Natural Selection.
It favors the better adapted organisms.
Answer: The means for transmission of disease-causing microorganism is provided by the direct or indirect contact.
Microorganisms can cause disease only once they are transferred to the body. The disease causing microorganisms are termed as pathogens which are transmitted by several ways such as from skin to skin, by nuclei droplets, through blood and body fluids or via air. In vector transmissions the disease is carried by the parasitic insects via animals, air borne transmission occurs when microorganisms move through air or the dust particles, droplet transmission occurs by coughing, sneezing or talking by the person who is infected while indirect transmission occurs by physical contact or by touching contaminated objects.
