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Editor's Notes

• #2: some psychologists might look at a schizophrenic’s early childhood experiences in order to explain their illness, a bio-psychologist might look at genetic factors or physiological factors (for example the presence of certain chemicals in the brain.
• #3: Darwin’s theory of evolution, suggests that all living things (including humans) have evolved from the simpler forms of life that preceded them, through the processes of sexual reproduction and natural selection or “survival of the fittest’’.
• #4: When two animals reproduce sexually their offspring acquires 50% of its genes from the mother, and 50% from the father. Genes are the individual units of DNA (deoxyribonucleic acid) which pass on specific characteristics (for example, brown eyes, curly hair etc.) from parents to their offspring. When the genes from the male and the female parents combine together at the moment of conception they do so in an essentially random way, which means that the offspring will have a unique set of genes.
• #5: This means that the offspring will possess characteristics which are different from those of the parents. Some of these characteristics may be helpful to its survival in the environment in which it finds itself. Some psychologists believe that as well as influencing biological characteristics, inherited genes may also affect human psychological characteristics. For example, it has been suggested that human intelligence is genetically determined, as is the mental disorder known as schizophrenia.
• #6: One way to investigate these claims is through twin studies. Identical twins (technically known as monozygotic or MZ twins) develop from the same fertilised egg, which splits at conception to produce two individuals with the same genetic make-up.
• #7: Fraternal (or dizygotic or DZ) twins develop from two separately fertilised eggs and are not genetically identical. Therefore if characteristics like intelligence or schizophrenia were genetically determined, then one would expect to find that MZ twins were more similar regarding these characteristics than DZ twins.