Diathesis-stress is an example of nature AND nurture, as it can be interpreted as a gene or genes switched on by environmental factors. Recently it’s been suggested that being lonely and stressed could affect the expression of cancer-linked genes, triggering their action. The research has been done in the USA on rats, comparing those kept in isolation with those living in groups. The former group had over three times the frequency of breast tumours than the latter group, and their breast tumours were also more aggressive and deadly. The isolated rats also produced more stress hormones and were more reactive to stressful situations. Rats, like ourselves, are social animals and so being isolated is likely to cause stress.