LSAT 120, Section 2, RC Passage 4, Pathogens

RC Passage 4 Explanation

PASSAGE TEXT: Until recently, biologists were unable to explain the fact that pathogens— disease-causing parasites— …

Paragraph Summaries

1. Scientists used to think parasites eventually evolve to stop harming their hosts because they depend on the host’s survival. A newer view suggests that some pathogens can still succeed by making hosts very sick or even killing them if doing so helps the pathogen spread to more new hosts.
2. How harmful a pathogen becomes depends on how it spreads. Pathogens that spread through direct contact, like the common cold, usually cannot afford to make hosts too sick because a weakened host may not interact with others and the pathogen cannot spread.
3. Pathogens spread by vectors, like mosquitoes, can be much more harmful because they do not depend on the host moving around. A mosquito can pick up a large amount of the pathogen from a severely sick host and spread it to someone else, allowing highly aggressive pathogens to succeed.
4. Most vector-borne diseases are highly dangerous, but some directly transmitted diseases can also be extremely deadly. These “sit and wait” pathogens survive outside the body for long periods, allowing them to spread later without needing a vector, which makes them especially threatening.

Analysis

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