>4) There is no known microbe which is beneficial for some humans, and harmful >for others (micro-organisms responsibles for diseases like TB or measles have no known beneficial effect). Well, you could consider that it is beneficial to be infected with measles when still a young child, because it then gives you immunity for when you become adult (if you do ;), as adult onset measles has far greater risk. >5) The only known beneficial micro-organisms are those which live in >the digestive tract (correct me if I am wrong). I have read that similar organisms are in breast milk. > -some animals are predators (harmful) > -some animals are preys (beneficial) > -some animals are neutral (not predators, not preys) > -some animals are not predators nor preys, but since they compete against >others, they help control the growth of various populations > -obviously, the weakest animals are the most likely to become victims of >predators. Predators may be harmful to some animals of a species, but they are usually beneficial to the species as a whole: ie if the numbers of a specy (?) are allowed to multiply unchecked then ultimately the food supply (eg grass) would be decimated to the point where none would survive. [ This may be the reason why lemmings commit wholesale suicide when they are in big numbers]. Regards, Lynton