- Looking at concordance rates
- If there is a high concordnace rate between M/Z twins- there may be a genetic cause.
- Most twins share same environment so to overcome this- scientists study twins who were seperated at birth- in order to seperate nature + nurture effects on behaviour.
- Whether behavioural traits are the result of nature (genetic) or nurture (environmental) factors.
- Adopted children share no genes in common with their adoptive families but share the same environment.
- They also share 50% of their genes with each other their biological parents but no longer share the same environment.
- Scientists can seperate genetic and environmental influences on behaviour by looking at similarities between adopted child and biological parents.
- Good for testing genetic causes of behaviour.
- Can isolate gentic causes from environmental ones
- Even if seperated at birth, twins shared same pre-natal environment for 9 months as they shared the womb. This could influence the child's development.
- Adoption agencies usually try and find similar families to bring up the twins who are to be seperated in order to make their developmental experiences as alike as possible.- any similar traits could be due to similar upbringings and not simply the genes that they share,
- Number of twins reared apart in minimal,so sample sizes are snakk and it may be difficult to generalise results.
- Many participants in twin and adoption studies are gathered using advertisements asking for suitable people to volunteer to take part in research.- bias in sampling, as the typle of people who would come forward to take part may be very different from those who would not.
Brain scanning techniques
MRI (Magnetic Resonance Imaging) scans
- a way of seeing a picture of the brain inside the skull just like an x-ray.
- Allows you to see the structure of the brain and therefore whether there is damage or tumours that may need treatment.
PET (Positron Emission Tomography) scans
- a way of seeing a picture of a 'working' brain.
- It can show any malfunction
- Shows an image of the activity in areas of the brain.
Use of animals
Lesion studies- damage to the brain is caused and the resulting change in behaviour is measured.
Evaluation of lesion studies using animals
- Samll animals (rats and mice) are often used for lesion studies as they are easier to 'house' and monitor during research than humans.
- Large samples can easily be bred in a short period.
- It is possible to cause a level of harm to animals that is not possible with humans, as long as the knowledge gained is likely to be of significant benefit to others.
- Animals are more likely to be naive participants.- Overal validity will be higher as there will be a truer picture of how the brain damage affects behaviour, without the problem of participants behaving differently in the experimental conditions (demand characteristics)
- Using animals rather than humans may be more expensive to the researcher as only the highest level of care is acceptable whereas humans can go home and look after themselves.
- Human and animals brains are different, so measuring the effect of brain damage on an animal's brain may not tell you anything about the effect of the same damage on a human.
Evaluation of the use of animals
- Low credibility- so many differences between animal and human behaviour.
- It is possible to create more damage to an animal brain for ethical reasons.- more extensive research can be done.
- When using animals, ethics must be considered- against ethical guidlines to cause pain or discomfort to animals in any research, unless the findings are likely to have significant benefit to humans.
- Any researcher using animals must be licenced to do so and must follow strict gov guidlines.
- The caging must mirror the animals natural environment as much as possible to reduce possible stress.
- It is possible to have more control over animals than humans as they are caged. - Can isolate animals away from any variables that could affect the findings.
- Possilbe to strictly control the environment which the animals are in so when the animal is fed if controlled by the experimenter.
The central nervous system and human behaviour
Central nervous system (CNS) is made up of the brain and the spinal chord.
The approach focuses on how the brain controls behaviour.
- The brain controls billions of nerve cells called neurons which pass informations around inside the brain.
- The neurones communicate with each other through synapses (small junctions between neurons) where neurotransmitters are released and passed from the terminal button of one neurone and the dendrite of the recieving neurone.
- Some synapses are exitatory- encourage neuron to 'fire'
- Some synapses are inhibitory- tells neuron not to 'fire'
- The decision to fire or not depends on how many excitatory and inhibitory messages the neuron receieves from its thousands of synapses.
- If the number of excittatory messages outweighs the number of inhibitory messages, it is likely to fire, and vice versa.
Genes and human behaviour
- genes are made up of DNA contained on chromosomes (found in the nuclei)
- We inherit 23 chromosomes from each parent.
- Some people believe that shared genes accounts for shared behaviour and difference in genetic make-up could account for differences in behaviour.
- Nature-nurture debate,
- Nature- the idea that our behaviour is determined by our biological make-up and is therefore beyond our control
- Nurture- the influence of the enviornment and experiences after birth on our behaviour.
- debate is over how much nature and/or nurture actually controls who or what we become.
The role of biological factors in gender development
- We all inherit 23 chromosomes from each parent.
- 22/23 determine physical appearance such as eye colour
- the final one determines gender.
- Females- final pair is XX
- Males- final pair is XY
- Y chromosome must be present for foetus to develop into a male
- Every foetus is female by default for early stages
- At 6 weeks- gonads (sex organs) develop but still no difference between males and females.
- Further on, the gonads begin to develop differently according to whether they are male or female.
- A gene in the Y chromosome called SRY produces a protein called 'testis-determining factor', which turns the developing gonads into testicles rather than ovaries.
- Y not present- foetus develops into female with full female sex organs.
- Y present- foetus develops into male and testicles develop.
- Default setting for all foetus is to develop into a female unless there is a y chromosome.
- Role of Y chromosome is to ensure that the gonads of males develop into testes rather than ovaries so that the male will then be exposed to male rather than female hormones.
- It is the exposure, before and after birth, that is responsible for the physical difference between males and females.
- Before we are born, exposure to sex hormones has an effect on the development of sex organs so that males develop testes and a penis and females develop ovaries and a vagina.
- 6 weeks into foetal development, If y present a protein hormone called H-Y antigen is released
- This encourages the development of testes whilst stopping the development of ovaries.
- For a few weeks of pre-natal development all foetus' have the same undeveloped sex organs, both male (wolffian system) and female (mullerian system). After 3 months of pre-natal development, if there has been development of testes and therefore producion of male sex hormones, the male wolffian system develops fully into male sex organs. Absence of male sex hormones will result in the full development of the mullerian system into female sex organs.
- First hormone to be released by the tests is called the anti-mullerian hormone, which prevents the further development of female sex organs.
- The testes then produce male androgens- masculinise the male foetus by stimulating the development ofmale sex organs.
- It is the absence of male hormones that leads to the development of complete female sex organs.
- refers to the extent to which each hemisphere of the brain is involved in different activities.
- Some evidence suggests that there are differences between male and females in terms or how their brain works and which hemispheres control the same behaviours.
- Most research on the influence of hormones and gender on brain development has been done on rats. Pfeiffer (1936) removed the sex organs of genetic male and female newborn rats and found that they all developed into adults with female hormone release patterns from the pituitary gland.
- Some rats had testes implanted onto them and there was a steady release of male sex hormones from the pituitary gland.- This suggests that the presence or absence of testosterone from the testes accounts for sex differences in the hypothalamus.
- If there is testosterone present in the body, the hypothalamus will tell the pituitary gland to release male hormones, if not testosteron is present, it will tell the pituitary gland to release female hormones.
- Human evidence against this- Daphne Went. Chromosomally male but has both the appearance and behaviour of a female.
- Evidence to suggest that females show less brain lateralisation for lagnuage abilities than males do. In males- left hemisphere is more active than the right during linguistic tasks. In females- bilateral activity, so damage to left side of brain is likely to result in less problems for females with linguistic abilities.
- Spatial tasks- in males- right hemisphere shows more activity, in females- bilateral.
- This evidence suggests that brain damage that only affects one hemisphere of the brain is likely to be more detrimental to males that females.
Evaluating biological approach on gender developme
- David Reimer supports argument that biological factors influence gender significantly.
- A lot of research done on animals- some scientists feel we cannot extrapolate info from animal research in order to explain human behaviour as there are too many differences. They are born shortly after conceptions so studying pre-natal development of a rat is faster and more practical.
- Pseudo-hermaphrodites- can suppot and refute the influence of biological factors on gender development. Born chromosomally one sex but appear physically and are raised as the opposite sex. Daphne Went is chromosomally male but was born female. In adulthood Daphne lives successfully as a female despite having a Y chromosome that makes her genetically male. Evidence refutes the theory as if a person has a Y chromosome they should develop male sex organes, develop male genitalia and develop brain lateralisation. The fact she has a Y chromosome but has developed in a female suggests that something else must have played a part in her gender development.
- Problems with hormones- Too much exposure to amounts of androgens can results in a masculine baby with two X chromosomes. OR a foetus with XY becomes feminised by a lack of exposure to male hormones result in female sex organs developing. These support the argument that pre-natal exposure to certain horomones determines gender development.
- Social Learning Theory- emphasises the role of observational learning and reinforcement in developing gender roles. Children observe and imitate the behavour if same-sex role models (parents) and are reinforced for showing gender-appropriate behaviour by being given praise and encouragement. Gender role is created by other and occurs due to experiences we have after birth, suggesting that biological sex plays a lesser role. However David Reimer- the biological sex of a child can have an overriding effect on their gender development.
- Combination of biology and environment- E.g. we treat a child differently depending on their gender and the way we treat the will influence how they behave in the future. When a child behaves as he is expected to do he will be praised and told he is a 'good boy' which strengthens his identity as a male. His future behaviour is therefore shaped by the way he is treated by others, which is influenced by the gender others perceive him to be, which will depend on his physical gender, which is dictated by his biology.
Normal male infant sex-reassigned as a girl (Money, 1975)
Study aimed to test the idea that gender can be learned, in a unique case study of a small boy whose penis was destroyed in an accident and who was brought up as a girl.
Aim- John Money believed that gender is determined by social experinence after birth andis therefore the result of our upbringing. He believed that all children are born 'gender neutral' and are created as males or females through the way that they are brought up. He tested this theory in the case study of Bruce/Brenda.
- Bruce and Brian- identical twins.
- At 10 months they were sent for circumcision because of a problem in urinating.
- Mistake during Bruce's procedure meant that his penis was burnt almost completely off.
- Bruce's parents were unsure on how to bring Bruce up.
- They saw Dr.Money talking on TV about intersex children being brought up as either male or female.
- His argument- that the sex of a child is determined by the process of their upbringing.
- They contacted Dr.Money and they decided to bring Bruce up as a female, he was surgically castrated, his name was changed to Brenda and his parents began to dress him only in dresses and encourage him to play with dolls.
- From the age of 12, Brenda was give oestrogen to encourage female rather that male puberty. Money tracked the progress of Brenda over many years as he felt it would be invaluable to measure the development of identical twins who were being brought up into different gender roles.
Analysis of Money's study
- Dr.Money believed she was all right, but Brenda's transition to 'femalehood' was not easy and she was often described as having very masculine traits. She liked to play with guns and other boys toys. She was described as a tomboy.
- Brenda even urinated standing up even without a penis.
- She had many behavioural and emotional difficulties throughout her childhood and at the age of 15 was so unhappy about being raised as a girl that the decision was made to allow her to live as a boy. 'David' had a penis created.
- He became much happier and in his 20's he later married and became a stepfather.
- In his late 30's David's twin, Brian commited suicide and David blamed himself for this because of the trauma that this case had caused the family during their childhood.
- He became increasingly withdrawn and unhappy which led to the breakdown of his marriage.
- His depression worsened and at the age of 38, David shot himself
- It had been argued that the strong, natural force he felt telling him that he was male, being the overriden by the upbringing he receieved, was a significant factor in the depression leading to his suicide.
Conclusion- While Dr. Money wanted to try and prove that biological gender can be easily overwritten by the upbringing of a child, he seems to have actually supported the counter-argument that biological gender is more determinate if the child's sex role.
Evaluating the study
- Dr. Money originally used the case study to support his theory that gender is determined by socially-learned factors rather that by biology.
- David said throughout his life he felt strongly that he should be male.
- Ethics- negative effects of David's case study on his life are huge, as many people believe that the stress put on the family wasa significant factor in both twins' suicides.
- There is some argument over the decision to raise Brenda as a female simply because of the damage to the penis.
- Some questions over ethical treatment of the twins by Dr.Money as he showed them sexually- explicit material to try and strengthen their gender identities.
- It was possible to compare the behaviour of twins who share the same genetic make-up but have different experiences of being brought up as either male or female. = a good matched control to compare 'Brenda's' behaviour with after her upbringing as a female. The fact that both boys developed as males even after having different upbringings provides strong support for the argument that gender is determined by genetic or biological rather than social factors.
Gottesman and Shields (1966)
Aim- To investigate the relationship between genetic make-up and schizophrenia, by looking at whether the twins of schizophrenics are also likely to develop the disorder.
- Studied both identical and fraternal twins wereat least one of the twin pair had been hospitalised and diagnosed with schizophrenia.
- They found that identical twins of schizophrenics had a high incidence of schizophrenia and almost three quarters of them were thought to have some kind of abnormal behaviour.
- The rate of schizophrenia in fraternal twins of schizophrenics was lower than for identical twins, but was still higher than in the general public.
- Researchers concluded that there appears to be a genetic component in the cause of schizophrenia and that, while the evidence may not suggest that genes are the only cause of schizophrenia , they may be an important factor.
- Problems- twins share at least some environments for some time, even if just pre-natal, things that happen in any shared environment may affect their behaviour.
- This research is important in the study of the causes of schizophrenia as it was part of the early investigations into a biological cause. It led to our modern understanding of the disorder and the very successful treatments that have been developed to help control its symptoms.
Is autism an 'extreme male brain' condition?
- developmental disorder which affects a child's ability to interact and build relationships with others, including parents.
- Not usually diagnosed until the age of 3/4 years, but autism is thought to be present from birth and many parents of autistic children report noticing problems with the child well before an official diagnosis is made.
- Symptoms include- lower than normal language abilities, low levels of imaginative thinking, problems with communicating and building social relationships, a preference for order and organisation, a resistance to change.
- About three quarters of all autistic people are male.- predominantly male condition.
- Baran-Cohen et al. suggested that the brain structure of an autistic person is an 'exaggeration' of normal male brains structure.
- They argue that there are many similarities between brain structure of an autistic person and the brain structure of a normal male, and that in the autistic person the brain structure is a more extreme version of the male brain.
Explaining the Issue
Male structure is different to female brain struture
- The normal male brain is heavier than a females and a brain of an autistic person is even heavier.
- Male brains grow more quickly that female brains during early development. Early growth is even more rapid in autistic people.
- Normal males have a smaller corpus callsoum than females and autistic people have an even smaller one.
Male brain function is different from femal brain function
- Males are generally stronger at spatial tasks than females and tests with autistic people have shown they're even better.
- Males develop language more slowly than females and people with autism, even slower.
Male hormones affect development
- 3 times more males that females with autism
- Males have more exposure to male hormones than females do. Females are still exposed to a small amount of male hormones from the adrenal glands so there is still some possibility of male brain structure in females. This would account for some females developing autism.
Autism may be genetic
- Research using twins has found a strong concordance rate of 60-90% for autism in MZ twins but only 5% in DZ.
Autism may be a result of other biological causes
- Some evidence to suggest that autism could be the result of damage caused by undiagnosed PKU in some cases. A build-up of phenylanine in the body prevents normal brain development so if PKU is undiagnosed it could result in abonormal brain development.