Primary propositions for the selection theory of interests, essay in VocationalPsychology.com

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The Selection of Interests:
Part 2
by Andrew D. Carson, Ph.D.

Primary Propositions: Genetic factors

Proposition one: A limited set of "potential" interests are inherited through genes. It is assumed that individuals inherit a set of genes associated with at least a small set of potential interests, along the same lines as speculated by Lykken et al. (1993) in their discussion of "primary" interests. As a metaphor for the process through which genes might have an impact on the development of interests, consider a specially constructed piano keyboard than one "inherits," and in which the set of keys represents the full set of such potential interests that can be influenced by genes. To elaborate the analogy, only some keys (interests) are connected via hammers to strings (i.e., only some of these primary interests are "connected" or "playable" to any given individual). Thus, genes serve to directly restrict the potential for the eventual acquisition of interests, and this apart from any environmental contribution. This assumption is similar to Holland's (1985a) assumption that there exists some contribution of genetics to the development of vocational personality types. However, in the selection theory genes play a more central role than in Holland's. Where Holland suggests that inheritance implies only "a little push in one direction as opposed to another" (p. 16), the new evidence suggests a the existence of a large push in one or more directions. This first proposition is quite similar to Roe and Lunneborg's (1991) primary proposition regarding the influence of genes on interests, namely, that "genetic inheritance sets limits on the potential development of all characteristics, but the specificity of the genetic control and the extent and nature of the limitation are different for different characteristics" (p. 74). And as already noted, the Betsworth et al. (1994) report, together with the other studies suggesting a genetic basis of interests (e.g., Loehlin & Nichols, 1976; Vandenberg & Kelly, 1964), collectively provide ample evidence for a genetic substrate to interests, albeit possibly one working through the effects of other genetically influenced variables, such as aptitudes or temperaments. However, one might just as well suggest that one can inherit interests in the exercise of particular aptitudes, given appropriate environmental opportunities for such exercise, so the causal direction here is by no means certain. It may make more sense to speak of genetically influenced patterns of interest-aptitude-temperament, rather than to focus on these variables singly.

Proposition two: Critical periods exist during which environmental factors may most readily select potential interests. From this set of potential or playable interests, there exist affordances, both endogenous and environmental, which may serve to "play" or "exercise" those interests. However, an individual's responsiveness or sensitivity to such affordances may and probably will change over time, resulting in "critical periods" in the development of interests and personal orientations (see also Collaer & Hines, 1995, p. 94). To extend the piano metaphor discussed in reference to proposition one, even the playable keys that are connected to strings are maximally playable only at certain times; once that critical moment passes, the ability to create an audible note from striking the key diminishes, and past a certain point no amount of striking the key will produce the desired sound. As a construct, the critical period has a long history in both psychology and biology (see Kandel & Jessell, 1991, ch. 60), although its application to a topic associated with vocational psychology and the development of talent may strike some as unusual (for an exception, see Casey and Brabeck's [1989, 1990] discussion of the development of spatial skills needed for a variety of high-spatial careers; also, Casey, 1995). Nevertheless, the concept of the critical period is essential for the selection theory of interests.

Holland (1985a) does not incorporate critical periods per se into his theory. Instead, he relies primarily on a social learning model to account for how parents and other environmental sources may reinforce particular facets of vocational personality types and interests toward particular directions. In addition, Holland (1985) adopts a "like produces like types" argument, suggesting that only homologous affordances (or, within the context of ethology, "releasing mechanisms") select interests. However, the selection theory of interests depends not only on critical periods, but also does away with the restriction of homologous affordance. In other words, seemingly unlike types can produce types. Even Holland (cited in Osipow, 1983, p. 92) has reportedly found some evidence that nonhomologous affordances affect the development of interests, with parents who hold democratic attitudes and values having sons who to tend toward investigative personal orientations, while parents with authoritarian attitudes and values having sons who either tend toward realistic or social personal orientations. Admittedly, this is not a strong example of nonhomologous affordance at work, but it does document the general point because for a stimulus to be homologous for the Realistic type, one would assume that it would have to be non-homologous for its opposite type (Social) within the hexagonal structure of interests. In any event, this feature of the selection theory bears some (distant) resemblance to Holland's (1959) comments in his original theory statement which implied that certain environmental events at specific developmental periods might tend to "fixate" the development of personality, and thus indirectly the development and relative magnitude of personal orientations.

Roe's (1957) theory of the importance of parenting environments for young children also seems to incorporate the notion of critical periods. Roe's original theory followed closely on the heels of compelling evidence reported by the psychoanalyst Ren‚ Spitz (see Kandel & Jessell, 1991, p. 946), whose comparison of two early childrearing environments (one resulting in relative social and sensory deprivation) provided strong evidence for the existence of an early critical period for socialization in humans. Unfortunately for Roe's theory, tests were not consistently supportive that differences in early parenting environments affected eventual career choices substantially (Osipow, 1983, pp. 20-31; Trice et al., 1995). However, there now exists substantial evidence to support her general contention that the quality of early parenting during a critical period can influence the development of personality traits that have been shown to affect a number of personality characteristics that themselves appear to affect adjustment to important areas of adult functioning, including adult career development. For example, Muchinsky (1994) reviews the literature on the relations between life history factors and vocational interests and choices, concluding that "the life history factor having the most consistent effect on vocational behavior is relationship with one's parents" (p. 539). In retrospect, Roe's (1964) contention that secure attachment to caregivers in early childhood might be associated with vocational outcomes appears far-sighted; her hypothesis was that secure attachment would be lead to enhanced movement of the child toward person-oriented occupations. Although Trice et al. claim that this aspect of Roe's theory never has received a direct test, Roe's reports (see Osipow, p. 22) of the life histories of eminent scientists do suggest differences between groups of scientists in the degree to which the family experienced disruption during childhood, with biologists reporting a much higher percentage of either parental death or divorce, while among the social scientist group divorce was absent. Roe (see Osipow, p. 21) also found that prolonged isolation during childhood, such as might be the case with children having experienced prolonged illness, was also commonly reported among scientists, especially theoretical physicists. At any rate, Roe's identification of the importance of examining the quality of attachment in early childhood would today put her in the mainstream of thought within counseling and career psychology (Blustein, Prezioso, & Schultheiss, 1995; Kenny, 1994; Lopez, 1995).

There also exists a long tradition in personality psychology -- most particularly within the psychodynamic schools -- that assumes that there exist (essentially) critical periods in the formation of the personality in early childhood, with lasting effects on development and adjustment, including occupational interests, choice and adjustment. For example, within the Adlerian tradition, several authors (e.g., Hafner & Fakouri, 1984; Manaster & Perryman, 1974; see Watkins, 1984) have argued that "early memories represent particularly valuable windows on those core aspects of personality that help to determine both the individual's choice of and quality of adjustment to his or her occupation" (Carson, 1994, p. 150).

Finally, both external environmental and endogenous triggers serve to select and preserve interests. An important class of endogenous spurs for the selection and preservation of interests must be a variety of substances generally classified as hormones (functioning on organs of the body as hormones, or on neurons as neurotransmitters; McGuigan, 1994, pp. 212-213). As early as 1957, Super speculated that hormones ("endocrine tendencies," p. 81) contribute to the direction of career development. In their recent review article, Collaer and Hines (1995) summarize the empirical and clinical literatures related to the role of gonadal hormones in the development of sex differences, and they present sweeping evidence for their impact on a variety of sex-typed traits, including stereotypically masculine and feminine play preferences in childhood. Moreover, they argue that the effects of such gonadal steroids appear to begin during fetal development, before environment-based learning can occur. The intrauterine hormonal environment experienced by the developing fetus would thus affect the resulting interests of babies and young children. Sex differences in toy and play preferences in childhood as summarized by Collaer and Hines may advance ineluctably toward the sex-related differences in task and work preferences (i.e., vocational interests) observed in adulthood. Therefore, Collaer and Hines' data are consistent with an account of sex-related differences in vocational interests during adolescence and adulthood that arise -- in part -- from sex-related differences in testosterone (and other hormone) levels in intrauterine and early postnatal environments.

The task of identifying the precise ways in which hormones and neurotransmitter levels serve to regulate and perhaps select interests is made more difficult, however, by the sheer magnitude of the research problem. Humans generate hundreds of hormones, and their effects might be in combination as well as direct. Data such as those reported by Collaer and Hines (1995) do make the initial task easier, as they implicate gonadal hormones in the development of interests in childhood. It is also likely that some of the same neuroendocrine systems that regulate depression and mania in pathological cases must in some way be involved in the normal regulation, and possibly in the selection, of interests. Manic individuals tend to exhibit elevated interests, while depressed individuals exhibit generally reduced interests, as measured by standard inventories (see Spokane, 1991, p. 251). Thus, it seems plausible that serotonin- and perhaps norepinephrine-associated neurotransmitter systems are implicated, at least with the preservation of established (i.e., selected) patterns of interests. The euphoria and excitement that is associated with the "discovery" of activities in which one senses a profound sense of attachment and fit -- presumably the precursor of a process through which that interest may be selected for preservation -- further suggests that the endogenous endorphin system and perhaps the adrenal systems may be involved in the process through which interests are initially selected, at least through a process of "positive" selection. It is also conceivable that other neuroendocrine processes may be implicated in a process of "negative" selection of interests, in which potential interests are removed from further consideration or somehow blocked, perhaps through association of an activity with traumatic stress. Thus, the same sort of neurophysiological processes implicated in the genesis of traumatic stress disorder may also play a role in the extinction of interests.

Proposition three: Almost all potential interests are associated with multiple combinations of genes, of which at least some important ones are located on the Y-chromosome. So far, little has been said about the particular location of genes related to interests, that is, on which chromosomes they are located. While it is possible (if unlikely) that some specific interests are controlled or strongly influenced by single genes, it is much more likely that expression of interests could depend on the interplay of a number of different specific gene sites (along with environmental factors), each with potentially different roles at different points in development. As Wilson (1978/1979) noted, "there are hundreds of thousands of variables to consider" (p. 75). Knowledge of human genetics has not reached the point, at any event, to begin to untangle that Gordian knot, although there has been rapid progress along these lines in the study of medical diseases.

An interesting question lies in whether it is possible (or perhaps even likely) that some genes contributing to the selection of interests are located on the Y chromosome, which only men have. If that is the case, then there may be some potential interests to which either sex simply do not have "genetic access," or at least have different patterns of access than those that are available to the opposite sex. Some interests may be toggled "on" due to the presence of Y chromosome genes, e.g., through the influence of gonadal hormones. Other interests might be toggled "off" by the presence of a Y chromosome. Still others might be toggled on in the absence of the Y chromosome; in such a case men would not have direct access to certain potential interests. Individuals might, however, be able to act as if they had such areas as a result of learning (see below). Investigators in the field of interests have known for some time that men and women, on the average, are often interested in different types of things. Rather than dismiss these differences entirely as being due to the effects of differential sex-role socialization, one might suggest the existence of Y chromosome linked interests (or, at least, facilitating tendencies for such interests). Thus, selection theory could provide a reasonable alternative account for the existence of sex-related differences in interests. In a study comparing the responses of MZG and DZG twins to the Vocational Preference Inventory (VPI; Holland, 1958), Nichols (1968) reports data suggesting that the degree of genetic influence on specific (item-level) interests differs between men and women, noting that "whatever is making identical twins more alike than fraternal twins is either not the same or is not operating in the same way in the two sexes" (p. 15). However, the VPI scale-score differences between male and female respondents do not appear to differ significantly, perhaps suggesting that sex differences in genetic factors affecting interests play a greater role for specialized interests than for more general personal orientations.

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