Essay About Determination Of Human Behaviour And Twin Studies

Nature or Nurture – the Determination of Human Behaviour
Essay title: Nature or Nurture – the Determination of Human Behaviour
Nature or Nurture?
The Determination of Human Behaviour
The nature versus nurture debate has spanned over decades, and is becoming more
heated in the recent years. Following the mapping of the human genome, scientists are pursuing
the possibility of controlling human behaviour such as homicidal tendencies or insanity through
the manipulation of genes. Is this possible for us to ensure that humans behave in certain ways
under certain circumstances in future?
This is highly doubtful, as the determination of human behaviour depends not only on
genes (nature), but also on the environment (nurture). It is usually the “joint product of genes and
environment”, one of the first principles in Leda Cosmides and John Tooby in “Evolutionary
Psychology: Nature and Nurture” (attached). This remains our group’s thesis.
Introduction
Take for example this Calvin and Hobbes strip.
We assume that duplication is the same as cloning and therefore the two Calvins are
genetically similar. Hobbes (that is the tiger) implies in the last frame that the two are similar in
behaviour. Ignoring the absurdity, it brings us to a question: Do genetically similar people
behave the same way? That is, can nature alone determine how one behaves?
This seems quite impossible. Take another fictitious, but thought-provoking, example in
Mowgli, from “The Jungle Book” by Rudyard Kipling. He is genetically similar to all human
beings and much less so to wolves, bears and panthers, but he behave more like the wild
animals. In this case, it is certainly clear that nature alone cannot determine human nature. The
environment makes a difference.
Behaviour genetics
Behaviour genetics is the study of the extent to which heredity (genes) influence human
behaviour. Genes are found in chromosomes which are made up of deoxyribonucleic acid
(DNA). Our DNA strand determines not only our physical characteristics (known to some
as our
genetic architecture) but also our psychological make up. The human genome project has
isolated certain genes responsible for certain behaviour traits. For example dopamine is
responsible for “risk-seeking” behaviour, as well as hyperactivity (The Economist June 1st).
Although the probability of altering genetic make-up and therefore human behaviour is
becoming closer to reality, scientists believe that there should not be “a dichotomy between
nature and nurture” (The Economist).
Behaviour genetics include twin studies, family studies and adoption studies. Adoption
studies focused on how people with different genetic make-up, brought up in a similar
environment may or may not share similar behavioural patterns and family studies on people
with the same genetic make-up. The results are not conclusive, although it is found that the
possibility of people who are genetically similar, sharing similar behavioural traits is higher.
Twin studies remain our interest. Identical twins have 100% identical genes and the same
shared-environment (same home, same parents, same siblings, etc) , and thus any differences
between them will be the non-shared environment (individual friends, own perceptions).
Fraternal twins share about 50% of their genes and the same shared-environment. Studies made
by comparing behavioural traits in these twins are once again not conclusive: about 40%