Nature Versus Nurture

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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.


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% of the variance in these traits are genetic, 35% non-shared environment and 5% shared environment. ("The Nature/Nurture Controversy, Frank Fujita. Attached)

The chances of similar genes creating similar behaviour is never 100 percent. The one thing that can be concluded, therefore, is that it takes a combination of nature and nurture to create behavioural patterns as adherent to our thesis. To make it more evident that nature alone cannot determine human behaviour, we look into group behaviour.

Group Behaviour: a biological mystery

We learn in history, that in Nazi Germany, the Germans were almost totally indoctrinated. They were often...
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