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Lay understanding of mendelian genetics
Lav understanding of mendelian genetics d
Over the past decade there have been growing calls for more public education in genetics. For example, the UK House of Commons Science and Technology Committee) in a report in 1995 suggests that better understanding is necessary for appropriate use of genetic tests and other new techniques and would lead to a more public involvement in debates on the ethics and the deployment of new genetic technologies. Others argue for a public ‘genetic literacy’ simply because genetics is now such an important part of our culture. In Britain, there has been some response to these calls including a growing represenof genetics in the National tation Curriculum for schools and activities such as the plays and exhibitions with genetic themes which have been sponsored by the Wellcome Trust. However, despite these developments, and indeed wider efforts to popularize mendelian genetics throughout the century. public understanding of mendelian genetics is very limited as has been repeatedly demonstrated in studies of school children and young peoplez4, those who have attended genetic counselling, where an explanation of the relevant genetics is generally given7,8, and the public at large. While we may sometimes gain the opposite impression because terms such as gene and DNA are now so widely used by the public, we need to be careful to note that these terms may be used in very different ways inside and outside the scientific world. When I recently heard a 1O-year-old say that another boy at his school had the ‘aggression gene’, I assume that he meant that this boy was often aggressive, or perhaps that he had an aggressive character, rather than making any statement about molecular genetics. A study of nearly 150 couples who were carriers of a recessively inherited single gene disorder who in almost all cases had a child with the disorder and had received genetic counselling demonstrated some of the difficultiess. While a reassuringly high proportion (95%) were able to state the correct chance of having an affected child, only 36% correctly identified the probabilities of this, having a child who is a carrier and one who is a non-carrier. It is reasonable to conclude therefore that a majority of these couples failed to understand the basic principle of recessive inheritance. So, outside scientific circles, the mendelian account of inheritance has not become widely accepted or understood nor does it provide the usual framework in which inheritance is discussed. Why should this be? The basic principles of the behaviour of the chromosomes at cell division, the formation of the gametes and at fertilization are not particularly difficult to understand. But what the studies show is that what is often missing in lay understanding is any
Copyright
0 1998 Elsevier
Science
Ltd. All right resewed.
concept of what in scientific terms we would call the phenotype and genotype. There is no concept of a genetic material which is transferred across generations to play a vital role in the development of the new individual. The usual response to evidence of poor understanding of the scientific concepts is to blame the teacher. Clearly, it is often said, the explanation must have been inadequate. While it is certainly true that some school teachers themselves feel poorly prepared and unconfident in teaching genetics, not all do. And, particularly in the face of many excellent popular accounts in books and in the media, I find this traditional explanation of poor public understanding unconvincing. What is striking about the way genetics is usually taught is that the teaching assumes that a pupil knows nothing about inheritance before the lesson begins. However, we know this is false. Even preschool children have been shown to understand a basic premise of inheritance that family members, as opposed to close friends for instance, are likely to share particular physical characteristics9,to. Young children also generally know where babies come from and that cats have kittens and dogs have puppiesit. Indeed, for adults as well as children, there is a very rich lay knowledge, and indeed interest in, inheritance as may be heard in almost any family discussion of a newborn baby usually with speculation of who he or she takes after. It may be that mendelian explanations of inheritance are poorly accepted and understood because they conflict in a number of ways with a widespread and well grounded lay understanding of inheritance which is derived from the social relationships of kin~hip~~,)3.We do not find the mendelian concept easy because it does not fit with what we already know. We are likely to resemble those who are closest to us in kin terms, which in English kinship will mean our parents and our children. Because lay notions of inheritance are grounded in concepts of kinship and because these kinship relations are constantly reinforced by everyday social practice and relationship, they may be particularly resistant to change. Thus, learning mendelian genetics is not a matter of assimilating something new, but of replacing some well established and intuitive ideas which are constantly reinforced by what we see around ourselves with others that are not all self evident. Lay knowledge of inheritance Knowledge of the inheritance of family characteristics is a fundamental part of family culture in Western societies. Such knowledge includes patterns of inheritance in families of physical features, of aspects of behaviour, character, personality, mannerisms and personal habits as well as
0160-9327/96/$19.00.
PII. SO160-9327(98)01125-9
health and proneness to illness’J-‘h. Discussions of family photographs, for example, often centre around who ‘takes after’ whom. Different features may be linked to different family members. ‘He has got his father’s eyes but his mother’s hair’. Or a feature may be seen to have come from one side of the family or the other. The general view seems to be that, potentially at least, there is an equal contribution of characteristics from each side of the family. Though an exception to this is that particularly male or female characteristics are usually assumed to have been inherited from the same sex parent. This latter point may lead to complications in genetic counselling in families that carry the inherited form of breast and ovarian cancer. It may be very hard for family members to understand that the gene mutation can be transmitted via males in the familyt7. In some families, a particular characteristic may be seen as ‘strong’ or ‘dominant’, meaning that it is likely to persist across generations and dominate over characteristics that might otherwise be inherited from the other side of the family. Many families that carry inherited disorders, especially those which are dominantly inherited (in the mendelian sense) are all too well aware that the disorder ‘runs in their family’ without need of a genetic counsellor to point this out to them17.18. The irregular appearance of a condition with less than complete penetrance (such as the BRCAI and BRCA2 mutations that are linked to breast and ovarian cancer) is often explained by the loose application of a notion of a principle of a characteristic ‘skipping a generation’ or, for instance. that the disease is likely to strike a first born daughter or those who adopt a particular lifestyle. The occurrence of the disease is frequently linked to other (phenotypic) characteristics, so that, for instance, a niece who ‘takes after’ an aunt in facial appearance or character may be seen very likely to get the cancer that the aunt suffered or, conversely, because she is so unlike her in various ways, she will be free of the disease. Often in these families an external ‘trigger’ is seen to be required to make manifest the latent cancer - a fall in which the breast was bruised, for instance, may be cited as the reason for the development of the tumour. Like Darwin’s view of inheritance. in lay theories of inheritance acquired characters may be passed on. Just as Darwin believed that repeated male circumcision across the generations would lead to changes in the structure of the foreskin, so many young school children believe that mice whose tails have been cut off will give rise to tailless descendant&r*. Consider this account from a member of family who carried an inherited cancer syndrome:
Endeavour
Vol. 22(3)
1998
93
If you had to flush out a bad gene, or a bad chemical or something, I think it must take a great deal getting rid of for absolutely every single bit of it to go, yes, several generations, for it to go. That means several generations of people taking particular precautions in the knowledge of what they’re doing to get rid of it. So I suppose I imagine it’s - little bits of it hang on and therefore if somebody is particularly stressed.. .I would imagine that aggravates that. In many explanations it is very unclear what is passed between generations. Some say that it is ‘in the blood’, an explanation consistent with notions of blending inheritance and clearly intuitively more appealing to many people than Mendel’s particulate ‘atomic’ theory. But while in many lay discussions of inheritance there are notions of blood, blood lines, etc. most informants do not seem to imply that in a literal sense blood is the hereditary substance. If pressed on this point in interviews people often mention sexual intercourse but usually do not name a specific genetic substance nor imply there is a specific substance that is transmitted at conception. So while we may know where babies come from we are not always entirely sure how they get there. In short, we may characterize many lay accounts of inheritance, in contrast to mendelian explanations, by their lack of a clear distinction of phenotype and genotype characterization of the genetic material, or an idea of the segregation of inherited characters. Lay explanations may also include the transmission of acquired characters and influences. The English (and North American and other societies derived from Western European peoples) the kinship system is bilateral and has a strong emphasis on descentig-2’. So more or less equal roles are given to the two sides of the family. We do not, for example, have specific terms to distinguish maternal and paternal aunts, uncles or grandparents as many other societies do. With the exception of characteristics typical of one or other sex, lay notions of inheritance seem to give equal weight to the two sides of the family and so are parallel to the kinship system. Our emphasis on descent may be seen in our usual pattern of the inheritance of goods and property which are passed from parents to children. Social and legal obligations follow the same vertical pattern linking parents and children much more strongly than lateral links between, say, brothers and sisters. Grandparents are part of the same descent system and, for instance, this is articulated in the legal system which acknowledges their connection with their grandchildren in ways that are not true, for instance, for uncles and aunts and nephews and nieces. If lay ideas about inherited or genetic connections are derived from notion of kinship, a testable prediction can be derived from these features of our kinship system by using a situation where there is a divergence between the genetic
94
Endeavour Vol. 22(3) 1998
connection and strength of the kin tie. In English kinship this is provided by a comparison of the perceived genetic connection between parents and children and that between siblings. Here we would predict that parents and children would be seen as closer in genetic terms than siblings. This prediction was tested as part of a postal questionnaire sent to two samples of women and a mixed group of university studentsl3. The question asked was ‘What proportion of genes does someone, on average, share with their father, sister, child, uncle and grandmother?’ The possible response options were, none, 5%, 15%, 25%, 50%, 75%, 100% or don’t know. For father and child, the majority chose the correct response and there was no particular tendency to over or under estimate. For the other categories of kin, fewer got the answer right and there were a strong bias towards under estimation. It might be suggested that the pattern of results could be explained by the fact that while the proportion of genes (alleles) transmitted from each parent to a child is fixed, there is individual variability in the case of lateral kin and grandparents. While this might lead to more uncertainty about the connections with these kin, it does not explain why there should be a systematic under estimation with these kin. Even with father and child there were a significant number of respondents who do not know that parents contribute an equal proportion of genes to their children.
Acknowledgements I acknowledge support for some of the research on which this paper draws from the Medical Research Council and the Nuffield Foundation and the contributions of other members of the Centre for Family Research to this research. Martin P.M. Richards
Centre for Family Research, of Cambridge, UK.
References 1
House
of
Technology
6
7 8
9
Implications for education If the hypothesis that lay knowledge of inheritance is derived from notions of kin relationships and that this lay knowledge impedes the assimilation of a mendelian account is correct, there are profound implications for education in schools, in clinics and more generally. It supports the view that science education must be ‘bottom up’ rather than ‘top down’ and that it should not begin with the assumption that people know nothing and simply require a straightforward explanation in simplified terms of the scientific view. Rather, teaching should begin from an understanding of the pre-existing knowledge that an individual may bring to a learning situation and focus on the conflicts between this and the mendelian explanationQ23. Top-down accounts which ignore the prior lay knowledge are unlikely to be successful in achieving a widespread scientific understanding. Traditionally such approaches to science education have predominated and they are still more or less universal in the teaching of genetics in schools. While I think we need to understand much more about the interrelationship of the lay knowledge of kinship and inheritance which children bring to schools and the teaching of genetics they receive there, I think the evidence of failure to create a widespread public understanding of genetics already gives sufficient grounds to critically reassess the teaching of genetics in schools.
University
10 11 12 13 14 15
16 17 18 19 20 21
22
23
Commons Committee
Science and (1995) Third
Report Human Genetics: the Science and its Consequences, Vol. I, HMSO Kargbo, D.B., Hobbs, E.D. and Erickson, G.L. (1980) J. Biol. Educ. 14, 137-146 Longden, B. (1982) J. Biol. Educ. 16, 135-140 Clough, E.E. and Wood-Robinson, C. (1985) J. Biol. Educ. 24, 29-47 Wood-Robinson, C. et al. (1996) Young Peoples Understanding of ‘The New Genetics’. Learning in Science Research Group, University of Leeds Working Paper No. 1 Lewis, J. et al. (1997) Understanding of Basic Genetics and DNA Technology, Learning in Science Research Group, University of Leeds. Working Paper 2 Kessler, S. (1989) Am. J. Med. Genet. 34, 34ck353 Snowdon, C. and Green, J.M. (1994) Unpublished Report, Centre for Family Research, University of Cambridge Carey, S. and Spelke, E. (1994) in DomainSpecific Knowledge and Conceptual Change (Hirschfeld, L.A. and Gelman, S.A., eds), pp. 160-200, Cambridge University Press Springer, K. (1992) Child Dev. 63, 950-959 Johnson, S.C. and Soloman, G.E.A. (1997) Child Dev. 68,404--119 Richards, M.P.M. (1996) Public Understand. Sci. 5, 217-230 Richards, M.P.M. and Ponder, M. (1996) J. Med. Genet. 33, 1032-1036 Davison, C., Frankel, S. and Smith, G.D. (1989) Health Educ. Res. 4,329-340 Richards, M.P.M. (1996) in The Troubled Psychological Helix: Social and Implications of the New Human Genetics (Marteau, T. and Richards, M.P.M., eds), pp. 249-273, Cambridge University Press Ponder, M. et al. (1996) J. Med. Genet. 33, 4855492 Richards, M.P.M. et al. (1995) Genet. Counsel. 4,219-233 Green, J., Murton, F. and Statham, H. (1993) J. Med. Genet. 30, 101-105 Scheinder, D.M. (1968) American Kinship: a Cultural Account, Prentice Hall Craig, D. (1979) Am. Anthropol. 8 1,94-95 Strathem, M. (1992) After Nature: English Kinship in the Late Twentieth Century, Cambridge University Press Layton, D. et al. (1993) Inarticulate Science? Perspectives on the Public Understanding of Science and Some Implications for Science Education, Driffield Yorks: Studies in Education Ltd. Wood-Robinson, C. (1994) in Learning Science in Schools. Research Reforming Practice (Glynn, S. and Duit, R., eds), pp. 11 l-130, AAAS
Over the past decade there have been growing calls for more public education in genetics. For example, the UK House of Commons Science and Technology Committee) in a report in 1995 suggests that better understanding is necessary for appropriate use of genetic tests and other new techniques and would lead to a more public involvement in debates on the ethics and the deployment of new genetic technologies. Others argue for a public ‘genetic literacy’ simply because genetics is now such an important part of our culture. In Britain, there has been some response to these calls including a growing represenof genetics in the National tation Curriculum for schools and activities such as the plays and exhibitions with genetic themes which have been sponsored by the Wellcome Trust. However, despite these developments, and indeed wider efforts to popularize mendelian genetics throughout the century. public understanding of mendelian genetics is very limited as has been repeatedly demonstrated in studies of school children and young peoplez4, those who have attended genetic counselling, where an explanation of the relevant genetics is generally given7,8, and the public at large. While we may sometimes gain the opposite impression because terms such as gene and DNA are now so widely used by the public, we need to be careful to note that these terms may be used in very different ways inside and outside the scientific world. When I recently heard a 1O-year-old say that another boy at his school had the ‘aggression gene’, I assume that he meant that this boy was often aggressive, or perhaps that he had an aggressive character, rather than making any statement about molecular genetics. A study of nearly 150 couples who were carriers of a recessively inherited single gene disorder who in almost all cases had a child with the disorder and had received genetic counselling demonstrated some of the difficultiess. While a reassuringly high proportion (95%) were able to state the correct chance of having an affected child, only 36% correctly identified the probabilities of this, having a child who is a carrier and one who is a non-carrier. It is reasonable to conclude therefore that a majority of these couples failed to understand the basic principle of recessive inheritance. So, outside scientific circles, the mendelian account of inheritance has not become widely accepted or understood nor does it provide the usual framework in which inheritance is discussed. Why should this be? The basic principles of the behaviour of the chromosomes at cell division, the formation of the gametes and at fertilization are not particularly difficult to understand. But what the studies show is that what is often missing in lay understanding is any
Copyright
0 1998 Elsevier
Science
Ltd. All right resewed.
concept of what in scientific terms we would call the phenotype and genotype. There is no concept of a genetic material which is transferred across generations to play a vital role in the development of the new individual. The usual response to evidence of poor understanding of the scientific concepts is to blame the teacher. Clearly, it is often said, the explanation must have been inadequate. While it is certainly true that some school teachers themselves feel poorly prepared and unconfident in teaching genetics, not all do. And, particularly in the face of many excellent popular accounts in books and in the media, I find this traditional explanation of poor public understanding unconvincing. What is striking about the way genetics is usually taught is that the teaching assumes that a pupil knows nothing about inheritance before the lesson begins. However, we know this is false. Even preschool children have been shown to understand a basic premise of inheritance that family members, as opposed to close friends for instance, are likely to share particular physical characteristics9,to. Young children also generally know where babies come from and that cats have kittens and dogs have puppiesit. Indeed, for adults as well as children, there is a very rich lay knowledge, and indeed interest in, inheritance as may be heard in almost any family discussion of a newborn baby usually with speculation of who he or she takes after. It may be that mendelian explanations of inheritance are poorly accepted and understood because they conflict in a number of ways with a widespread and well grounded lay understanding of inheritance which is derived from the social relationships of kin~hip~~,)3.We do not find the mendelian concept easy because it does not fit with what we already know. We are likely to resemble those who are closest to us in kin terms, which in English kinship will mean our parents and our children. Because lay notions of inheritance are grounded in concepts of kinship and because these kinship relations are constantly reinforced by everyday social practice and relationship, they may be particularly resistant to change. Thus, learning mendelian genetics is not a matter of assimilating something new, but of replacing some well established and intuitive ideas which are constantly reinforced by what we see around ourselves with others that are not all self evident. Lay knowledge of inheritance Knowledge of the inheritance of family characteristics is a fundamental part of family culture in Western societies. Such knowledge includes patterns of inheritance in families of physical features, of aspects of behaviour, character, personality, mannerisms and personal habits as well as
0160-9327/96/$19.00.
PII. SO160-9327(98)01125-9
health and proneness to illness’J-‘h. Discussions of family photographs, for example, often centre around who ‘takes after’ whom. Different features may be linked to different family members. ‘He has got his father’s eyes but his mother’s hair’. Or a feature may be seen to have come from one side of the family or the other. The general view seems to be that, potentially at least, there is an equal contribution of characteristics from each side of the family. Though an exception to this is that particularly male or female characteristics are usually assumed to have been inherited from the same sex parent. This latter point may lead to complications in genetic counselling in families that carry the inherited form of breast and ovarian cancer. It may be very hard for family members to understand that the gene mutation can be transmitted via males in the familyt7. In some families, a particular characteristic may be seen as ‘strong’ or ‘dominant’, meaning that it is likely to persist across generations and dominate over characteristics that might otherwise be inherited from the other side of the family. Many families that carry inherited disorders, especially those which are dominantly inherited (in the mendelian sense) are all too well aware that the disorder ‘runs in their family’ without need of a genetic counsellor to point this out to them17.18. The irregular appearance of a condition with less than complete penetrance (such as the BRCAI and BRCA2 mutations that are linked to breast and ovarian cancer) is often explained by the loose application of a notion of a principle of a characteristic ‘skipping a generation’ or, for instance. that the disease is likely to strike a first born daughter or those who adopt a particular lifestyle. The occurrence of the disease is frequently linked to other (phenotypic) characteristics, so that, for instance, a niece who ‘takes after’ an aunt in facial appearance or character may be seen very likely to get the cancer that the aunt suffered or, conversely, because she is so unlike her in various ways, she will be free of the disease. Often in these families an external ‘trigger’ is seen to be required to make manifest the latent cancer - a fall in which the breast was bruised, for instance, may be cited as the reason for the development of the tumour. Like Darwin’s view of inheritance. in lay theories of inheritance acquired characters may be passed on. Just as Darwin believed that repeated male circumcision across the generations would lead to changes in the structure of the foreskin, so many young school children believe that mice whose tails have been cut off will give rise to tailless descendant&r*. Consider this account from a member of family who carried an inherited cancer syndrome:
Endeavour
Vol. 22(3)
1998
93
If you had to flush out a bad gene, or a bad chemical or something, I think it must take a great deal getting rid of for absolutely every single bit of it to go, yes, several generations, for it to go. That means several generations of people taking particular precautions in the knowledge of what they’re doing to get rid of it. So I suppose I imagine it’s - little bits of it hang on and therefore if somebody is particularly stressed.. .I would imagine that aggravates that. In many explanations it is very unclear what is passed between generations. Some say that it is ‘in the blood’, an explanation consistent with notions of blending inheritance and clearly intuitively more appealing to many people than Mendel’s particulate ‘atomic’ theory. But while in many lay discussions of inheritance there are notions of blood, blood lines, etc. most informants do not seem to imply that in a literal sense blood is the hereditary substance. If pressed on this point in interviews people often mention sexual intercourse but usually do not name a specific genetic substance nor imply there is a specific substance that is transmitted at conception. So while we may know where babies come from we are not always entirely sure how they get there. In short, we may characterize many lay accounts of inheritance, in contrast to mendelian explanations, by their lack of a clear distinction of phenotype and genotype characterization of the genetic material, or an idea of the segregation of inherited characters. Lay explanations may also include the transmission of acquired characters and influences. The English (and North American and other societies derived from Western European peoples) the kinship system is bilateral and has a strong emphasis on descentig-2’. So more or less equal roles are given to the two sides of the family. We do not, for example, have specific terms to distinguish maternal and paternal aunts, uncles or grandparents as many other societies do. With the exception of characteristics typical of one or other sex, lay notions of inheritance seem to give equal weight to the two sides of the family and so are parallel to the kinship system. Our emphasis on descent may be seen in our usual pattern of the inheritance of goods and property which are passed from parents to children. Social and legal obligations follow the same vertical pattern linking parents and children much more strongly than lateral links between, say, brothers and sisters. Grandparents are part of the same descent system and, for instance, this is articulated in the legal system which acknowledges their connection with their grandchildren in ways that are not true, for instance, for uncles and aunts and nephews and nieces. If lay ideas about inherited or genetic connections are derived from notion of kinship, a testable prediction can be derived from these features of our kinship system by using a situation where there is a divergence between the genetic
94
Endeavour Vol. 22(3) 1998
connection and strength of the kin tie. In English kinship this is provided by a comparison of the perceived genetic connection between parents and children and that between siblings. Here we would predict that parents and children would be seen as closer in genetic terms than siblings. This prediction was tested as part of a postal questionnaire sent to two samples of women and a mixed group of university studentsl3. The question asked was ‘What proportion of genes does someone, on average, share with their father, sister, child, uncle and grandmother?’ The possible response options were, none, 5%, 15%, 25%, 50%, 75%, 100% or don’t know. For father and child, the majority chose the correct response and there was no particular tendency to over or under estimate. For the other categories of kin, fewer got the answer right and there were a strong bias towards under estimation. It might be suggested that the pattern of results could be explained by the fact that while the proportion of genes (alleles) transmitted from each parent to a child is fixed, there is individual variability in the case of lateral kin and grandparents. While this might lead to more uncertainty about the connections with these kin, it does not explain why there should be a systematic under estimation with these kin. Even with father and child there were a significant number of respondents who do not know that parents contribute an equal proportion of genes to their children.
Acknowledgements I acknowledge support for some of the research on which this paper draws from the Medical Research Council and the Nuffield Foundation and the contributions of other members of the Centre for Family Research to this research. Martin P.M. Richards
Centre for Family Research, of Cambridge, UK.
References 1
House
of
Technology
6
7 8
9
Implications for education If the hypothesis that lay knowledge of inheritance is derived from notions of kin relationships and that this lay knowledge impedes the assimilation of a mendelian account is correct, there are profound implications for education in schools, in clinics and more generally. It supports the view that science education must be ‘bottom up’ rather than ‘top down’ and that it should not begin with the assumption that people know nothing and simply require a straightforward explanation in simplified terms of the scientific view. Rather, teaching should begin from an understanding of the pre-existing knowledge that an individual may bring to a learning situation and focus on the conflicts between this and the mendelian explanationQ23. Top-down accounts which ignore the prior lay knowledge are unlikely to be successful in achieving a widespread scientific understanding. Traditionally such approaches to science education have predominated and they are still more or less universal in the teaching of genetics in schools. While I think we need to understand much more about the interrelationship of the lay knowledge of kinship and inheritance which children bring to schools and the teaching of genetics they receive there, I think the evidence of failure to create a widespread public understanding of genetics already gives sufficient grounds to critically reassess the teaching of genetics in schools.
University
10 11 12 13 14 15
16 17 18 19 20 21
22
23
Commons Committee
Science and (1995) Third
Report Human Genetics: the Science and its Consequences, Vol. I, HMSO Kargbo, D.B., Hobbs, E.D. and Erickson, G.L. (1980) J. Biol. Educ. 14, 137-146 Longden, B. (1982) J. Biol. Educ. 16, 135-140 Clough, E.E. and Wood-Robinson, C. (1985) J. Biol. Educ. 24, 29-47 Wood-Robinson, C. et al. (1996) Young Peoples Understanding of ‘The New Genetics’. Learning in Science Research Group, University of Leeds Working Paper No. 1 Lewis, J. et al. (1997) Understanding of Basic Genetics and DNA Technology, Learning in Science Research Group, University of Leeds. Working Paper 2 Kessler, S. (1989) Am. J. Med. Genet. 34, 34ck353 Snowdon, C. and Green, J.M. (1994) Unpublished Report, Centre for Family Research, University of Cambridge Carey, S. and Spelke, E. (1994) in DomainSpecific Knowledge and Conceptual Change (Hirschfeld, L.A. and Gelman, S.A., eds), pp. 160-200, Cambridge University Press Springer, K. (1992) Child Dev. 63, 950-959 Johnson, S.C. and Soloman, G.E.A. (1997) Child Dev. 68,404--119 Richards, M.P.M. (1996) Public Understand. Sci. 5, 217-230 Richards, M.P.M. and Ponder, M. (1996) J. Med. Genet. 33, 1032-1036 Davison, C., Frankel, S. and Smith, G.D. (1989) Health Educ. Res. 4,329-340 Richards, M.P.M. (1996) in The Troubled Psychological Helix: Social and Implications of the New Human Genetics (Marteau, T. and Richards, M.P.M., eds), pp. 249-273, Cambridge University Press Ponder, M. et al. (1996) J. Med. Genet. 33, 4855492 Richards, M.P.M. et al. (1995) Genet. Counsel. 4,219-233 Green, J., Murton, F. and Statham, H. (1993) J. Med. Genet. 30, 101-105 Scheinder, D.M. (1968) American Kinship: a Cultural Account, Prentice Hall Craig, D. (1979) Am. Anthropol. 8 1,94-95 Strathem, M. (1992) After Nature: English Kinship in the Late Twentieth Century, Cambridge University Press Layton, D. et al. (1993) Inarticulate Science? Perspectives on the Public Understanding of Science and Some Implications for Science Education, Driffield Yorks: Studies in Education Ltd. Wood-Robinson, C. (1994) in Learning Science in Schools. Research Reforming Practice (Glynn, S. and Duit, R., eds), pp. 11 l-130, AAAS