Answer: They usually run tests too see. For example, that's why they made blood tests. They take you blood from you, and run tests to see if you have a disease.
Explanation: Hope it helps!
Mutualism- Both organisms benefit from each other, for example bees and flowers, Bees help pollinate and the flowers give the bees nectar needed to make honey.
Commensalism- one organism benefits and the other stays neutral. For example, a bird and a tree, The tree gives the bird a home and the tree stays unaffected
Parasitism- One organism benefits and the other does not. For example, dogs and fleas, the fleas get to eat and the dogs get to suffer from the bites/ they can get sick.
A genetic mutation. All the others are results of external environmental factors.