The biological approach is determinist in that it sees human behaviour as governed by internal, genetic causes over which we have no control. However, we have already seen that the way in which an individual's genotype is expressed (phenotype) is heavily influenced by the environment. Not even identical twins who share the same genes look the same and think the same. Also, a purely genetic argument becomes problematic when we consider things such as crime. Could a violent criminal, for instance, really excuse their actions by claiming their behaviour was controlled by a 'crime gene'?