In psychology, the problem of nature and nurture is one of the most controversial one. Behavioral geneticists have extensively explored the nature and nurture of general cognition, the etiology of specific abilities has received comparatively little attention. Conclusions about the relative impact of genes and the environment on different abilities are elusive because the few genetic studies of specific abilities have not yielded consistent findings as in the case of general intelligence. The lack of congruence seems attributable at least in part to differences and inadequacies of the statistical procedures used, as well as to differences in samples and measures (Ridley, p. 54). The environmental outcomes indicate that although shared sibling environments do not exert a measurable effect in our sample, nonshared environmental factors play a large role in specific cognitive abilities. The unique environmental factors are important at each age and exhibit some lasting effects over childhood. The finding of environmental persistence through g and not specific factors implies that childhood experiences may have important consequences for a particular ability at the time of occurrence but may have generalized effects on mental skills at later occasions.
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The example of gay parents suggests that genetic factors are more impotent than social influences because children do not change their sexual orientation influenced by same sex marriage of their parents. Educational or rearing changes that might facilitate verbal learning at one age also may facilitate verbal and performance abilities in later childhood (Ridley, p.58). Continuity of unique environmental effects is rarely seen in family studies of cognition, but the present environmental findings are not confounded with test measurement error as in most behavioral genetic models. Therefore, these effects should reflect real environmental influences, and their persistence should reflect a genuine developmental trend. Another technique for studying the nature-nurture topic, which has been made available through modern genetics, is gene linkage analysis. This technique allows researchers to search for genetic or familial abnormalities that tend to occur together and thereby place them on the same chromosome (Wallen, p. 364). With this technique, researchers can even determine the distance between two linked genes. Behavioral genetic analyses provide information about individual differences in the structure of traits. Behavioral genetic analyses also provide evidence for three generalizations about the structure of intellect. First, ordered relationships among components of aggregate indices of intelligence are partially derivable from the heritability of components. Omnibus measures of intelligence are based on aggregates of responses to diverse intellectual tasks (Bagemihl, p. 43).
The example of gay parents shows that genetic predisposition is more important that psychological and social influences. This phenomenon is explained by the fact that with thousands of genes expressed in the nervous system, ample room exists for genetic variability in its function (Ridley, p. 75). Behavioral genetics theory further attributes the transmission of personality between generations, at least partly, to the transmission of genes; and it attributes differences in population means from one human group to another, at least partly, to accumulated individual differences. With these features in mind, this theory does little to explain the total sociocultural context (Wallen, p. 364). According to findings on inherited personality traits, some people should be outgoing and gregarious, and some people should be shy. But a behavioral genetics approach cannot say whether these individuals will be riding horses or driving cars, or whether their economy will be based on farming or on industry. In Gestalt psychology’s metaphor, behavioral genetics may miss the “ground” of cultural averages against which the “figure” of individual differences stands out.
Social And environmental impact
The example of twins brought up separately portrays that genetic factors play secondary role in contrast to social conditions and upbringing. The etiology of a trait does not indicate exactly how a trait works its effect. The transition from how much variation is explained by a particular source (i.e., genes or environment) to how that effect is produced is a long and arduous one (Tieger and Barron-Tiege, p. 65). This statement is true regardless of whether one is considering the physiological or psychological realms of explanation. The discovery of a heritability of 50% doesn’t indicate in which brain location these physiological differences reside or how they do their work. In the psychological realm, traits may modify behavior because people become consciously aware of their internal (biological trait) capabilities as well as their external (environmental) constraints and opportunities (Ridley, p. 51). The role of self-awareness in completing the circuit between traits and behavior is not well explained in behavioral genetics. If the great enthusiasm for cognitive models of behavior is to be followed, then the explanation of behavior must involve some kind of computer simulation of process mechanisms (provided that the simulation is not so complex as to be incomprehensible). Behavioral genetics is very good at accounting for trait variation; it is poorer at accounting for mechanism, especially when the “mechanism” and outcome may be in different realms of analysis. But certain theoretical formulations within behavioral genetics allow for greater illumination of mechanistic questions. For example, statistical techniques exist to assign composite variance components to specific environmental influences or to specific genes. Those personality researchers and teachers who want more than a “textbook knowledge” of behavioral genetics should seek these conceptual formulations and the related findings (Pervin, p. 43).
Twins Brought up Together
The case of twins brought up together shows the correlation of traits with developmental outcomes. For example, infant-mother attachment is associated with different temperamental traits. Process interpretations of this association differ, however. Environmentally, it may reflect either general child-rearing style as a shared environmental influence or the specific learning history of infant-mother interaction. Genetically, the kind of attachment children form may depend on their genetic trait dispositions (McKnight, p. 87). Given these different process models, a twin study could be conducted to determine whether the phenotypic association of attachment and temperament is mediated genetically or environmentally, and if the latter, then whether shared or nonshared environmental influences predominate. The unique learning history process model would suggest that the attachment—temperament association is dominated by nonshared environment. Thus, behavioral genetics analysis may reveal how two variables are associated in terms of causal genetic or environmental mechanisms (Parsons and Bales, p. 101).
Personality researchers and teachers, then, should be aware that behavioral geneticists have actively sought to test assumptions of their models; indeed, critics often complain that the methods are biased, without offering empirical evidence. The main point is that a violation of assumptions requires several facts to hold: (a) some form of unequal treatment according to twin type or adoptive child versus biological child, (b) some form of nonrandom placement, and (c) a relationship of treatment or placement to trait variation. In studies of reared-together twins, it is the last point in this reasoning that is the weakest (Tieger and Barron-Tiege, p. 87). Psychological environments differ among families: Some parents impose relatively strict rules on their children, whereas others are permissive; some parents display warmth and affection overtly, whereas others are cold and unemotional; some parents are cultured and interested in politics and foreign places, whereas others are more parochial. Economically, even excluding the poorest families, American families differ tremendously in their economic security and accumulated wealth. Personality teachers and researchers should be aware that rearing environments that appear to be psychologically different may be functionally equivalent for children’s development. In behavioral genetics, evidence for the functional equivalence of family environments comes from a lack of between-families environmental influence on many traits. Children’s average phenotype on personality traits differs among families. But average differences in phenotype can arise from differences in parental genotypes as well as from differences among families in the specific environmental influences that siblings share (Wilson, p. 76).
Personality researchers and teachers should be aware that associations between psychological environments and developmental outcomes may be genetically mediated. Genetic variation can cause variation in psychological environments through its influence on behavioral phenotypes. The psychological environment, after all, is a product of some person’s behavior—a parent, a teacher, or a peer. Insofar as heritable traits and dispositions affect that person’s behavior as an environmental stimulus to another person, variation in what we label as environment can be etiologically genetic (Wilson, p. 54). In some situations, the association between the psychological environment and developmental outcomes is genetically mediated. The passive genetic correlation between parent and child is a prime example. The same cluster of genes may produce two disparate behavioral effects: In a parent, they may influence variation in child-rearing styles; whereas in a child, they may influence variation in outcome traits. This pathway of common causality is possible because a child shares half that parent’s genes through either the egg or sperm cell (Wilson, p. 31).
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This pathway of genetic mediation of environmental association renders much of the research on childhood socialization ambiguous as to the relative influence of genetic and family environmental influences because family members are related genetically as well as environmentally. Social class statuses are attained by individuals through their own efforts in education, job selection, and climbing up corporate and institutional hierarchies, all behaviors that may be directly and indirectly influenced by a broad range of heritable intellectual and personality traits. Briefly, family environmental influences may become more important at environmental extremes (Tieger and Barron-Tiege, p. 44). Thus, one may find evidence for greater shared environmental influences in particular social contexts. Models can test this by examining whether parameter estimates of shared environmental influence vary with environmental context. Furthermore, environmental influences may be nonshared and experienced uniquely by each family member. Behavioral genetics models can also examine the nonshared influence of specific environmental measures (Wilson, p. 41).
Nature vs Nurture Discussion
The examples of gay parents prove that genetic factors are important determinants of personality development. Sometimes missed in developmental psychology’s focus on families, is that environmental influence can occur through a host of nonfamilial routes (Tieger and Barron-Tiege, p. 65). Most broadly, a reproduction of environmental context occurs through existing social institutions that structure the education of the young and the means of economic production. More narrowly, environmental influence occurs through same-age peer groups and through adults other than parents, including teachers, other biological relatives, and acquaintances. Dramatic environmental changes may spread through nonfamilial influence routes to produce changes in developmental outcomes. Thus, interventions need not proceed merely through local family environment but can be communitywide (Wilson, p. 77).
In contrast to gay families, the case of twins brought up separately shows that social and psychological differences in families are important for personality development. Furthermore, a moderate heritability does not mean an absence of social influence on how traits are expressed as different behavioral outcomes. These ideas receive less attention in developmental psychology because of the discipline’s primary focus on development in the family context, but they are part of a broader social science perspective (Tieger and Barron-Tiege, p. 33). Environmental conditions can modulate a temperamental profile. Daily experiences permit some children to control their irritability and later their fear. It is even possible that experiences that reduce levels of uncertainty can alter the excitability of the limbic system through changes in the density of receptors on neurons. There is always the opportunity for the child to learn to control the urge to withdraw from a stranger or a large dog. The temperamentally shy child is not chronically helpless; remember, lions can be trained to sit quietly on a chair even though that posture is not typical of their species. Indeed, the role of the environment is more substantial in helping the child to overcome the tendency to withdraw than in making that child timid in the first place. No human quality, psychological or physiological, is free of the contribution of events both within and outside the organism. No behavior is a first-order, direct product of genes (Wilson, p. 55). Classical behavioral genetics methods like twin and adoption studies have been instrumental to the fall and rise of genetic. Modern molecular genetics techniques are likely to play an increasingly important role in future studies aimed at identifying and characterizing genetic influences. It is clear that the genetic how and the environment how will need to be integrated in ways that reflect both the unique and the combined influences of genes and environments (Tieger and Barron-Tiege, p. 65). Integrating the genetic how and the environmental how is what is meant by bridging the nature-nurture gap. In addition to incorporating explicit measures of the environment conceptualized in systems terms and allowing for nonadditive synergistic effects in genetic—environment interaction, the model specifically posits empirically assessable mechanisms, called proximal processes, through which genotypes are transformed into phenotypes. Behavioral geneticists seek to infer the relative influences of various classes of genetic and environmental influences from patterns of covariation among individuals of varying degrees of genetic and environmental relationship (Berger, p. 52).
The research studies allow to say that nature and nurture are parts of the personality development. Genetic development determines the main characteristics of a child and predisposes his psychological development thus social influences and upbringing shape the personality and its development. Although the behavioral genetics framework is valuable for addressing at least the nine just-listed goals, it is not a comprehensive model for behavior. When critics overinterpret the behavioral genetics model to try to answer questions beyond its scope, misunderstandings occur. The most frequent overinterpretation is the attempt to make process-oriented interpretations from non-supplemented, traditional behavioral genetics data. Other misunderstandings involve failures to appreciate subtle distinctions between differences among individuals and the development of an individual.
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