Gay germ model is suggestive of the poorly researched role that pathogens can have in some many
other areas, both in illnesses and behaviors. Indeed,
the of mode of action of Trojan Horse pathogens which rely on molecular mimicry could be responsible for many low-heritability, late-onset diseases, such as Alzheimer’s disease and cancer. Indeed, in the case of cancer, some are known to be caused by infectious agents, such as those caused by the human papilloma virus (HPV) (e.g., genitoanal cancers) and stomach cancer (apparently caused by
Helicobacter pylori). As Paul Ewald (Cochran’s co-author on the paper on this matter) explains,
as much as 80% of all cancers will turn out to be caused by infections. This would be revolutionary, if true, because it would suggest that there’s a way to fight the often highly unsuccessful war against cancer, as demonstrated by the success of the HPV vaccine.
Their paper discussed the under appreciated role of infectious agents in all manner of human diseases in great depth:
Infectious Causation of Disease: An Evolutionary Perspective (2000)
They note that infections have fallen out of favor as a possible cause of disease because infectious agents have been increasingly harder to identify – many of the easy-to-spot infectious agents have already been found. This leaves the harder to find pathogens to make up the bulk of those left to be discovered.
Indeed, their paper is very insightful, and quite chilling. They note that even many diseases with known genetic links may have infectious roots. Infectious agents may create a selective pressure favoring otherwise deleterious alleles to persist.
Their analysis breaks it down:
"One useful tool for diagnosing infectious causation can be derived from the central principle of evolutionary biology: evolutionary fitness. Estimates of the fitness costs that are attributable to a particular disease (averaged over the entire population) can be used as an indicator for assessing whether the disease could reasonably be ascribed to genetic as opposed to infectious causation. For a genetic disease to be maintained at equilibrium in a population, the loss of the allele for the disease must equal the rate at which the allele is reintroduced. If the allele does not provide a fitness benefit, the loss due to the fitness costs of the disease would need to equal the rate at which the allele is generated through mutation. This reasoning leads to the conclusion that estimates of fitness costs can provide a sense of whether the disease is attributable to something other than simple genetic causation. Any human disease with a frequency that is too high to be maintained by the mutation rate is implicated as being caused by something other than just human genes. If the disease is inherited in Mendelian ratios and is too widespread to be accounted for by founder effects or genetic drift, and if the time has been sufficient for natural selection to drive the frequencies of deleterious alleles to low levels, the allele must have conferred some compensating fitness benefit. The only such compensating fitness benefit that has been documented for major human genetic diseases is resistance to infection."
