Crowding and Disease Virulence by David Clark PDF

By David Clark

This is the booklet model of the published book.

This aspect is an excerpt from Germs, Genes, & Civilization: How Epidemics formed Who we're Today (9780137019960) by way of David P. Clark. on hand in print and electronic formats.


Why it’s wishful considering to think that ailments will ultimately evolve into milder forms--and what the difficult fact skill for humanity.


Earlier considering held that, given time, all ailments may adapt, to develop into no worse than measles. Virulent illnesses have been rookies, no longer but tailored to organic détente with their human hosts. This wishful considering has visible advertising appeal--but it ignores the grotesque facet of either evolution and human history.

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Anyone who caught pneumonic plague could be dead within a day. From the germ’s viewpoint, this is no problem, provided humans coughed germs over and infected another victim within this time. In a crowded medieval city, this was normally the case. Toward the end of an outbreak, most of the population either was dead or had recovered and become immune. Hence, the plague became milder again as the number of available victims became fewer and farther between. The mild forms then spread to the next city, and the cycle repeated.

Some do. Indeed, the same disease may fluctuate in virulence as conditions change. The critical issue is which factors promote decreased virulence and which promote increased virulence. The two main factors are overcrowding and transmission mode. Consider again two variants of the same disease, one mild and the other virulent. If humans are closely crowded, the virulent version has the advantage: There is no need for the patient to linger for several days to pass on the germs. As long as plenty of new victims are available nearby, the best strategy is for the disease to grow as fast as possible inside the original victims, generating more germs to infect more people.

The purpose of evolution is not to make life better for humans, nor even to produce a balanced ecosystem. Indeed, the very idea that evolution has some underlying moral purpose is basically religious. Evolution is simply a mechanism by which different living things compete using various genetic strategies. Those that propagate their own kind more effectively increase in numbers, and the less efficient go extinct. Mother Nature has no maternal instincts. No absolute reason exists for why a disease should not remain virulent, nor why it should not get more virulent.

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Crowding and Disease Virulence by David Clark

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