Martyrdom of Saint Maurice and the 11,00 Martyrs by Florence Pontormo (1509-1556) (Image: Alinari/Rex Features)

WHAT is the difference between Jesus Christ and Superman? The content of religions and popular tales is often similar, but only religions have martyrs, according to an analysis of behavioural evolution published this week.

When religious leaders make costly sacrifices for their beliefs, the argument goes, these acts add credibility to their professions of faith and help their beliefs to spread. If, on the other hand, no one is willing to make a significant sacrifice for a belief then observers – even young children …