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%