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Common beliefs about the heredity of human characteristics.

The nature-nurture debate--that is, the question of the extent to which genetic and/or environmental factors determine human characteristics--is still one of the most controversial debates in psychology. For instance, the degree to which intelligence is attributed to heredity ranges from less than 40 per cent (Eysenck, 1981; Kamin, 1974) to about 80 per cent (Burt, 1971; Jensen, 1972). Others argue that the 'how much' question is inappropriate, and advocate an interactional point of view (Anastasi, 1979; Overton, 1973). Once people become aware of their own talents or shortcomings, they will try to shape their environment accordingly (Scarr & McCartney, 1983). For example, people with a feel for music are likely to start playing an instrument and short people will probably avoid playing basketball.

The scientific debate notwithstanding, lay people usually apply a simple additive model (Furnham, Johnson & Rawles, 1985). The present study deals with common naive estimates about the relative contributions of genes and environment to the development of human characteristics. The study does not concentrate so much on common beliefs about the heredity of specific character traits, but on the general belief as regards heredity. The study is based on the assumption that every individual can be located somewhere on a continuum which runs from strong environmental beliefs to strong genetic beliefs. In addition, it is assumed that the individual's place along this continuum is reflected by a general tendency to take a relatively strong heredity or environmental position, regardless of the nature of the specific characteristic considered.

Furnham et al. (1985) tried to predict people's heredity beliefs from a number of demographic variables. Some of these variables (age, sex and education) are also included in the present study. As such, the study can be regarded as a partial replication of Furnham et al.(1) However, our principal aim was to investigate the beliefs of two groups of subjects on heredity, groups which could be expected to be especially preoccupied with the nature-nurture question: social parents of adoptive children and people with an absent genetic parent. We thus compare the beliefs of a 'normal' group with the beliefs of a group of people who do not know the genetic backgrounds of their children, and a group of people who have incomplete knowledge of their own genetic backgrounds.



The sample consisted of 269 Dutch Caucasian adults (97 males, 172 females) ranging from 21 to 65 years of age (mean age: 37.4 years), divided into three groups. The first group (N = 53) consisted of parents who were raising one or more adopted children from Third World countries. The second group (N = 89) consisted of subjects with no personal knowledge of their genetic father, who were raised by their genetic mother and a social father. The third group, the 'normal' group (N = 127), was comparable to the adoptive parents group, in that all of the subjects in these groups were raised by both of their genetic parents, and to that of the absent father group, in that their children--if they had any--were their own genetic children. In addition to the subdivision in groups (adoptive parents, absent father or normal), the following subject descriptors were used: age, sex, marital status, presence of children, education and income. As the subjects in the group of adoptive parents have children by definition, the variable 'presence of children' is nested within the two remaining groups.


All subjects were asked to indicate their beliefs in heredity with respect to 16 diverging human characteristics. These items were selected on the basis of one consideration only: the characteristics were to be easily discernible and allow for the expression of individual differences with regard to beliefs in heredity. Apart from this criterion, they may be regarded as a randomly selected sample from the endless list of possible human characteristics. The 16 items covered in this study are, in order of presentation: stubbornness, tendency towards depression, creativity, intelligence, musical ability, energy, perseverance, neatness and orderliness, sportsmanship, collecting mania, body height, linguistic ability, tendency to addiction, fertility, humour and fear of heights.

For each item, the subjects were asked to indicate on a five-point scale the extent to which they thought the development of the specific characteristic was determined by environmental factors (score 1) or by genetic factors (score 5). The mean judgements ranged from 4.17 for body height to 2.49 for neatness and orderliness. Standard deviations ranged from .87 to 1.27, indicating that the discriminative value of each item was sufficient. Together the 16 items formed a homogeneous scale; Cronbach's alpha = .76.

The list we used in this study is clearly less balanced than the list of 48 items used by Furnham et al. (1985), in which six a priori categories (physical characteristics, psychological abilities/skills, personality, beliefs, psychological 'problems' and physical 'problems'/illnesses) were all equally represented. Items from the two physical categories were underrepresented, since most of them could be expected to produce ceiling effects at the genetic extreme of the scale, just as the introduction of 'beliefs' (morality, racial prejudice, etc.) would imply the danger of bottom effects at the environmental extreme. Factor analysis revealed that the factor solution was dominated by one factor (eigenvalue 3.6, explained variance 22.6 per cent). Apart from body length (loading: .22), all items had a substantial loading on this factor (between .36 and .61). Therefore, we concluded that the items have one main dimension in common.


The average score of the 'normal' group for the set of 16 items was 2.99 (SD = .49). This score is near the centre of the scale. The average scores of the two other groups suggest stronger beliefs in heredity than the normal group: 3.23 (SD = .46) for the adoptive parents group and 3.13 (SD = .44) for the absent father group. To check this conclusion, group differences were tested in a stepwise multiple regression analysis, in which all of the subject descriptors mentioned above, including their interactions, were entered. Moreover, as we wanted to take into account the possibility of curvilinear relationships, we also entered the squared variables: age2, level of education2 and level of income2 in the equation. A regression equation was found (F(3,265) = 14.62, p |is less than~ .001), containing three significant predictors, with multiple r = .38. It appeared that beliefs in the influence of heredity decreased with level of education (||Beta~.sub.educ~ = -2.48; SE (|Beta~) = .68). The second significant predictor was age. Beliefs in the influence of heredity appeared to be curvilinearly related to age (||Beta~.sub.age~2 = .0019, SE (|Beta~) = .00054), indicating that beliefs in the influence of heredity determinants increase with age and that this increase is more pronounced at more advanced ages. Thirdly, the beliefs of both the adoptive parents and absent father group with regard to heredity proved to be significantly different from those of the normal group. Adults who raise an adopted child and adults who do not know their biological fathers have stronger beliefs in the influence of heredity than do other adults (||Beta~.sub.group1,2~ = 2.55, SE (|Beta~) = .88). Together the three predictors explain 14.4 per cent of the variance of beliefs in heredity.


The findings on the first two predictors, education and age, are roughly similar to those of Furnham et al. (1985). People with a lower level of education and older people tend to have stronger beliefs in the influence of heredity. Like Furnham et al., we found that the relationship to age was best described in a curvilinear way. The more limited age range of the subjects in our study (21-65 vs. 16-70 in Furnham et al.) may have been the reason we found no evidence for the decreasing half of the inverted-U pattern. In the absence of younger subjects, we can state only that our results do not really conflict with Furnham's conclusion that 'people in the middle band' (|+ or -~ 25 to |+ or -~ 45 years) hold the strongest environmental beliefs. Furnham et al. (1985) also found that males are more environmentalist than hereditarian in their beliefs than females, a tendency which they attributed to the 'well-established finding' that women are more conservative. Just like Nilsson & Ekehammer (1989), we found no evidence for this claim in the present study. Sex did not appear in the regression equation and is probably no more than a mediating variable, related to education.

Based on the predictive value of religion and political orientation, Furnham et al. (1985) ascribed a key position to the notion of conservatism in explaining beliefs on heredity. They found that agnostics and atheists as well as people with left-wing views tend to attribute the origin of most human characteristics on the environment. The results with respect to age and education suggest that people with strong deterministic environmental beliefs not only adopt an ideology that the world and people can be changed (for the better), but probably also factually have the best opportunity to do so. Education makes vertical mobility possible, and the greatest moves upwards usually take place somewhere between age 25 and 45. Later in life, people tend to experience the ('genetic') limits of their abilities.

The principal aim of this study was to find out how the specific experiences of the two deviant groups have influenced their beliefs on heredity. It is interesting to note that marital status or the experience of raising children in themselves do not affect the tendency to believe in the influence of heredity. It is unlikely that parents refrain from comparing themselves with their children. Yet, this observation of similarities and differences apparently does not tip the scales in favour of beliefs in the influence of either the environment or heredity. For parents, it is presumably just as rewarding to consider themselves the genetic source of their child's characteristics as to ascribe these characteristics to their own qualities of parenting.

People who apply for adoption probably expect their child gradually to become 'their own child', despite the different genetic backgrounds. Therefore, it might be expected that these people hold relatively strong beliefs in the influence of the environment. However, if so, they do not maintain these beliefs after the adopted child has entered the family. Apparently ('genetic') differences are more salient than ('learned') similarities. Contrary to 'normal' parents, it is possible for adoptive parents to attribute all of the differences between themselves and their child to genetic factors, since they usually have no effective knowledge of the genetic backgrounds of their child.

The same line of reasoning can be applied to people who have incomplete knowledge about their own genetic backgrounds. Elsewhere, we observed that these people are indeed inclined to attribute most of their differences with their mothers (and social fathers) to genes inherited from their unknown natural fathers (Van Kampen, Koops, Meerum Terwogt & Reijnders, 1990). Again, a lack of knowledge about genetic backgrounds tended to hamper belief in the influence of the environment.

1 The original study was not designed as a replication study. We would like to thank an anonymous reviewer who brought the Furnham et al. study to our attention.


This research is part of a project financed by the Dutch Programming Committee of Youth Research (PCOJ), the National Fund of Mental Health (NFGV) and the Dutch Foundation of Children's Stamps (SKN).

The authors wish to thank Len Van Kampen, Arend Jan Van der Neut, Caroline Reijnders and Channah Zwiep for collecting the data.


Anastasi, A. (1979). Heredity, environment, and the question "How?". Psychological Review, 65, 197-208.

Burt, C. (1971). Quantitative genetics in psychology. British Journal of Mathematical and Statistical Psychology, 24, 1-24.

Eysenck, H. J. (1981). The Intelligence Controversy. New York: Wiley.

Furnham, A., Johnson, C. & Rawles, R. (1985). The determinants of beliefs in human nature. Personality and Individual Differences, 2, 675-684.

Jensen, A. R. (1972). Genetics and Education, London: Methuen.

Kamin, L. (1974). The Science and Politics of I.Q. New York: Wiley.

Nilsson, I. & Ekehammer, B. (1989). Social attitudes and beliefs in heredity: a replication and extension. Personality and Individual Differences, 10, 363-365.

Overton, W. F. (1973). On the assumptive base of the nature-nurture controversy: Additive versus interactive conceptions. Human Development, 16, 74-89.

Scarr, S. & McCartney, K. (1983). How people make their own environments: A theory of genotype |right arrow~ environment effects. Child Development, 54, 424-435.

Van Kampen, L. C., Koops, W., Meerum Terwogt, M. & Reijnders, C. J. (1990). Onbekendheid met de biologische vader als een belemmerende factor in de identiteits-ontwikkeling: een empirische exploratie (The unknown biological father as an inhibitor of identity development: an empirical exploration). Nederlands Tijdschrift voor de Psychologie, 45, 283-288.
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Author:Terwogt, Mark Meerum; Hoeksma, Jan B.; Koops, Willem
Publication:British Journal of Psychology
Date:Nov 1, 1993
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