64, 1242-1257. ? 1993 by the Society for Research in Child Development, Inc. All rights reserved. 0009-3920/93/6404-0018$01.00]

Backscheider, Shatz, and Gelman 1243

To begin to address the question of whether children can group plants and animals into living kinds, we review research on three issues: whether children understand what it means to be "alive," what children understand about growth, and whether children realize that living kinds are subject to biological cause.

Previous research showed that children under 10 may not understand what it means to be a living thing (Carey, 1985). Piaget (1929) claimed that young children do not map the word alive onto the adult category; instead, children progress from having no concept of what it means to be alive to using movement as a criterion and finally to set- tling on the adult concept during the late elementary school years. Thus, he found that young children do not believe that plants are alive, but they do believe that the sun is alive. Carey (1985) reexamined this phe- nomenon and found that, when asked if something was alive, preschool children drew the living kind boundary either too widely or too narrowly. Some children did say that plants are alive, but those who attributed life to plants also attributed life to inanimate objects. However, Gelman, Spelke, and Meck (1983) found that by age 4 children knew whether a few common objects, like rocks and people, are alive. It seems that young children may have only rote knowledge of which objects are, or are not, alive.

Other tasks confirm that young children do not group plants and animals into one coherent category when making judgments about life or about biological properties. Richards and Siegler (1986) found that 4- year-olds who were asked for characteristics of living things gave attributes that are true of animals but not of plants. When asked to decide whether things from another planet were alive, children relied on properties true of animals, not living kinds in general. Stavy and Wax (1989) asked 6-15-year-olds to classify animals, plants, and nonliving things according to whether they were living and according to whether they possessed specific biological properties such as breath- ing, eating, and reproducing. The researchers reported that only 30%-60% of 6-11- year-olds correctly classified plants as living things. Although children's beliefs about the biological properties of animals were related to classification of animals as living things, their beliefs about the biological properties of plants bore little relation to their living/ nonliving status. Keil (1989) found that kin-

dergartners did not realize the privileged status of insides and parentage over behav- ior and appearance in determining the identity of plants and animals. Second graders, however, realized that insides and parentage are more important to the identity of plants and animals than is appearance. Overall, young children showed little evidence of a living kinds category and little understanding of some of the biological properties of plants.

Children also fail to use a living kinds category implicitly in inductive reasoning. Carey (1985) told 6-year-olds that one of three sets of things had golgi: (a) a dog and a bee, (b) a dog and a flower, or (c) a flower. Carey then asked whether other animals, artifacts, and astronomical objects also had golgi. Only children who had been taught that both a dog and a bee have golgi showed any evidence that a living kind concept constrained their inductions. Overall, only four out of 59 children attributed golgi to all living kinds and only living kinds. Based on these and other similar experiments, Carey argued that preschool children use naive psychology, not naive biology, when making inferences about animals; an adultlike understanding of animals and living kinds seems to develop relatively late in the elementary school years. In sum, in previous tasks preschool children have shown no evidence of a living kinds category.

Nonetheless, other research suggests that children have knowledge about some of the properties that separate living things from nonliving things. First, children know something about animal growth and something about plant growth. Rosengren, Gel- man, Kalish, and McCormick (1991) tested 3-6-year-old children's beliefs about growth and change in animals and artifacts. They found that even 3-year-olds expected change to be orderly, constrained, domain specific, and mechanism specific. For example, children expect animals, but not artifacts, to grow bigger, not smaller. The youngest children did not, however, display a clear understanding of the kinds of changes artifacts may undergo. Inagaki and Hatano (1987, 1988) demonstrated that 5-6-year-old children realize that living things grow because they take in food, not because they want to, and 4- and 5-year-olds realize that animals' physical change (weight change) is affected by food intake, not intention and desire. Finally, preschoolers know that both plants and animals grow; older 4-year- olds also know that different factors affect

1244 Child Development their growth. Hickling and Gelman (1992) showed 4-year-olds pictures of plants and animals and asked them questions about growth. They found that older 4-year-olds know the different properties that char- acterize animal growth and plant growth. Younger 4-year-olds answered accurately when asked questions about animal growth and knew that plants need sunshine to grow but responded to other questions about plant growth on analogy to animal growth. The younger children expected plant growth to follow the same laws as animal growth. Overall, then, 4-year-olds know that both plants and animals grow, and demonstrate some awareness of the characteristics of growth.

In addition, preschoolers may understand that both plants and animals are subject to biological causes. Gelman (1988) found that 4-year-old children can sort objects according to whether they are made by human beings (see also Keil, 1989). As mentioned above, Inagaki and Hatano (1988) demonstrated that 4- and 5-year-olds realize that animals' physiological mechanisms are relatively independent of intention. In a set of studies, Springer and Keil (1991) found that 4- and 5-year-olds prefer natural mechanisms to explain color inheritance in plants and animals but realize the importance of human intervention in producing the color of artifacts. In sum, preschoolers may realize that biological mechanisms are central to both plants and animals whereas human intention is central to artifacts (see also Gel- man & Kremer, 1991).

Overall, early research suggested that preschool children do not know what it means to be alive and that they have little idea of what kinds of things possess biological properties; later research, however, suggests that children know something about growth, an important biological property, and something about biological cause. It seems that preschool children are just beginning to separate biological kinds from nonbiological kinds; they may be noticing and learning about the properties and characteristics of living kinds before they have an ex- plicit concept of living kinds.

The present research investigates an early understanding children may have about the commonalities of plants and animals. To form a living kinds category, children must group plants and animals together based on largely nonobvious properties (e.g., inheritance); this formation may be dif-

ficult for preschoolers who have little biological knowledge, especially of plants. However, children know something about growth in plants and animals, and know that the functioning of plants and animals is affected by biological cause, not human intent. These characteristics of plants and animals may provide a means by which children first distinguish living things from nonliving things. Healing and regrowth embody both of these processes. Living things must regrow to heal, whereas artifacts must be fixed by a person. Children have some early experience with phenomena such as these, possi- bly noticing that people play less of a role in the regrowth of animals and plants than they do in the transformations of artifacts. Thus, questions about the regrowth process of living kinds and artifacts may tap into children's early knowledge about living kind categories. Earlier studies may have under- estimated preschoolers' understanding of commonalities in plants and animals because they did not focus on this potential knowledge base for it.

The present studies asked whether children realize that both animals and plants regrow whereas artifacts must be mended by people. Children were told that various living kinds and artifacts had been altered and were asked how the items could be mended. For living kinds, the remedy must take place naturally, through regrowth. For artifacts, a person must fix the object. If children know this, they should be able to treat animals and plants alike: they should respond similarly to questions about plants and animals and differently to questions about artifacts.

Experiment 1 Method

Subjects.-Twenty-four 4-year-olds (M = 4-7, range = 4-2 to 5-0, 12 males, 12 females) were recruited from a university preschool. The children represent a racially mixed but primarily Caucasion middle-class population.

Materials.-Each subject was asked about the repair of 14 items. The stimulus set consisted of line drawings mounted on 4-inch x 6-inch index cards. Eight of the pictures included items with a part cut off, four living kinds (two plants and two animals) and four artifacts. In each picture the part was clearly separated from the rest of the object. The remaining six items were objects pictured with a clear scratch, four living kinds (two plants and two animals) and two

Backscheider, Shatz, and Gelman 1245 artifacts. A complete item list is given in Ta- ble 1 and sample items are pictured in Fig- ure 1.

Procedure.-The children were tested individually at the preschool. Children were brought to a quiet room and told, "I'm going to show you some pictures and ask you about them. Some questions might be hard, so just think carefully and do your best." Children were shown the 14 stimuli in random order and were asked two questions for each picture. One question concerned whether the object could regrow, and one question concerned whether a person could mend the object. For the "cut" items-the items that had a part of the object disconnected from the main body-children were shown the picture and told, "Look what happened! The y was cut off the x!" The regrowth question was then, "Do you think the x could grow another y ?" The person-mend question was, "Do you think a person could put the y back on the x?" After each answer children were asked for a justification. For example, for the rose cut off the bush the child would hear, "Look what happened! The rose was cut off the rosebush! Do you think the rosebush could grow another rose? Why is that? Do you think a person could put the rose back on the rosebush? Why is that?"

For the scratched items, the child was shown the picture and told, "Look what happened! The x was scratched!" The regrowth question was then, "Do you think the scratch could get better by itself?" The person-mend question was, "Do you think a person could make that scratch better?" Again, after each answer children were asked for justifications. For example, for the

TABLE 1 ITEMS USED IN EXPERIMENT 1

Item Description

Dog with its hair cut Hand with a fingernail cut Rose cut from a plant Grass mowed from a lawn Doll with its hair cut Television with an antenna cut Button cut off a shirt Table with a leg cut off Woman's hand scratched Cat with a scratch on its side Tomato plant with a scratched tomato Tree with its trunk scratched Chair with its seat scratched Car with a scratched side

scratched car, the child would hear, "Look what happened! The car was scratched! Do you think the scratch could get better by itself? Why is that? Do you think a person could make the scratch better? Why is that?" Whether a child first heard the regrowth or person-mend question was chosen randomly for each child, but then the child heard the same question first for all items.

Results The analyses below are designed to an-

swer three questions. First, we conducted a preliminary analysis to determine whether children treated plants and animals differently. Because we found no differences between the children's scores for plants and animals, we combined them for subsequent analysis. Second, we conducted an overall analysis to determine whether children treated living kinds (plants and animals) and artifacts differently from one another for the two questions and transformations. This issue was analyzed first at the group level, with an ANOVA, and then at the individual level, with binomial tests against chance. Fi- nally, we examined the children's justifications for information they might add about their knowledge of the living kind-artifact distinction.

Plants versus animals.-We first examined the hypothesis that children would respond similarly to the plant and animal questions. Because we had a maximum of only two responses per living kind type, in- sufficient for an ANOVA, we used a McNemar chi-square for this analysis. The McNemar chi-square tests the hypothesis that the probability of a child getting a cer- tain score for animal items is equal to the probability of the child getting that same score for the plant items (see Conover, 1980). The test would be significant if children consistently scored higher on plants than animals or consistently scored higher on animals than plants.

Because children may have performed differently on the cut and scratch transformations, we analyzed the responses for these transformations separately. Similarly, within each transformation, we analyzed the responses to each question separately. The McNemar chi-square requires categorical data; specifically, the number of children scoring higher on animals than plants and the number of children scoring lower on animals than plants. Thus, children were given scores representing how many yeses (0-2) they gave to each type of question of each

1246 Child Development

FIG. 1.-Sample items from Experiment 1

transformation type, first for the animal items and then for the plant items. Children were coded as positive if they received a higher score for animals than plants, and negative if they received a higher score for plants than animals. McNemar tests showed that there were no significant differences between children's answers for the plant and the animal items for any question type in either the cut or scratch transformation (X2's (1) < .91, p's > .30). Thus, we conclude that children responded similarly to the plant and animal questions and have combined these categories in the subsequent analyses.

Living kinds versus artifacts.-We then performed an ANOVA in order to determine how the children's answers were affected by the kind, the transformation type, or the agent responsible for mending. We performed a 2 (kind: living vs. artifact) x 2 (transformation type: cut vs. scratch) x 2 (agent: person vs. regrowth) repeated- measures ANOVA on the number of "yes" responses.' The ANOVA yielded a transformation x agent x kind interaction, F(1, 22) = 30.14, p < .001, a transformation x agent interaction, F(1, 22) = 4.96, p < .05, and an agent x kind interaction, F(1, 22) = 56.45, p < .001. There was a main effect of kind, F(1, 22) = 10.99, p < .005.

Children performed somewhat differently on the two transformations. For the cut transformation, planned contrasts showed that children were more likely to say that living kinds can regrow than that artifacts can regrow, F(1, 23) = 127.98, p < .001.

Likewise, children were more likely to reply that artifacts can be mended by people than that living kinds can be, F(1, 23) = 63.77, p < .001. Moreover, contrasts showed that children were more likely to say that artifacts can be mended by people than to say that they can regrow, F(1, 23) = 89.92, p < .001, and more likely to say that living kinds can regrow than to say they can be mended by people, F(1, 23) = 96.35, p < .001. Fur- ther, all means for the cut questions were significantly different from chance (see Ta- ble 2).

The results were not as clear for the scratch transformation, but planned contrasts showed that children also differentiated between living kinds and artifacts for the scratch transformation questions. Chil- dren were more likely to attribute regrowth to living kinds than to artifacts, F(1, 23) = 24.91, p < .001, and they were more likely to attribute mending by a person to an artifact than to a living kind, F(1, 23) = 11.07, p < .005. Finally, children were more likely to say that artifacts can be fixed by people than to say that they can regrow, F(1, 23) = 53.58, p < .001. There were no other significant differences; children were as likely to say that a scratched living kind can be mended by a person as to say it can regrow. On the scratch questions, the regrowth mean for artifacts was different from chance (see Table 2).

We next asked whether individual children answered the questions consistently. Performance significantly above chance (p

1 All the questions were scored from 0 to 4 except for the scratch transformation artifacts. These items were rescaled from a 0-2 scale to a 0-4 scale. Pilot testing showed that the children could handle only 14 items; thus we were forced to include only two scratched artifacts.


TABLE 2

PERCENT OF POSITIVE RESPONSES TO EACH QUESTION TYPE OF EXPERIMENT 1

QUESTION

TRANSFORMATION Person-mend Regrowth

Cut: Living ....................... .......... 18* (.19) 79* (.24) Artifact................... 68* (.30) 8* (.14)

Scratch: Living .................................. 42 (.31) 48 (.35) Artifact................... 63 (.34) 17* (.32)

NOTE.-Standard deviations are given in parentheses. * p < .001, different from chance by two-tailed t test.

< .05) as measured by a binomial test of the yes/no responses to the person-mend and regrowth questions required at least 13 of 24 children to get three or four out of four items in each category correct. For the artifact questions of the scratch condition children were only asked two questions. In this case above-chance performance required that 12 of 24 children get two out of two questions correct. As shown in Figure 2, children met the criterion for every question in the cut transformation. In the scratch transformation, children met the criterion for the person-mend question for living kinds and the regrowth question for artifacts.

Children's justifications.-We asked children for justifications in this experiment, but our use of the word "grow" in the original question may have made it difficult for children to provide adequate justifications. When asked to justify their responses to the regrowth questions, most children either did

not reply or did little more than repeat the word "grow." For example, children would justify their response to the question. "Why do you think the rosebush could grow another rose?" with the statement, "because it grows" or "because it doesn't grow." It is not clear whether the children would have mentioned biological growth on their own or whether we led them to it by explicitly mentioning growth in our question.

Nonetheless, the children gave many reasonable justifications. They used mechanical (giving a method of mending something) or practical (telling why a method works or not) justifications much more often on the person-mend questions than the regrowth questions (141 vs. 25 justifications) and much more often for the artifacts than for the living kinds (114 for six artifacts vs. 52 for eight living kinds). They said, for example, that you can't stick a dog's hair back on, or that it wouldn't work to glue a flower

24

22" Person-mend

"C 20 .A

Regrowth S 18

; 16 E 14

S 12 10 8-

o 6 S 4

" 2 z o

Living kind/Cut Artifact/Cut Living kind/Scratch Artifact/Scratch

Item type/Transformation FIG. 2.-The number of children meeting consistency criteria for each question, Experiment 1

1248 Child Development back on a plant. Also, although children had a tendency to say that people could heal scratches on living kinds, their justifications tended to be medical in nature; for example, "Well, he could put a band-aid on it," or "A doctor could do it." There were 24 medical justifications for living kinds and only five for the artifacts. Discussion

The results of this study demonstrate that 4-year-olds know something about the living kind-artifact distinction and about different types of transformations. Responses to the "cut" questions indicated that children know living things can heal through regrowth and that people can mend artifacts. Moreover, 4-year-olds know that artifacts do not heal through regrowth and that on the whole people cannot fix living things. Fur- thermore, by treating plants and animals similarly, children demonstrated at least prerequisites for a living kinds category. When asked about healing through regrowth and human intervention, children clearly separated plants and animals from artifacts.

The conclusions for the scratch transformation are much less clear. Most of the knowledge children had about this transformation seemed to revolve around artifacts. Children realized that artifacts cannot regrow but instead can be mended by people. However, children performed at chance on the plant and animal questions. These results are understandable, however, as it is not clear a scratch can be mended on a piece of fruit or plant. Once a piece of fruit is scratched, it remains so. Growing a new piece of fruit does not "mend" the old tomato, but growing a new rose does replace the old. At any rate, the differing response patterns for the cut and scratch transformations suggest that the results for "cut" are not due to a general response bias but, instead, are due to knowledge held by the child.

Finally, children's justifications indicate that they know something about possible remedies for living kinds and artifacts. Chil- dren not only answered correctly but also justified their answers reasonably. Children tended to mention specific methods of human intervention as artifact remedies and as ways a person can mend something; they mentioned these methods less often to explain living kind remedies and in response to regrowth questions. Children also gave medical remedies for living kinds, though it was not clear how much was attributed to

people and how much the child attributed to nature.

Experiment 2 In Experiment 1 the children's justifi-

cations suggested that they know something about how regrowth separates living kinds and artifacts. However, the questions children heard specifically mentioned growth. Thus, we may have unwittingly pointed the children to an important cue, thereby chan- neling their responses and limiting their justifications. In Experiment 2 we asked more general questions that did not specifically mention growth. In addition, we omitted the potentially confusing scratch questions. Fi- nally, because 4-year-olds did so well in Ex- periment 1, we included younger children among the subjects in Experiment 2. Method

Subjects.-Nineteen 3-year-olds (M = 3-7, range = 3-2 to 3-11, 11 girls and 5 boys) and 16 4-year-olds (M = 4-8, range = 4-3 to 5-0, 8 girls and 8 boys) were recruited from a university preschool. Three 3-year-old boys were dropped after showing a response bias, responding yes to every question. The children represent a racially mixed but primarily Caucasian middle-class population.

Materials.-The eight cut items from Experiment 1 were used.

Procedure.-With the exception of the wording of the questions, the procedure was identical to that of Experiment 1. In this experiment, children were told, "See this? This is an x, and the y is off the x." For all items except the rose and the shirt button, the regrowth question was then, "Do you think the y could get long by itself?" The person-mend question was, "Do you think a person could make the y long?" After each answer, the children were asked for a justification. For example, for the leg cut off the table, the child might hear, "Do you think the leg could get long by itself? Why is that? Do you think a person could make the leg long? Why is that?" For the rosebush and for the shirt, the regrowth question was, "Do you think the x could get another y by itself?" and the person-mend question was, "Do you think a person could get the x another y?" Again, after each answer, children were asked for justifications. Results

The analyses followed the same pattern as those of Experiment 1. We first examined whether 3-year-olds and, separately, 4-year-


olds treated the plant and animal items similarly. When there were no differences in the way children treated plants and animals, we conducted overall analyses examining the differences in their answers to living kinds and artifacts, both at the group and at the individual level. Finally, we analyzed the children's justifications for information they might add about children's knowledge of living kinds.

Plants versus animals.-We first examined whether 3-year-olds and 4-year-olds performed differently on the plant and animal questions. Because we thought that younger children might perform differently from older children, we analyzed the responses of the age groups separately. As in Experiment 1, children were given scores representing how many yeses (0-2) they gave to each type of question, first for the animal items and then for the plant items. Children were coded as positive if they received a higher score for animals than plants, and negative if they received a higher score for plants than animals. Be- cause McNemar chi-square tests require that the total number of children categorized as positive and negative be at least 10, and this criterion was not met, we instead conducted binomial tests to investigate whether children scored similarly on the animal and plant items (see Siegel & Castellan, 1988). Binomial tests indicated that 4-year-olds showed no significant differences between the plants and the animals for any question type (p's > .14). Three-year-olds' answers were not significantly different to the plant and animal items on the regrowth question (p > .49); on the person-mend question the 3-year-olds showed a trend (p < .10). Be-

cause neither age group showed significant differences in response to animal versus plant questions, we combined the plant and animal items.

Living kinds versus artifacts.-We next compared the children's responses to questions about artifacts versus living kinds. As in Experiment 1, children were given one point each time they answered "yes" to a question. We performed a 2 (age: 3-year-old vs. 4-year-old) x 2 (agent: person vs. regrowth) x 2 (kind: living vs. artifact) mixed ANOVA on the children's scores. The ANOVA yielded a group x agent x kind interaction, F(1, 30) = 47.12, p < .001, an agent x kind interaction, F(1, 30) = 97.36, p < .001, and a main effect for kind, F(1, 30) = 6.59, p < .05. There were no other significant effects or interactions. The means are given in Table 3. Planned contrasts showed that 4-year-olds are more likely to say that living kinds can regrow than to say that artifacts can regrow, F(1, 30) = 96.00, p < .001. They were also more likely to reply that people can mend artifacts than to say that people can mend living kinds, F(1, 30) = 32.77, p < .001. Similarly, 4-year-olds were more likely to say that people can mend artifacts than to say that artifacts can regrow, F(1, 30) = 52.23, p < .001, and were more likely to say that living kinds can regrow than to say they can be fixed by people, F(1, 30) = 28.4, p < .001. All means were different from chance.

Three-year-olds also treated living kinds and artifacts differently, but the effects were not as strong. The younger children were more likely to say that living kinds can regrow than can artifacts, F(1, 30) = 6.00, p < .05, and were more likely to say that arti-

TABLE 3 PERCENT OF POSITIVE RESPONSES TO EACH QUESTION TYPE OF

EXPERIMENT 2

QUESTION

AGE Person-mend Regrowth

4-year-olds: Living ....................................... 31* (.27) 86* (.20) Artifact ...................................... 78** (.27) 11** (.27)

3-year-olds: Living ....................................... 63 (.29) 58 (.40) Artifact ...................................... 66 (.34) 39 (.33)

NOTE.-Standard deviations are given in parentheses. * p < .05, different from chance by two-tailed t test. ** p < .001, different from chance by two-tailed t test.

1250 Child Development facts can be mended by people than that artifacts can heal through regrowth, F(1, 30) = 8.16, p < .01. None of the means differed significantly from chance (see Table 3).

We next asked how differently 3-year- olds answered from 4-year-olds. We performed Scheff6 contrasts on the means for each question and kind. Three-year-olds were significantly more likely than 4-year- olds to say that an artifact can regrow, F(1, 31) = 4.62, p < .05. There were no differences on the remaining questions.

As in Experiment 1, we asked whether individual children answered the questions consistently. Performance significantly above chance (p < .05), as measured by a binomial test of the yes/no responses to the person-mend and regrowth questions, required at least 10 of 16 children to get three or four out of four items in each category correct. The 4-year-olds were above chance for every question type, with from 10 to 15 children scoring three or four out of four. The 3-year-olds were not significantly different from chance for any question type.

Justifications.-Justifications were col- lected for both the 3- and 4-year-olds. The justifications were taped, transcribed, and coded into one of three categories: those referring to living-kind characteristics (LKC category), those referring to artifact characteristics (AC category), and "other" (see Table 4). The justifications in the LKC and AC categories were then coded as correct or incorrect. A justification was considered correct if it was possible or plausible. For example, children who said, "You can glue a TV antenna back on" were coded as correct, as were children who said, "You can't glue a TV antenna back on because the edges are too small-it won't stick." Also, a child who contradicted his original answer in the justification could be correct. For example, a child might answer no to "Could a person get the shirt another button?" but be scored correct for justifying with, "Well, I guess she could if she sewed it back on." We did not revise the yes/no score based on justifications, however. After the initial coding, 33% of the justifications were also coded by a second coder. Reliability was 98% for the justi-

TABLE 4 CATEGORIES USED FOR CODING CHILDREN'S JUSTIFICATIONS, EXPERIMENT 2

Code Criterion Example

Living-kind characteristics: Alive ..................................... The child mentions the word Dolls aren't alive.

"alive." Real ........................................ The child mentions the word Because it's not real.

"real." Grow ............................................ The child mentions the word Because it will grow back.

grow. Movement................................. The child mentions spontane- No, because it can't walk.

ous movement. Human parts ............................ The child mentions presence or The shirt can't get a new but-

absence of a body part. ton because it has no arms.

Artifact characteristics: Person crucial ..... .............. The child indicates a person or Because a person needs to

some person-like quality is fix it. necessary.

Mechanical .............................. The child indicates a specific You could fix it with mechanism for a repair. superglue.

Practical ................................... The child mentions practical Because you can't find a considerations, but no mech- new skin. anism.

Other: Growth conditions .................. The child mentions the condi- You need to water it.

tions under which growth is possible.

Categorization ......................... The child invokes a category. It's like all furniture. God ...................................... The child indicates God is A person can't, but Jesus

needed. can. Medical .................................... The child mentions medical Put a bandaid on it.

remedy.

Backscheider, Shatz, and Gelman 1251 fication category (e.g., AC) and 96% for whether the justification was correct.

Before reporting the findings, we con- sider what constitutes a reasonable pattern of responses. Children should justify yes and no answers differently. When the answer is yes, children should explain what characteristics of an object enable a person to fix the object or enable the object to regrow. When children answer no, they can justify their answers either by explaining which of the object's characteristics make it impossible for the mending or regrowth to happen or by telling the experimenter what other property would be necessary for regrowth to take place. Thus, it is reasonable to expect the children's justifications for yes answers to fall into the LKC category for the living kind questions, and to fall into the AC category for artifact questions; in contrast, it would be reasonable to expect the children's justifications for no answers to be divided between the two categories regardless of question. In fact, for both 3- and 4-year-olds, this pattern seemed to hold (see Table 5).

Overall, the 4-year-olds were fairly good at justifying their answers. On 83% of the 4-year-olds' trials, responses fell into the LKC or AC category, on 10% of the trials responses fell into Other, and on 7% of the trials the subjects did not respond. Of the codable responses, 94% were correct.

To analyze the justification data, we started by separating the questions into four types: living kind/person-mend, living kind/ regrowth, artifact/person-mend, and artifact/ regrowth questions. For each child we then separated the yes responses and the no responses to each question type. We first examined only justifications for the yes responses, counting the number of LKC and AC justifications. For each question type, we then subtracted the number of AC responses from the number of LKC responses each child gave; thus, for each of the four questions each child was given a justification score between 4 (four LKC justifications/ zero AC justifications) and -4 (zero LKC justifications/four AC justifications). Wil- coxin rank sum tests were performed on the children's scores. The 4-year-olds gave more

LKC justifications than AC justifications on the living kind/regrowth questions, T+(15) = 120, p < .0001, and more AC justifications than LKC justifications on the artifact/person-mend questions, T+(14) = 117, p < .0001. There was no significant difference on the living kind/person-mend or the artifact/regrowth questions.2

The 4-year-olds' justifications for yes answers were then coded for consistency within each child. For each question type we placed the child in one of three categories: a child was considered to be an LKjus- tifier if the child had a score of 3 or 4 in the tabulation above, an ART justifier if the child had a score of -3 or -4, and Inconsis- tent if the child did not meet either criterion. Note that a child with a score of 3 or 4 gave only LKC justifications and a child with a score of -3 or -4 gave only AC justifications.3 Eleven of the 16 4-year-olds qualified as LK justifiers on the living kind/regrowth questions, and 11 of the 4-year-olds qualified as ART justifiers on the artifact/person-mend question. Two children qualified as LKjusti- fiers on the artifact/regrowth question (see Table 6).

It seems that when 4-year-olds justified their answers, they did so in an appropriate manner. Many of the 4-year-olds consistently used the characteristics of living kinds to justify the living kind/regrowth questions and used the characteristics of artifacts to justify the artifact/person-mend questions; this pattern suggests that at some level children realize that animals and plants share some properties and that these properties are different from those of artifacts.

Predictably, 3-year-olds were not as good at justifying their responses. Fifty- seven percent of their trials were coded into the LKC and AC categories, 36% of their trials received justifications coded into Other, and 11% of their trials received no response. Of the codable responses, 82% were correct. We repeated the above analyses for the 3- year-olds, first calculating the children's justification scores, again ranging from -4 to 4, for each question type. Considering only the yes responses, we then performed Wilcoxin rank sum tests on the children's scores. The

2 The results were the same when the yes and no responses were considered together. There were no significant differences when only no responses were considered.

3 A score of 3 could result only from a child's justifying three questions with living kinds justifications and offering no codable justifications for one question. If even one question was justified with an artifact justification, the maximum score would be 2 (3 LK - 1 ART justification). A similar analysis holds for a score of -3.

1252 Child Development TABLE 5

NUMBER OF EACH TYPE OF CORRECT JUSTIFICATIONS GIVEN BY CHILDREN: EXPERIMENT 2

AGE

3-Year-Olds 4-Year-Olds

ANSWER TYPE Living Artifact Living Artifact

Yes: Person-mend:

Living-kind characteristic .................. 8 1 3 0 Artifact characteristic ....................... 12 20 9 43 Total possible ......................... 38 40 20 50

Regrowth: Living-kind characteristic .................. 16 1 45 0 Artifact characteristic ............................. 4 10 0 3 Total possible ......................................... 39 23 55 7

No: Person-mend:

Living-kind characteristic ..................... 7 a 17 a Artifact characteristic ............................. 5 12 18 7 Total possible ..................................... 26 24 44 14

Regrowth: Living-kind characteristic ................... 1 7 0 26 Artifact characteristic .......................... 5 12 0 22 Total possible ........................................ 25 41 9 57

a It was not possible for a child to give a correct response in this cell.

3-year-olds gave significantly more AC justifications than LKC justifications on the artifact/person-mend questions, two-tailed T+(11) = 63.5, p < .01, and showed a trend to give more LKC justifications than AC justifications on the living kind/regrowth questions, two-tailed T+(9) = 37.5, p < .10. There were no significant differences on the living kind/person-mend and the artifact/regrowth questions.4 It seems 3-year-olds may know something about how people mend artifacts but may not have much understanding of principles of regrowth.

The 3-year-olds' justifications for yes answers were then coded for consistency within each child. Again, children were coded as LK, ART, or Inconsistent justifiers for each question type. Three of the 16 3- year-olds qualified as LKjustifiers on the living kind/regrowth questions, and two of the 3-year-olds qualified as ART justifiers on the artifact/person-mend question. No children qualified as LK or ART justifiers on the remaining questions (see Table 6). Overall, 3- year-olds seemed not to be consistent in the way they justified their answers, although a few showed some knowledge of what constitutes an appropriate justification.

Discussion Experiment 2 clearly shows that by 4

years children know that living kinds heal by themselves and that artifacts must be fixed through human intervention. As in Ex- periment 1, 4-year-olds responded similarly to plant and animal questions, differentiating them from artifacts. Four-year-olds explicitly mentioned growth as a mechanism of healing for plants and animals, showing knowledge of what kinds of things grow and what kinds of things do not. Moreover, 4- year-olds knew what kinds of remedies people can and cannot perform, and rarely attributed to people the ability to heal living kinds.

Three-year-olds, however, were only beginning to understand growth and human intervention. When asked whether a person can return an object to its original state, they responded differently for artifacts than for living kinds. Three-year-olds were more likely to say that a person can mend an artifact than to say that a person can mend a living kind and less likely to say that an artifact can regrow than to say a living kind can regrow. However, this living kind-artifact distinction is not fully formed; the relatively

4 When both yes and no responses were considered, or when only no responses were considered, there were no significant differences on any question.


TABLE 6 NUMBER CONSISTENT JUSTIFIERS FOR EACH TYPE OF QUESTION: EXPERIMENT 2

AGE

3-Year-Olds 4-Year-Olds

ANSWER TYPE LK Inconsistent ART LK Inconsistent ART

Living kind/regrowth........................... 3 13 0 11 5 0 Living kind/person-mend....................... 0 16 0 0 16 0 Artifact/regrowth .................................... 0 16 0 2 14 0 Artifact/person-mend ............................. 0 14 2 0 5 11

high error rate (18%) in justifications, the number of "other" justifications, and the number of nonresponses suggest that 3-year- olds are less knowledgeable about plants and animals, and about the limitations or abilities of people, than are 4-year-olds. Al- though 3-year-olds know that in general artifacts do not fix themselves, most of their knowledge about healing and mending seems to concern the methods people use to mend things and the limitations of these methods ("It won't stick"). Three-year-olds seemed to know much less about the mechanisms that affect living kinds.

Experiment 3 Experiments 1 and 2 investigated only

familiar living kinds and artifacts; thus children may have answered the questions based on experience with these specific items and transformations. For example, children may have said that a rosebush can grow another rose because they have seen this happen and said that a person cannot put the rose back on the rosebush because they realize it is not generally tried. Hence, the question remains whether children are answering correctly on the basis of memory or specific experience, or whether they possess more general knowledge that will help them build and use a biological theory (see Massey & Gelman, 1988). In the following experiment, unfamiliar animals, plants, and artifacts were added in order to assess whether there is a general basis to 4-year- olds' knowledge. If children respond correctly to questions about unfamiliar plants, animals, and artifacts, they show evidence of general knowledge about the types of transformations these kinds undergo. We also included living-kind replicas (e.g., a coin- operated horse, fake flowers); in order to

treat these as artifacts children must ignore salient clues such as the shape of the parts, size, and overall shape, instead using subtle information such as texture, shininess, and rigidity as a basis of their decisions. Method

Subjects.--Eighteen 4-year-olds (M = 4-9, range = 3-11 to 5-3, 9 males, 9 females) recruited from a university preschool participated in the main experiment. The children represented a racially mixed but predomi- nately Caucasian middle-class population. Four additional children were dropped, two who failed to complete the procedure and two who exhibited a response bias. Ten additional 4-year-olds participated in a preliminary ratings task.

Materials.-Each subject was asked about the repair of 24 items. The stimulus set consisted of 4-inch x 6-inch photo- graphs. The eight items from Experiments 1 and 2 were included, with the exception of a thicket of daisies replacing the rosebush.5 In addition, we included four unfamiliar animals, four unfamiliar plants, four replicas of animals and plants (two each), and four unfamiliar artifacts. Items were pictured untrans- formed. The unfamiliarity of the items was established through ratings by a different group of 10 4-year-olds. Children were able to name unfamiliar animals and plants with an appropriate superordinate term (animal, plant, bird); however, at least 9 of 10 children failed to produce basic-level names. Similarly, except for the robot, all children were unable to name the unfamiliar artifacts. A list of the unfamiliar items and living-kind replicas is given in Table 7.

Procedure.-With the exception of the wording of the questions, the procedure was identical to that of Experiment 1. The object

5 We could not find a photograph of a rosebush with fine enough resolution to differentiate it from human-made roses.

1254 Child Development TABLE 7

ADDITIONAL ITEMS USED IN EXPERIMENT 3

Item Part Cut Off

Unfamiliar animals: Sloth ............................................. H air Ferret............................... Fur Turkey ........................................ Feather Fish (lionfish) ............................... Scale

Unfamiliar plants: Palm .................. ...................... Cone Fern ........................................ Leaf Flower (lupine) .......................... Bud Cactus ...................................... Spine

Living-kind replicas: Rabbit model .............................. Tail Coin-operated horse ................... Mane Fake tree (for fish tank) ............... Branch Plastic funeral wreath .................. Rose

Unfamiliar artifacts: Power sander ........................... Cord Power washer ............................. Nozzle Overhead projector .................... Arm Robot ..................................... Resistor

was never named, as we felt that many unfamiliar names might prove overwhelming for the children, and familiar names (e.g., plant) might encourage the children to use memo- rized knowledge. Therefore, in this experiment, children were told, "See this? Some- body cut the y off of it." For most items, the regrowth question was then, "Do you think the y could get long by itself?" The person- mend question was, "Do you think a person could make the y long?" For the daisy thicket, shirt, funeral wreath, lionfish, fern, and lupine, the regrowth question was, "Do you think this could get another y by itself?" and the person-mend question was, "Do you think a person could get this another y?" For all of the questions, the experimenter pointed to the part mentioned in the question. Because of the number of items used, children were not asked for justifications. Results

The analyses follow the same pattern as those of Experiments 1 and 2. We first examined whether children treat the familiar plants and animals items similarly. Because there were no differences in the way children treat familiar plants and animals, we combined them in the subsequent analyses, both at the group and at the individual level. We left comparison of the unfamiliar plants and unfamiliar animals to the overall analysis; because the children's scores for these kinds ranged from 0 to 4, we were able to analyze them in the main ANOVA.

Familiar plants versus animals.-To see whether children responded differently to familiar plants and animals, we assigned them scores representing the number of yeses (0-2) they gave to the person-mend question and to the regrowth question, first for the animal items and then for the plant items. Children were coded as positive if they received a higher score for animals than plants, and negative if they received a higher score for plants than animals. McNemar tests indicated that there was a trend for children to score higher on the familiar plant items than the familiar animal items for the person-mend question, X2(1) = 2.50, p's < .10, but there was no significant difference between the plants and the animals for the regrowth question, X2(1) < 1.45, p > .10. Thus, we grouped the familiar plants and animals together as familiar living kinds.

Living kinds versus artifacts.-We next conducted a 6 (kind: familiar living kind, familiar artifact, unfamiliar animal, unfamiliar plant, living-kind replicas, unfamiliar artifact) x 2 (agent: person-mend vs. regrowth) repeated-measures ANOVA in order to see how children responded to different item types on the regrowth and person- mend questions. The ANOVA yielded a significant kind x agent interaction, F(5, 85) = 23.56, p < .001, and a significant main effect of kind, F(5, 85) = 6.05, p < .001. Simple effects analyses showed a significant effect of agent for all kinds except the living-kind replicas. Children were significantly more likely to respond that the familiar living kinds, unfamiliar animals, and unfamiliar plants could regrow than that a person could mend them, F's(1, 17) > 16.20, p's < .001. Similarly, children were more likely to respond that a person could mend familiar and unfamiliar artifacts than that they could regrow, F's(1, 17) > 9.8, p's < .01. A complete list of means is given in Table 8. For the regrowth question, the means for the familiar and unfamiliar artifacts were below chance, t's(17) > 5.53, p's < .001, for the person-mend question, the unfamiliar animals, unfamiliar plants, and living-kind replicas were below chance, t's(17) > 4.27, p's < .005. No other means were significantly different from chance.

Tukey HSD tests were then conducted to determine whether children treated the various living-kind and artifact categories similarly. There were no significant differences between the familiar living kinds, unfamiliar animals, or unfamiliar plants for the

Backscheider, Shatz, and Gelman 1255 TABLE 8

PERCENT OF POSITIVE RESPONSES TO EACH QUESTION TYPE OF EXPERIMENT 3

QUESTION

ITEM TYPE Person-mend Regrowth

Familiar living kinds ............... 25* (.19) 64 (.31) Unfamiliar animals.................. 7* (.12) 50 (.39) Unfamiliar plants ..................... 18* (.19) 56 (.34) Familiar artifacts ..................... 58 (.33) 11* (.13) Unfamiliar artifacts .................. 33 (.38) 4* (.10) Living-kind replicas................. 26* (.23) 36 (.28)

NOTE.-Standard deviations are given in parentheses. * p < .001, different from chance by two-tailed t test.

person-mend or regrowth question (p's > .05). In addition, there were no significant differences between the familiar and unfamiliar artifacts on either question. The children's responses to the living-kind replica items were not systematically similar to the other living-kind or artifact categories.

We next asked whether individual children answered the questions consistently. A binomial test (where p < .05) of whether the yes/no responses to the person-mend and regrowth questions were above chance required at least 13 of 18 children to get three or four out of four items in each category correct. For all three living-kind categories, familiar living kinds, unfamiliar animals, and unfamiliar plants, children performed above chance on the person-mend questions, with 13, 18, and 15 children scoring at least three out of four correct, respectively. Thus, children tended to reply that human beings cannot fix living kinds. For the regrowth questions, the children scored above chance on both familiar and unfamiliar artifacts: every child scored at least three out of four correct for both types of artifacts. Thus, children seem to know that artifacts do not regrow. Discussion

In Experiment 3, even with unfamiliar items 4-year-olds showed they realize that people do not fix living kinds and that artifacts do not regrow. Children differentiated between artifacts and living kinds whether they were familiar or unfamiliar, although they still made significant errors when asked whether a living kind could regrow or whether a person could mend an artifact. For the living-kind replicas children did not significantly distinguish the person-mend and regrowth questions. Children may have been unsure of whether we meant to refer

to the replicas themselves or to the living kinds they symbolized. Children did not treat these items like the other artifacts or like the other living kinds. Exactly what children believe to be true of these replicas is an issue for future study.

Unlike our previous findings, children scored at chance when asked if living kinds regrow and if people can fix artifacts. This result demonstrates that children found the procedure, including unfamiliar kinds, more difficult. Their ability to answer above chance on the unfamiliar items suggests that children have some general knowledge, but their better performance on the familiar items suggests that specific knowledge is also important. In sum, Experiment 3 suggests that 4-year-olds know that artifacts, both familiar and unfamiliar, do not regrow and that plants and animals, both familiar and unfamiliar, are not fixed by people.

General Discussion Overall, 3- and 4-year-olds realize that

plants and animals heal through regrowth and that this ability separates artifacts from both plants and animals. Because previous studies (Carey, 1985; Richards & Siegler, 1986) found little evidence suggesting that children are able to group plants and animals together, this new result is surprising. Moreover, although it is not clear that children are explicitly aware that, as a category, living things grow and heal while artifacts do not, children make just this distinction in their responses and justifications about regrowth. Apparently, plants and animals can be treated alike if the task so warrants.

The questions we asked the children were at times rather awkward (e.g., "Could the leg [cut off the table] get long by itself?").

1256 Child Development However, even though we used these awkward constructions, children were able to perform well and differentiate living kinds from artifacts. In constructing these questions we realized that the English language has no neutral way of talking about healing and mending. Language itself may carry information about distinctions, such as the living kind-artifact distinction, to the child.

This research extends Rosengren et al.'s (1991) finding that children are aware of some of the characteristics of growth, as well as the work on children's awareness of biological cause (Gelman, 1988; Springer & Keil, 1991). Apparently, preschool children are noticing a variety of living-kind characteristics such as growth, regrowth, the independence from intentional intervention, and dependence on biological cause. Thus, 4- year-olds seem to be building a coherent biological understanding. It is possible that children first separate living kinds from artifacts through growth and independence from external human intervention. Of course, the variables affecting growth in one living kind are often different from those affecting growth in another; plant growth dif- fers from animal growth on several dimen- sions (Hickling & Gelman, 1992). It is not clear from the present studies the extent to which children realize the similarities and differences between plant and animal regrowth. Children may simply realize that plants and animals heal by themselves and that people mend artifacts. Moreover, when other cues, like movement, are made salient, children may not be able to isolate characteristics like regrowth that bind living kinds. It would be interesting to see how the same children responded in more than one task setting that made different kinds of characteristics salient.

In the preschool and elementary school years, children learn a great many distinctions: among them, the living kind-artifact distinction, the living-nonliving distinction, the animate-inanimate distinction, and the animal-plant distinction. Some of these distinctions recruit hierarchically organized categories; for example, there is a hierarchi- cal relation between the superordinate category, living things, and the subordinate categories, plants and animals. Some of 'the distinctions to be learned cut across hierar- chical organizations, however. For example, plants and animals are living kinds, whereas artifacts are nonliving, but both plants and artifacts are inanimate, whereas animals are animate. Children must eventually learn

how these distinctions are organized with respect to one another. In acquiring this knowledge, they may learn characteristics intrinsic to the distinctions (e.g., living kinds grow and are affected by biological mechanisms) before they fully understand the structural relations among the distinctions. Whether preschoolers are able to move among the structures is still an unanswered question; they may not explicitly realize that a tree is inanimate like a chair but, at the same time, living like a horse.

In sum, 4-year-old children can group living kinds together, if only implicitly. Even 3-year-olds show some beginning ability to do so. To some extent, then, Carey's (1985) caution that children may have a concept of living kinds but simply may not map the word "alive" to it appears justified. Our findings indicate that preschool children can implicitly group living kinds together when asked about regrowth and mending, showing through their responses and justifications the beginnings of a theory of biology applicable to the domain of living kinds.

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