ABNORMALITY IS CAUSED BY PHYSICAL FACTORS - The biological model assumes that all mental disorders are related to some change in the body. Mental disorders are like physical disorders, i.e they are illnesses. Such changes or illnesses may be caused by one of four possible factors: genes. biochemistry, neuroanatomy and viral infection.
GENTIC INHERITANCE - Abnormalities in brain anatomy or chemistry are sometimes the result of GENETIC INHERITANCE, and so are passed from mother to child. One way of inverstigating this possibility is by studying twins. Pairs of identical twins can be compared to see whether, when one twin has a disorder, the other has it as well. This provides us with a concordance rate - the extent to which two individuals are similar to each other in terms of particular trait. There are low concordance rates for some mental disorders (e.g. phobias) but relatively high concordance rates for others (e.g. schizophrenia). Many of the genes responsible for adnormal behaviour are the products of evolutionary adaptations in our ancestors, despite the fact these traits are no longer…