Evolution
According to evolutionary medicine, optimal virulence increases with horizontal transmission (between non-relatives) and decreases with vertical transmission (from parent to child). This is because the fitness of the host is bound to the fitness in vertical transmission but is not so bound in horizontal transmission.
The pathogen population can evolve once it is in the host. There are three main hypotheses about why a pathogen evolves as it does. These three models help to explain the life history strategies of parasites, including reproduction, migration within the host, virulence, etc. The three hypotheses are the Trade-Off Hypothesis, the Short-Sighted Evolution Hypothesis, and the Coincidental Evolution Hypothesis. All of these offer ultimate explanations for virulence in pathogens.
Read more about this topic: Virulence
Famous quotes containing the word evolution:
“Like Freud, Jung believes that the human mind contains archaic remnants, residues of the long history and evolution of mankind. In the unconscious, primordial “universally human images” lie dormant. Those primordial images are the most ancient, universal and “deep” thoughts of mankind. Since they embody feelings as much as thought, they are properly “thought feelings.” Where Freud postulates a mass psyche, Jung postulates a collective psyche.”
—Patrick Mullahy (b. 1912)
“Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.”
—Konrad Lorenz (1903–1989)
“The evolution of a highly destined society must be moral; it must run in the grooves of the celestial wheels.”
—Ralph Waldo Emerson (1803–1882)