Chapter 21: Biology and Personality

Part 1: Biology and Personality

During the evolution of the human species, we appear to have lost the ability to rely on instinctive behavior as we developed extraordinary abilities to learn and adapt to the conditions facing us in our environment.  In addition, we can pass on that learning to other members of our social group. This is the basis for culture, and the success of the human species is a testament to the advantages of this approach to survival. However, this transition from instinct to learning and culture has not resulted in the elimination of biological influences on our behavior.  Certain groups of people, usually a minority of the population, retain biological predispositions to behave and react in certain distinct ways. To a lesser extent, all of us have some degree of these biological predispositions.

The purpose of this chapter is to examine those biological predispositions that are directly reflected in aspects of individual personality.  Over 2,500 years ago, Gotama Buddha came to a fascinating understanding of the human mind. The Buddha taught a series of mindfulness exercises to train the mind, and these mindfulness exercises form the basis for many styles of meditations. Today, cutting-edge neurobiologists are using functional magnetic resonance imaging (fMRI) and other brain imaging techniques to examine brain activity during deep meditation.  The goal of these studies is to understand the nature of the human mind, and to examine whether the Buddha (as well as the Rishis and Yogis of ancient India) had discovered a way to actually alter the state of the mind. However, too much time spent in meditation can lead to a weak body.  So, the founder of Zen Buddhism, Bodhidharma, when he arrived at the Shao-Lin temple, developed techniques of physical training to strengthen the monks and to help them both defend themselves from bandits and prepare for extended periods of meditation. This was the legendary beginning of the martial arts, formal techniques to train the body and mind.  Since the martial arts were developed with noble goals, they have throughout their history had a reputation for developing strong, admirable character traits. In other words, those who practice martial arts with proper discipline also train themselves to conform to a personality style marked by a calm, humble, yet confident demeanor.

This is a black-and-white photograph of a group of adults stretching before an Aikido lesson.
Source Image: Abelleee. Retrieved from Pixabay at Licensed under CCO.

Some 2,500 years ago, Gotama Buddha presented what can be considered the first psychological theory, a theory on the nature of the human mind and how one can work to control it in a mindful way.  Doing so can help to lead one toward a more peaceful life, both individually and in relation to others. Today, neurobiologists using cutting edge technology are trying to determine what actually happens to the state of the human mind during the techniques of meditation taught by the Buddha.  In addition, the usefulness of meditation and mindfulness in psychotherapy is a popular area of clinical practice and research, as well as a means toward enhancing the cross-cultural perspectives of psychology in general.

Wilhelm Reich, a student and highly respected colleague of Sigmund Freud, was one of the first Western psychologists to consider the connection between body and mind as essential for psychology health.  According to Reich, we can be psychologically healthy only if we are able to fully express and satisfy our biological, sexual needs. Reich devoted his career to helping individuals do just that, and in recognizing the role of the body, he anticipated the field of sociobiology.  Sociobiology addresses the ways in which our behavior might have been shaped by evolution. In other words, behaviors are naturally selected if they provide an advantage for our genetic reproduction (having children, grandchildren, etc.).

Whereas Reich and the sociobiologists focus on the expression and pursuit of our biological desires, Eastern tradition taught ways to train the body and mind to control these desires.  Indeed, the Buddha taught that through mindfulness training we could detach ourselves from these needs and live a life in which we acknowledge desires but feel no attachment to them. Such mental discipline, however, requires practice.  As monks became physically weak from spending all their time meditating, the founder of Zen Buddhism, Bodhidharma, developed the first formal techniques of Kung Fu. Since the martial arts arose out of the desire to remain healthy during meditation practice, they have always been associated with a spirituality devoted to nonviolence and mental discipline.

Twin Studies, Adoption Studies, and Family Studies

When talking about the role of biology in behavior, the natural starting point is the genetic makeup of each person.  Our specific genetic blueprint is what distinguishes each of us as a unique individual, except for identical twins. However, since humans no longer rely on instinctive behavior, there are no aspects of personality that are specifically determined by genetics.  Instead, it is more appropriate to say that our genetic makeup determines ranges within which we might develop, and our environment then determines where we fall within that range. The topics of greatest interest in the biology of personality are those topics that appear to be under a relatively greater influence of genetics than environment.  But how do we determine the relative contributions of genetics and environment? Psychologists have relied mostly on twin and adoption studies.

Twin studies have a long and interesting history in the field of psychology.  Sir Francis Galton (1822-1911) studied mental abilities and is recognized as being the first to utilize twin studies.  His use of identical twins in the mid to late 1800s is generally recognized as the first use of an experimental control group (Diamond, 1977/1997; Jensen, 1998), and the use of identical vs. fraternal twins continues to be recognized as a natural control condition by psychologists and sociobiologists (Kagan, Kearsley, & Zelazo, 1978; Wilson, 1978).  Twin studies were also of interest to psychologists in the former Soviet Union (Cole & Maltzman, 1969). While Anna Freud and Melanie Klein were applying psychoanalysis to the study and treatment of children, the American physician and psychologist Arnold Gesell was comparing the achievement of fundamental developmental milestones between twins (Lomax, Kagan, & Rosencrantz, 1978), and Wayne Dennis was conducting an astonishing experiment on a pair of twins.  Dennis and his wife raised the twins under conditions of minimal social and sensory stimulation. This research had a noble goal: to understand the basis for the detrimental effects of institutionalized care that was being recognized in overcrowded orphanages. However, one of the twins ended up showing signs of mental retardation (though this was attributed to an early head injury; Lomax, Kagan, & Rosencrantz, 1978). Obviously such an experiment would never be approved today due to the ethical guidelines and oversight that have become a common part of psychological research, but twin studies done in reasonable and ethical ways continue to be an important part of psychological research.

This image shows the faces of a set of adolescent, female, identical twins. They have long, blonde hair and blue eyes.
Source Image: Clard. Retrieved from Pixabay at Licensed under CCO.

What makes identical twins important is that they share 100 percent of their genetic material, whereas fraternal twins (like any other siblings) share an average of 50 percent of their genetic material.  By extending this to families, and finally to people who have no biological relationship, we have a continuum of genetic relatedness from complete to none. This allows us to address the issue of heritability, or the degree of individual variance on some measure of behavior or personality that can be attributed to genetics.  It is important to remember, however, that heritability is measured in populations (see Kagan, 1994; Sternberg, Grigorenko, & Kidd, 2005).  It makes no sense to suggest, for example, that a 5-foot tall person is 54 inches tall due to genetics and then grew another 6 inches thanks to good nutrition.

Adoption studies add an interesting twist to this research, since adopted children take the genetic contributions of their parents into different environmental situations, making adoption studies a useful tool for comparing the environmental contributions to the genetic contributions.  However, these studies remain challenging. For example, intelligence is perhaps the most widely studied trait in terms of whether and how much it is genetic. Some of this research has been very controversial. Sir Francis Galton, who was mentioned above, believed that his research confirmed that certain races were superior to others, and that superior races had an obligation to selectively breed their best individuals for the good of future generations, as had been done (and continues to be done today) with certain breeds of dogs and horses (Galton, 1869/1997).  Despite this controversial beginning to the study of genetics and intelligence, the topic has remained widely studied, but elusive nonetheless. Estimates on the heritability of intelligence range from approximately 65 to 85 percent (Gould, 1982; Jensen, 1998). However, at very early ages the genetic and environmental influences are closer to 50-50, decrease with age, and by adulthood, the genetic component is almost entirely responsible for the correlation of intelligence between related individuals (Gould, 1982; Jensen, 1998). Further complicating the situation for studying children, when a wider range of extended family members are considered and cultural factors are separated from non-transmissible environmental factors, it appears that genetics, culture, and environment all play roughly equal roles (Boyd & Richerson, 1985).  Indeed, culture can have profound effects on intelligence, including our definition of intelligence itself (Sternberg, 2004). Finally, returning to the controversial perspective of Galton and other proponents of the eugenics movement (the belief that superior races and classes should not mix with inferior groups), research today has demonstrated that no legitimate connection can be made between race and intelligence (Sternberg, Grigorenko, & Kidd, 2005; also see Loehlin, 1997; Williams & Ceci, 1997), and when it comes to education, IQ isn’t even the best predictor of academic performance (Duckworth & Seligman, 2005).

Another important point is the issue of family studies.  Usually, we think of the family as providing genetic similarity, since children inherit their genes from their parents.  Second, we tend to think that families provide a common environmental situation for each of their children, particularly in small families.  However, this is not always true. In the Russian literature there was a well-known case in which the first-born girl was always treated as the elder sister, even though her younger identical twin was only minutes younger.  The result of the differential treatment was that the “older” girl reached most developmental milestones before her sister (Bozhovich, 1969). In a case described by the renowned Russian neuropsychologist A. R. Luria, identical twins with retarded speech had begun to develop their own autonomous language.  Once separated into different classes in nursery school, however, the autonomous language disappeared (Luria, 1969). Thus, the family can have a very dramatic environmental influence, whether intentional or not, that goes against the genetic similarity due to biological relationships or even identical twinship.  What then, can we conclude regarding the heritability of personality traits in humans? Certainly genetic factors play an important role, but the complexity of the human organism and its sociocultural environment makes it difficult to draw definite conclusions about exactly how much of an influence our unique genetic profile has on our individual personality.  Nonetheless, psychologists have continued to pursue this important question.


Text:  Kelland, M. (2017). Personality Theory. OER Commons. Retrieved October 28, 2019, from  Licensed under CC-BY-4.0.


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PSY321 Course Text: Theories of Personality Copyright © by The American Women's College Psychology Department and Michelle McGrath is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.