"In contrast to mourning and burial, it is the deep-seated conception that some part of a person does not vanish forever that separates us absolutely from the whole animal kingdom. No gorilla or bald-headed eagle ever had an inkling of their inner self finishing up somewhere once the proud body had collapsed into chemicals. It is only the early human mind that grew to strive against the prospect of the final annihilation of self, a hallmark rebellion that became hard-wired into, and always an essential element of, human nature. It is the incalculable antiquity of the first stirrings towards post-mortem existence that explains the enduring and universal belief in ghosts. Ghosts have waited in the wings from the beginning and have fluttered persistently as part of human cultural, religious or philosophical baggage ever since. Practically speaking, as a result, they are inexpungible."