With reference to relevant to research studies, to what extent does genetic inheritance influence behaviour.


  • State what you are doing in the essay 
    • This essay will attempt to consider the merits or otherwise of the influence of genetic inheritance on behaviour. 
  • Outline the overarching principle 
    • According to the third principle of the biological level of analysis (BLA), behaviour is innate and inherited because it is genetically based (we are predisposed to a specific behaviour due to genetics). 
  • Describe genetics and the importance of research into genetics 
    • It is argued that people have a genetic predisposition.
    • Genes are segments of DNA inherited by the offspring from the parent.
    • Genes are considered responsible for the development of behavioural characteristics. 
    • Behavioural Genetics is the understanding of how genetics and environment contribute to individual variations in human behaviour, where the premise is that the inheritance of DNA influences behaviour.
    • It cannot be said that a single gene is responsible for a specific behaviour – but it is a building block.
    • But genetics alone does not affect behaviour 
      • Environmental factors (e.g. culture, diet) also influence the development of an organism. 
    • Genes are complex 
      • It is unlikely that a single gene is responsible for such complex behaviours as schizophrenia or depression. 
      • There is no causal relationship between a single gene and a specific behaviour.

    • It is thought that what is inherited is the gene that can lead to the development of the specific behaviour, not the behaviour itself.
      • This means that an individual may have a genetic predisposition to a behaviour but without appropriate environmental stimuli, the behaviour will not be manifested

        Don't forget to state that behaviour is bi-directional, explain.

  • Type of studies used in genetic research
    • Twin studies 
        • Used in genetic research to study the correlation between genetic inheritance and behaviour due to the common genetics shared by twins.
        • Monozygotic twins (MZT) identical - share 100% genetic material.
        • Dizygotic twins (DZT) fraternal - share 50% genetic material. 
        • It is usually further explored, by studying the twins either separated or together to make a correlation of their behaviour. 

    • Adoption studies 
      • Allow researchers to study the comparison between genetic and environmental influence on behaviour.
      • Adopted children share no genes with their adoptive parents but 50% of genes with their biological parents. 

    • Family studies 
      • Study behaviour between family members who have similar genetics to different degrees. Inheritance 

    • Outline intelligence 
      • Intelligence is an aspect of behaviour that has been studied in relation to genetics.
      • It was questioned whether intelligence was attributed to genetic or environmental factors. Intelligence is difficult to define
      • IQ tests have been developed by a French person called Binet to measure of intelligence and are used in much psychological research. 


Introduce studies into genetics 

  • Examples of studies into genetics include... 

Study 1: Bouchard and McGue (1981)


  • Conducted a meta-analysis – statistical synthesis of data that yields a quantitative summary of pooled results 
  • Reviewed 111 studies of intelligence correlations between siblings. 


  • The closer the kinship, the higher the correlation for IQ, which supports the influence of genetics on intelligence. 

Study 2: Bouchard et al. (1990) - Minnesota Twin Study


  • To determine how much of intelligence is attributed to genetics and environment. 

  • Longitudinal study 
  • Over 100 sets of MZT (monozygotic – identical twins raised together) and DZT (dizygotic – fraternal twins raised together) from around the world who were reared/raised together and apart. 
  • Researchers gave them approximately 50 hours of psychological and physiological testing. 


  • Similarity rates between MZTs reared apart was approximately 76% 
  • Bouchard determined a heritability estimate of 70% of intelligence attributed to genetics, and 30% to other factors. 

Connection of study to question 

  • This study relates to the effect of genetics on behaviour as the concordance rate between twins shows that their behaviour was affected mostly (70%) by genetics, rather than the environment, where the other 30% may be attributed to other factors in the surrounding environment. 

  • Strengths: 
    • much research has supported his findings, making them more reliable 
    • large sample of participants, making the study more externally valid than most twin studies 

  • Limitations: 

    • Bouchard used media coverage to recruit the sample 
    • No control over the frequency of contact between twins before the study
    • Bouchard assumed that the twins reared together experienced the same environment – equal environment assumption 

Study 3: Shields (1962)


  • Obtained 44 pairs of MZTs reared apart via the media 

  • They had a similar 0.77 correlation in IQ. 
  • This was very similar to that of MZTs reared together (0.76) 
  • This means that the environment had very little influence on the twins? intelligence. 
  • DZTs reared together had a significantly lower similarity in IQ (0.51) 
Connection of study to question 
  • This study supports that genetic factors have a larger influence on behaviour than environmental factors as the MZTs reared apart had a higher similarity in IQ compared to the DZTs reared together. 


  • Strengths: 
    • Similar findings have also been found by other, better-controlled studies
    • Pederson et al. (1992) studied the aging of DZTs and MZTs in Sweden.
    • Half the twins were separated before the age of one.
    • It was found that MZTs reared together had a similarity rate of 0.80 and DZT reared apart had a rate of approximately 0.32. 
    • This shows that genetics play a significant role in the similarity between twins, thus supporting Shields? findings. 

  • Limitations: 

    • Kamin (1977) argued that the MZTs spent a substantial amount of time together, suggesting that their environments were not completely different. 

  • Environmental factors such as race have also been found to have an influence on intelligence levels 

Introduce adoption studies:

-In adoption studies, the intelligence of the adopted child is correlated with the intelligence of the adoptive parent. 
-Since there is no biological link between the adoptive parent and the child, the environmental influence should be evident. 

Study 4: Scarr and Weinberg (1976)

Assumptions, aims and introduction: 

  • They focused on parents who had raised both natural and adopted children. 
  • The assumption was that all children will have similar behaviour/characteristics, having the same upbringing, and being raised in the same environment, with the same parents. 
  • Any significant differences between parent-child IQ correlations for adopted and natural children were attributed to genes. 


  • Trans-racial adoption participants who were African American children adopted by middle-class White families 

  • The researchers found no significant difference in IQ correlations. 
  • They were found to have an average IQ of 106 at the age of 7 
  • Whereas children of a similar background brought up in low income biological families had an average IQ of 97. 
  • The IQs of the adopted African American children in Scarr and Weinberg’s study was tested years later. 
  • By age 17, their IQs had dropped to 97 – same as the average for children of similar background brought up in their biological families. (Weinberg et al., 1992) 

Connection to study question

  • This finding supports the influence of the environment on behaviour, overriding the influence of genetics. 
  • This suggests that intelligence has a lot to do with the environment as well as genetics. 
  • Through this study, researchers have made a link that “an enriched environment may raise IQ in children.? 
  • However, it is also likely that there is a strong interaction between genes and the environment to produce intelligence level. 


  • Limitations: 
    • IQ of parents was unknown
      • There may have been a correlation between the IQ of the parents and the children which was unaccounted for.
    • No consideration of the selective placement of children 
      • Often adoption agencies attempt to place children into families that they are similar to 
      • This may be the cause of the concordance rate between the adopted children and their adoptive family
    • Lack of consideration for children who were adopted at a late age and may have been brought up in care
  • Weinberg et al.'s findings support the “niche picking? hypothesis proposed by Scarr and McCartney (1983)
    • Genes affect an individual’s preference for particular environments 
    • The environment then affects the development of the individual. 
    • Genetically similar people will tend to select similar environments, thus leading to similar IQ. 
    • Supported by Plomin and Petrill (1997)
      • Found concordance rates of IQ between biological parent and child increase over time 
    • It is possible that genetic predisposition influences individuals to tend towards environments that accentuate that disposition, thus leading to increased heritability throughout their lifespan.
    • The niche picking hypothesis supports the influence of genetics on IQ.


  • Genetics can influence intelligence as shown by supporting studies on influence of genetics. 
  • Scarr and Weinberg provided findings to suggest that the environmental factor of race affects intelligence 
    • Adopted children have a higher IQ correlation with the race of the adoptive family, rather than biological race.
    • However, upon later testing, the adopted children’s IQs correlated with that of biologically similar children, rather than adoptive race. 
    • Explained by niche picking (Scarr and McCartney, 1983), which supports genetic influence on intelligence. 
  • Genetic inheritance influences intelligence, and thus behaviour, to a great extent. 
    • large amount of supporting research 
    • the niche picking hypothesis refutes environmental factors 

  • Although it is important to note that the role of genetics in determining human behaviour and physical characteristics is significant, it is essential to bear in mind that although some characteristics are strongly affected by genetic inheritance, it is not a simple causal relationship, as other factors such as the environment can influence thus alter certain behaviour.