Chapter 4. Genetics and Evolution
As discussed in Chapter 2, the biological perspective in psychology emphasizes bodily events and changes associated with behaviour. Biological psychology applies the principles of biology to the study of mental processes and behaviour. Psychologists in this framework study human behaviours that are both different and alike. We will begin this chapter with a discussion if the nature versus nurture debate. In this debate, psychological scientists seek to determine the origins of behavioural traits as being either biological or due to environment. Both sides of the debate contribute to the question, ‘why do we behave the way we do?”
Genetic and evolutionary approaches are biological perspective that inform this question. Genetic influence on behavior is a relatively recent discovery. Behavioural genetics is an interdisciplinary field concerned with how genes and the environment influence individual behaviour and traits including brain function. The focus of this field is on the genetic bases of individual difference in how we think and act.
Heredity and environment are constantly interacting to influence our psychological and physical traits. Epigenetics is the study of heritable changes in gene expression that does not involve changes to the underlying DNA sequence. Epigenetic research seeks to understand the influence of genes on our behaviour and mental processes, and how the environment affects our genes, and influences their expression through biological mechanisms that switch them on and off.
Behavioural genomics is the of study of DNA, inherited traits, and the ways in which specific genes are related to behaviour. This framework involves a shift in focus away from the influence of specific individual genes on behaviour to the entire genome which is an organism’s complete set of genes in each cell with the exceptions of sperm and egg cells. Researchers are interested in the interaction of multiple genes and numerous environmental factors that influence human behaviour. Methods using twin and adoption studies are engaged calculate heritability, which is a measure of variability of behavioural traits among individuals that can be accounted for by genetic factors. Variability in IQ scores, for example, can be denoted by a heritability coefficient, which is a statistic expressed as a number between zero and one that represents the degree to which genetic differences between individuals contribute to individual differences in a behaviour or trait found in a population.
While behavioural genetics and genomics perspectives focus on the roles of genes, heredity, and environment in explaining individual differences in behaviour, researchers in evolutionary psychology concentrate on the evolutionary mechanisms that might explain the commonalities that aid in our survival and reproductive success, including human cognition, development, emotion, and social practices. Evolutionary psychology is a field of psychology that emphasizes the evolutionary mechanisms at work in the similarities of human behaviour including cognition, emotion, development, and social practice. An evolutionary approach aims to interpret and explain modern human behaviour in terms of how our brains and behaviours have been shaped by the physical and social environment encountered by our ancestors, and the forces that acted upon them.
The theories of Charles Darwin have a profound influence on evolutionary psychology. Natural selection is a theory developed through his observations of the fitness of a species’ characteristics to its environment. Natural selection refers to the ability for a species to adapt to its environment, find food and water, and mate in order to stay alive long enough to reproduce and pass on genetic traits favorable to that setting. Evolution through natural selection requires a trait to be heritable, and individuals within the breeding population must have a reproductive advantage for having the trait. Evolutionary useful behaviors have had a beneficial function in the cognitive development of our species. The brain, for example, has a set of cognitive adaptations for solving problems related to survival and reproductive fitness. Individuals with advantageous traits are more likely to survive and reproduce offspring with similar genes.
While natural selection suggests that some traits and adaptations make an individual more likely to survive, certain traits evolve to help some individuals increase their chances of mating and passing on their genes. Darwin proposed a second theory to explain the fate of genes. Sexual selection theory suggests that certain traits evolve to help some individuals increase their chances of mating and passing on their genes. Members of the same sex will compete for access to the other sex in a process called intrasexual selection. Intersexual selection refers to the influence of physical factors signalling reproductive health and fitness, and cultural factors that indicate social security.
Sexual strategies theory is a comprehensive evolutionary theory of human mating that defines the menu of mating strategies humans pursue (e.g., short-term casual sex, long-term committed mating), the adaptive problems women and men face when pursuing these strategies, and the evolved solutions to these mating problems. Sexual overperception bias, for example, is a mating theory that suggests that males often misread sexual interest from women to prevent the costs of missing out on an opportunity for reproduction. Evolutionary research on attraction also highlights the importance of facial symmetry to mate selection and reproduction.
Sociobiology contends that evolution has given us a genetic tendency to act in ways that maximize our chances of passing on our genes onto the next generations. Psychological traits are thought to be ‘selected’ to aid individuals in propagating their genes. Hunter-gatherer theory illustrates sex differences and suggests that our labour was divided based on sex and sex role socialization as a means of survival (Buss & Barnes, 1986; Silverman & Eals, 1992). For example, this theory suggests that males hunted, and females gathered because of physical and behavioural skills that are reproductively fit to this environment, an also, that some competencies selected for during the process of human evolution are still present today. This can be a very controversial area of theory and research as you will see in the highlight ‘How We Talk (or Do Not Talk) about Intelligence’ in Chapter 9.
Biopsychosocial theory takes a complex approach to understanding human behaviour. Aspects of biology (genes), psychological components (thoughts, personality, mood), and social conditions (family support, stress, culture) are all considered in analyses of why we do what we do from this perspective.
Research in the evolutionary perspective also applies the principles of biology to the study of human behaviour. Evolutionary psychologists start from the position that cognitive structures are designed by natural selection to serve survival and reproduction (Hagen 2004). From this perspective, hearing, smell, vision, pain, and motor control are examined as functions of the nervous system that have been involved in survival and reproduction for thousands of generations and years.
Buss, D. M., & Barnes, M. (1986). Preferences in human mate selection. Journal of personality and social psychology, 50(3), 559.
Hagen, E. H. (2004). The evolutionary psychology FAQ. NOBA Open Textbook Project. Retrieved from http://www.anth.ucsb.edu/projects/human/epfaq/ep.html
Silverman, I., & Eals, M. (1992). Sex differences in spatial abilities: Evolutionary theory and data. In Portions of this paper were presented at the meetings of the International Society for Human Ethology in Binghamton, NY, Jun 1990, the Human Behavior and Evolution Society in Los Angeles, CA, Aug 1990, and the European Sociobiological Society in Prague, Czechoslovakia, Aug 1991. Oxford University Press.