To what extent does genetic inheritance influence behaviour? Use relevant research studies in your response.

        One of the most important studies in this part of the psychology is the Minnesota Twin Study. In this study the participants were normal couples of brothers and sisters, dizygotic twins brought up together, dizygotic twins brought up apart, monozygotic twins brought up together and monozygotic twins brought up apart. First of all it is necessary, to understand the results of this research, to understand what is meant by “monozygotic” and “dizygotic” twins and what is meant by “brought up together” and “brought up apart”. A monozygotic couple of twins are two people who come from a single sperm and a single egg that then divided after fertilization into two different fertilized eggs. Monozygotic twins have the same genes. A dizygotic couple of twins is instead formed by two people who come from two different eggs fertilized by two different sperms. They are, from the biological point of view, normal brothers and sisters. When it is said “brought up apart” it means that at very early age the two infants were separated and were then brought up in two different environments. “Brought up together” instead means that both children were brought up in the same environment with the same parents. After having analyzed all these different kinds of participants with about 50 hours of tests and interviews – which gave both qualitative and quantitative data being both case studies and experiments – the results were compared. The couples who were composed by dizygotic twins and brothers and sisters gave similar results which all showed some similarities and some differences between the two. The monozygotic twins brought up together almost had the same results as the tests made by one person twice. The monozygotic twins brought up apart, instead had about 70% of the same results and 30% of different results. This gave proof to the fact that 70% of the people's behaviour and mentality come from their genes.

        Another study can be thought of regarding this topic. The psychologist Dr. Hammer and his crew of researchers decided to find out if there was a particular gene that caused homosexuality in people. Mostly male homosexuals were analyzed in this study. The participants were recruited with advertisements of the research in newspapers. The people who participated to this experiment were interviewed and the researchers looked at the other homosexuals present in their families going as far behind as possible in genealogy. After analyzing the results that were found after having researched the families of 114 gay men, the researchers came to an apparent conclusion. They saw that in the family of the homosexuals' mother several other homosexuals were present, many more than in the father's side of the family. After having found this it was thought by Dr. Hammer and his crew that there possibly is a gene in the X chromosome that affects sexual preferences. Unfortunately this still isn't shown with certainty since homosexuality is a very difficult topic to analyze because of its variability. Still, this study also gives evidence to the fact that genetic inheritance affects a person's behaviour to a certain extent; even though the result is more vague than in the previously analyzed study.

        The research that was made by Dr. Hammer already shows that genes and genetic inheritance affect behaviour even though, since the difficulty in the subject, it does not give an idea of how much this is. Instead the experiment and the case studies made by the world famous Minnesota Twin Study give a more precise idea of how much of the people's behaviour is affected by genetics. The results of the research state that about 70% of one's intelligence and behaviour are caused and affected by his or her genetic inheritance, Dna and genes: so by the biological level. The rest is instead considered as caused by the environment in which one is brought up: so by the sociocultural level.