72,000 nadis (energy pathways) – Myth or Reality?

I was told during my First Degree Reiki class way back in 1996 that the life force or Pranas as it is commonly known flows along 72,000 fixed pathways (also called as nadis or channels) in all human beings. This, I was told had been mentioned in the ancient texts – the shastras – and therefore could not be questioned. I just accepted this bit of information as being the holy truth and something that could not be questioned as no evidence existed to either confirm or deny it.