Essay Question: To what extent do genes affect behavior?
The present essay will discuss the extent to which genes affect human
behavior by analyzing depression, both as a result of biological determination and as
a result of interaction with the environment. The study used for the first one will be the
one by Caspi et al, on the effect a structural change of a gene on the risk for developing
depression. The latter one will be explained through the study of Brown and Harris, on
the extent to which social and cultural factors play a role on the onset of depression.
One of the principles of the biological approach is that behavior is genetically
determined and inherited. In early psychological debates, behavior was argued to be
solely due to genes or due to the environment, leading to the dilemma of “nature or
nurture”. Nowadays, psychologists are not that absolute and the degree to which each
factor affects behavior is examined. On the part of genetic inheritance, genetics is the
field which examines the inheritance of both physiological and psychological traits from
generation to generation. The widely known DNA is the genetic material located in the
nucleus of each of our cells, containing instructions for the production of proteins,
which regulate the body’s physiological processes and the expression of phenotypic
traits, such as intelligence. DNA is organized in tiny units called genes, found on rodlike
structures called chromosomes. Each human being has 46 chromosomes, 23 of which
come from the father and the rest 23 from the mother. Siblings, with the exception of
identical twins, have half of their genome, meaning the total of their genes, being the
same, while the rest is unique. That 50% is what differentiates siblings, physically and
behaviorally. Genetic similarity, also referred to as relatedness, associates greater
similarities in the genes between two or more individuals to higher degree of
relatedness.
Genetic research is mainly carried out through correlational studies in twins,
along with adoption studies, and in families. Twin studies use a sample of twins, both
monozygotic (MZ), which are identical, and dizygotic(DZ), which are fraternal, and
compare the rate of behavior. If the behavior is genetic, it is expected to be mainly
observed in the MZ twins. The frequency at which we see a behavior in twins is the
concordance rate, which relates to correlational studies and thus, does not determine
causation. A more advanced form of twin studies are the adoption studies which use
twins that were raised together and twins raised apart, meaning that one or both twins
were adopted. If the same behavior exists between twins raised apart, in different
environments, the genetic argument is supported. However, many ethical concerns
are raised, as the twins might not be aware of the existence of the other twin and
finding a sample is quite difficult. The second type of genetic studies are family studies,
which look at the family tree of an individual, usually to study schizophrenia, suicide
and aggression. The process entails looking at data over a series of generations and
seeking for trends.
It appears, however, that genes solely code for potential and while there might
be a predisposition for the expression of a certain disease or behavior, the environment
is a determining factor to that expression. Behavioral genetics is concerned with the
understanding of how both genetics and the environment contribute to individual
variations in behavior. The increased amount of research from the sector of genetics
has led to the argument that there are several genetic markers, which do not, however,
work in isolation from each other or the environment, which appears to be the one
triggering the expression of a genetically-based behavior. Hence, a genetic
predisposition for a behavior, known as genetic vulnerability, will only be expressed
under the right environmental stressors. The conclusion that inherited factors provide
© 2020 Orsalia Toutouza All Rights Reserved
