Stress
Long-term, increased steroid levels have been linked to impaired immunity and illnesses such as heart disease, cancer and depression.
These chemicals would have affected the caveman just as they do us. Our macho image of 'fight or flight' stress is wrong, because being stressed isn't about a beating heart or a dry mouth. The signs are much more subtle - and they can't be tackled with a club and a spear.
Tips to identify stress symptoms
constant fatigue and irregular sleep patterns
poor concentration and short-term memory
introspection increases and is accompanied by neglect of the family and personal appearance
constant repetition of the same actions
increased irritability
But even if you don't recognise the stress-symptoms listed here, don't presume you're fit and well. Everyone's reaction is idiosyncratic, and it can be astonishingly difficult to recognise at the time.