Contextualizing Human Genetics

“Doubtless the greatest dissolvent in contemporary thought of old questions, the greatest precipitant of new methods, new intentions, new problems, is the one effected by the scientific revolution that found its climax in the Origin of Species.”

John Dewey, Essays on Pragmatism and Truth

Recent trends in the study of human behavior have focused on an integration of biological disciplines with traditional psychological methods of understanding the mind.  The interdisciplinary approach draws on molecular genetics, evolutionary theory, neural anatomy and physiology, and biological anthropology to illuminate the questions of how the human brain evolved, and the ways in which adaptations have impacted psychology and behavior.  The human as research subject has in recent history – and not without considerable controversy – been approached as an adaptive organism, the product of Darwinian processes.  This sea change suggests that the interface between social and biological sciences is where the study of Homo sapiens and their behavior should take place.

Recent years have shown an increased interest in the genetic influences on human traits and behavior.  Research investigating the genes that code for neurotransmission has revealed the profound ways in which our genetic structure helps to build the human mind, influence mood or impulse, and subsequently impact behavior.   Ongoing research into these relationships can have implications in pharmacotherapy, in addition to expanding our growing understanding of the genetic architecture of neural pathways.

Critical to understanding the implications of research in human genetics – and especially genes which impact behavior – is an appreciation for the complexity of relationships between genes.  Few genes show their phenotypic effects in a straightforward, Mendelian way; a common misconception is the notion that we have a “gene for A,” or a “gene for B.”  In reality, modern research has brought us to the understanding that genes work together in highly interconnected networks, influencing one another in complex ways prior to finding their phenotypic expression.  Occasionally a gene has a single, easily identifiable role, but most often it is active in a number of complex relationships with other genes.  Particularly in neural genetics, when the phenotype (our mind, moods and behaviors) is so complicated, it is essential to avoid the type of “gene for…” thinking in appreciation for the interactive properties of the individual genome.

Another common fallacy in the public understanding of genetics – and one very familiar to all geneticists – is the notion of genetic or biological determinism.  Particularly in the field of human genetics, it is crucial to clarify such a widespread misconception.  The field of human genetics provides an insight into the blueprints – our genes – which build our bodies, our brains, and (as we are now beginning to understand) contribute to our behaviors.  The extension of the phenotype beyond the individual body into behavior implies that mental life is never distinct or divorced from genetic factors.  However, while our perceptions, cognitions and behaviors are influenced by our genes, they are rarely if ever reducible to our genes.

The environment into which an organism is born is the stage upon which its genes are expressed.  As any ecologist can tell you, genetics alone do not determine the fate of any organism; rather, genes interact with the environment in a dynamic process.  This environment includes everything from prenatal conditions and food resources to predators and sexual competitors.  The environment can influence gene expression on a microscopic scale (i.e. the presence of bacteria) or a macroscopic scale (i.e. climate conditions).

The important point here is that genes are not expressed on a blank slate: they belong to a body, which is subject to any number of external circumstances.   In terms of human studies, this is why the fields of sociology or psychology are not irrelevant with the dawn of genetics.  Reductionism can have the tendency of impoverishing our science, and only an integration of multiple fields of knowledge will help to illuminate the story of our species’ evolution to the present. 

Discussion

Analysis of survey data revealed the previously reported relationships between Novelty Seeking scores and subjects’ sexuality.  SADI regressions show that individuals with higher NS scores report feeling greater desire for sex and arousal, and have less aversion or negative attitudes towards sexual contacts.

Interestingly, NS scores correlated positively with the QSF “Sexual (Dys)function – Self-Reflection” subscale.  This subscale supposedly measured dissatisfaction or “low function” in sexual performance of individuals.  Why would NS show a positive relationship to this subscale?  It should be noted that a number of items included in this subscale, designed to measure sexual dissatisfaction, also reflect sex-seeking or high-arousal attitudes (i.e. “Would you like to have sexual contacts more often?”; “Do you frequently masturbate?”).  This subscale also showed strong positive relationships with the Evaluative, Physiological and Motivational subscales of the SADI; thus, sexual ‘dissatisfaction’ does not reflect diminished arousal or desire for sexual contacts. In this context, NS is likely correlating to the sex-seeking behaviors contained within a scale designed for dissatisfaction.

NS scores correlated positively with scores on our Sexual Behavior Survey.  This is consistent with my hypothesis that greatest NS scores would correlate with a wider variety of sexual experiences in subjects’ life histories.  Additionally, the SBS gave a measure of subjects’ desire (yet unrealized) to have such a variety of sexual experiences.

Harm avoidance showed significant relationships to sexuality data which was consistent with the inverse regression of NS and HA (see fig. X).  Generally speaking, subjects with greater HA scores showed lower scores on arousal and desire inventories, and higher scores in terms of aversion or negative attidudes towards sex.

The negative relationships between HA and QSF (Dys)function subscales most likely reflect the sex-seeking behaviors contained within those QSF subscales (see discussion of NS above).

HA correlated negatively with Sexual Behavior Survey scores, suggesting that individuals with greater harm avoidance are less likely to seek out a wider variety of sexual experiences.  Similarly, high HA scores show a significant negative relationship to total lifetime partners and partners in the past year.  This could be reflective of harm avoidant subjects’ fear of contracting STDs or other dangers of promiscuous sexual behavior.

The Sexual Behavior Survey, while experimental in nature, proved itself to be consistent with other established sexuality scales.  This confirms my hypothesis that individuals with greater desire for sex or ease of arousal would seek out greater variety in terms of sexual experience.  Human sexuality exhibits a unique variety of styles, positions, and preferences in comparison to most mammalian behaviors (with the exception of some close primate ancestors).  This raises questions as to the evolution of primate sexuality in general.  We can safely assume that the Kama Sutra is not an adaptation for survival purposes; the task of research into human sexuality, then, is one of framing such unique human traits into alternate models of mental or cultural development.  My research here provides a clue to understanding such complex phenotypes.  Individuals’ variety of sexual behavior is related closely to more generalized drives toward sexual activity: arousal and desire, for example.

The lack of association found between genotype data and survey materials raises a series of questions.  As the role of DRD4 in novelty seeking is currently a matter of debate, the data presented here may reflect the lack of any association.  However, it should be noted that this study concerns only one marker on DRD4.  Many studies (including Zion et al., which originally reported the relation to sexuality) use multiple markers along DRD4 in haplotype analysis to search for phenotypic relationships.  It is possible that the 120bp duplication impacts the expression of other markers along DRD4, or even expression of other genes.

Future research into DRD4 should incorporate both haplotype analysis and gene-gene interactions.  Additionally, controlling for covariates such as age or religious background would help to clarify the phenotype, and thereby improve our understanding of neural genetics.

The relationships between neural architecture and human behavior are complex in themselves.  The current task is that of incorporating genes for neurotransmission (or any other aspect of the brain) into our understanding of mind and behavior.  This is naturally difficult given (a) the complexity of the phenotype, and (b) the interactive nature of our genes. 

This work represents the difficulty of studying the interaction between mental adaptations with clearly biological foundations and culturally influenced human behaviors.  Debates and arguments between the natural and social sciences are often concerned with this transition.  How much of the modern human mind is culturally (environmentally) influenced, and how much is genetic or the result of Darwinian adaptation?  Academic battles over sociobiology and evolutionary psychology highlight the ferocity of conflicting models.  Too often, the dichotomy between these approaches is widened by the inertia of disciplines which are perceived as distinct from one another.

Ultimately, the most lucid and illuminating models which emerge will be those that span multiple disciplines and approaches.  This is the theoretical space which connects the divide between “biology” and “culture,” rather than widening it.  The most compelling stories of our species’ past will undoubtedly occur along this bridge, and future years will show the ways in which these stories unfold.