Edexcel A (SNAB) A Level Biology:复习笔记8.2.10 Nature vs Nurture in Brain Development

• Brain development refers to the growth of the brain and the formation of connections between neurones, or neural pathways
• There are a number of factors that can be measured to determine brain development
  • Brain size
  • Number of neurones
  • The level at which the brain is functioning
• Brain development is influenced by both genetic and environmental factors
  • The impact of genetic factors can be referred to as the impact of 'nature' on development while the impact of environmental factors can be referred to that of 'nurture'
• It is very difficult to determine which of nature or nurture has the greatest influence on brain development
  • The genes and environment of an organism interact with each other and it is difficult to separate out the impacts of each
    • A scientist would have to completely remove the influence of one of the factors in order to investigate the other; an almost impossible task!
  • There are many different genes and environmental factors to investigate

Methods for investigating the effects of nature & nurture

• Animal experiments
  • Scientists study the effects that different environments have on the brain development of individuals of the same species
    • The environment in which animals live can be manipulated to allow the investigation of the impact of environment on brain development
      • Animals of the same species would have similar genes, therefore making it more likely that differences in brain development would be due to the changed environmental factors
  • Genetic modification can be used to switch off the function of a certain gene; raising genetically altered animals alongside unaltered animals in a similar environment allows the impact of genetic factors to be studied
    • Any differences observed in the brain development of the two groups would most likely be due to genetic factors
    • This type of genetic engineering is considered ethical in animals such as mice, but cannot be carried out in humans

• Twin studies
  • Identical twins are genetically identical to each other so if they are raised in different environments then any differences in brain development would be due to nurture, while similarities would be due to nature
    • E.g. the IQ scores of identical twins are very similar which implies that nature plays an important role in intelligence
  • When identical twins are raised together their environments will be very similar, so it can be very difficult to distinguish between the impacts of nature and nurture
    • Scientists will often use non-identical twins raised in a similar environment as a control group when studying identical twins raised together in the same environment
      • Non-identical twins are genetically different
    • This cancels out the effect of the environment, meaning any observable difference in brain development between the identical and non-identical twins will be likely due to nature
      • Traits that are more common in identical twins than non-identical twins are likely to be determined by largely genetic factors
      • Traits that show little difference between the pairs of twins are likely to be determined by largely environmental factors

• Cross-cultural studies
  • Different cultures provide different environmental influences on the brain development of children
  • Scientists can study the effect of this by comparing large groups of children of a similar age from different cultural backgrounds
  • Any differences in brain development are more likely to be due to nurture, whereas any similarities will more likely be due to nature

• Newborn studies
  • The environment outside the womb would not have impacted the brain development of a newborn baby
  • The level of brain development that babies are born with are therefore more likely due to nature than nurture
    • E.g. babies are born with a variety of basic abilities (e.g. crying, feeding, recognising faces) which suggests that nature plays an important role in the development of these abilities
    • They do not have the ability to speak which implies that nurture plays an important role

• Brain damage studies
  • Brain damage in adults cannot be easily repaired as the brain is fully developed, however, since a child's brain is still developing, they provide an opportunity for scientists to study the effects of brain damage on development
  • Scientists can choose a particular characteristic and then compare the development of that trait in children born with and without brain damage
    • If children born with brain damage show the development of that characteristic, then it is more likely due to nurture than nature
      • E.g. young children with brain damage to the area associated with language show a delay in language milestones when compared to children without brain damage, but they catch up to the level of children without brain damage by the age of 5, suggesting that nurture plays an important role in language development
    • If the characteristic doesn't develop in brain damaged children, it is more likely to be due to nature