|The mitochondria that produce energy in our cells were|
once free-living organisms. Diagram by Boumphreyfr
CC BY-SA 3.0
At some point people must have recognized the similarity between the social parasites that plagued them and the animal ones that they observed living off other animals. They saw this as a negative thing – a way of life to be despised, and they gave it a negative label. Little did they know that parasitism is a time honoured way of life, a very successful way of life, and something to which they owed their very existence.