A Critical Evaluation of Methods Used by Behavioral Geneticists
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Recent advances in the field of molecular genetics have put back the notion of a (partial) genetic determination of human behavior. The behavioral genetics as an interdisciplinary sub-field dealing with the heritability of specific behavioral traits is especially relevant in such fields as crime studies or risk perceptions’ studies (Jones, 2006). In the more general terms, behavioral genetics would be applicable to researching the problems of personal psychology at large (Plomin, 1986). Hence, the precise definition of this research field, as well as of the methods utilized by the behavioral geneticists, is still warranted, with a particular focus on the relative strengths and weaknesses of each of these methods. Then, it will be possible to hypothesize on the future directions of behavioral genetics as such.
The basic definition of behavioral genetics would seem to be rather simple. While neuroscience and cognitive psychology have often focused on the species-wide dimensions of human behavior, the behavioral geneticists explore the “within-species interindividual differences” that must be governed by “the…genes…responsible for the…heritability of behavioral dimensions and disorders” (Plomin et al, 2003, p.4). Thus, behavioral genetics is an interdisciplinary field situated at the cross-section of individual psychology and genetics that attempts to understand the complex links between specific individual behaviors and the respective individuals’ heritable traits.
Proceeding from this definition, several major methods used in the behavioral genetics research may be outlined. Furthermore, these would include family studies (e.g. twin studies, adoption studies), the molecular genetics methods (e.g. quantitative trait locus analysis, linkage analysis, and association studies), and animal studies (e.g. selection studies, studies of inbred generations, etc.). Each of these methodologies is characterized by its inherent limitations, strengths, weaknesses, and validity. Therefore, it is necessary to present their critical and comparative evaluation.
The family studies methods would be some of the easiest, and yet weakest forms of the behavioral genetics research. As noted by Plomin & Daniels (1987), differences between the children belonging to the same family and apparently sharing the same genome heritage would point at the importance of nonshared environment (i.e. the psychological environment’s variances) in the development of the family members’ psychological profiles.
At the same time, though, the use of family studies would allow the researchers to quantify the recurring features in the family members’ behavior, thus as to establish whether the occurrence of these traits is either heredity- or environment-based. In particular, the adoption studies may be used as an important data source in isolating the environmental factors’ influence from that of the familial genome.
For instance, Stoolmiller (1999) observed that, in his analysis of various adoption studies involving both collective and individual adoption models, which were centered at measuring children’s IQ and predilection for antisocial behavior, the family’s shared environment (SE) would account for more than 50% of the respective IQ effects. The usage of quantitative methods would thus enable the researchers to specify the SE-induced behavioral effects, and then to establish the purely genetics-based behavioral patterns among the family members with shared heredity traits. Due to this factor, the validity of the adoption design may be acknowledged even by some outspoken critics of behavioral genetics (Stoolmiller, 1999, p.392).
The twin studies is another important form of the family studies methods practiced by behavioral geneticists. This methodology would allow for establishing the precise correlation between the twins’ genetic traits and their general behavioral patterns. In particular, the differences between identical twins (sharing the common genome) and fraternal twins (possessing only a half of common genes among themselves) may be extremely relevant for the purposes of tracing relative effects of genetic and environmental factors in behavior’s development. For instance, Kaprio, Pulkkinen, & Rose’s (2002) study on the relationship between genetic and environmental factors in health-related behaviors among 2,733 Finnish adolescent twin pairs, thus allowed the researchers to differentiate between their genetic- and environment-influenced behaviors, leading to the practical policy recommendations.
On the other hand, the twin studies’ design may be less reliable than that of the adoption studies, for the twins’ numerical frequency among the population may be rather low, and the assumption on their shared environment may not always be valid as demonstrated, among others (Kaprio, Pulkkinen & Rose, 2002). These two factors would make the twin studies a rather problematic method of the behavioral genetics studies.
The molecular technologies-based methods generally depend upon the gene localization techniques that would enable the researchers to identify the transmission of specific genes and their alleles across the individuals with shared heredity. For instance, the linkage analysis methodology may be used in order to map the occurrences of the alleles responsible for specific behavioral traits such as quantitative trait loci (Ghosh, Reich, & Majumder, 2002). However, in this case, the main problem is that the utilization of the exact statistical procedures may be possible only for the Mendelian heredity’s instances, while the majority of human genetic traits “follow a complex mode of inheritance” (Ghosh, Reich, & Majumder, 2002, p.431), leading to lower reliability of the respective estimates. Together with the difficulties inherent in attempts to identify individual genes responsible for specific psychological traits may lead to significant failures in search for respective candidate genes (Sanders et al, 2008). These two factors would significantly limit the research validity of the molecular technologies-based methods.
Finally, the animal studies methods rely on the observations of correlations between the experimentally observed animals’ mating patterns and the behaviors of their offspring generations. As the scientists are able to control for the selection of the experimental subjects’ mating partners, the influence of genetic factors and their interrelationship with the environmental ones may be easier to observe than in the case of human populations (Wehner & Balogh, 2003). However, at the same time, it may be difficult to apply the experimental findings obtained from observing the nonhuman species’ behavior in experimental conditions to the human populations with the markedly different genome systems and living environments (Tordjman et al, 2007). This may be the research design’s major weakness and limitation.
Therefore, behavioral genetics appears to be experiencing a revival, with a number of methodological approaches being used to explore the discipline’s main issues. Proceeding from the perspectives outlined above, it is possible to conclude that the behavioral genetics’ future would depend on a careful combination of all these research approaches, to eschew their weaknesses and overcome their limitations.