Evolutionary psychologist Matt Rossano has theorised that religion evolved in three stages: In the pre-Upper Palaeolithic, religion was characterised by ecstatic rituals used to facilitate social bonding. Later, shamanic healing rituals developed in the Upper Palaeolithic. Finally, religious expressions developed over time to include cave art, ritual artefacts, ancestor worship and the development of myth and moral structures.[16] If this is true then the behaviour of chimpanzees witnessed by Goodall may be interpreted as similar to pre-Upper Palaeolithic Human religion.