I wrote about the literature around the evolution of virulence previously which people might find useful for finding references on the topic.
In short, it is complicated:
zoonotic diseases (like COVID) don’t follow a consistent pattern early in their evolution because they are so far removed from being adapted to humans as a niche.
As long as there is a correlation between deadly-ness and ability to reproduce, diseases will face evolutionary pressure to become more/less deadly depending on the circumstances. This is strongly influenced by transmission mode (but isn’t the only factor):
a. Disease transmitted by close person-to-person contact → disease can’t make host too sick, or host won’t come into contact with others → disease evolves to cause milder infection.
Example: HIV has relatively few effects on hosts for years before culminating in AIDS.
b. Disease transmission doesn’t require person-to-person contact → disease can optimize other features of transmission such as producing many copies and using host resources → disease evolves to cause severe infection.
Example: malaria is spread via mosquitos and doesn’t require person-to-person contact in order to spread, which might explain why it is such a debilitating disease.
Thanks for this comment, this is much better than my post. I simply wanted to address a very common misunderstanding that is repeated over and over in TV by non specialists, in a simple way. Your comment is probably much better suited for the LW audience that is normally expecting a more detailed explanation.
I wrote about the literature around the evolution of virulence previously which people might find useful for finding references on the topic.
In short, it is complicated:
zoonotic diseases (like COVID) don’t follow a consistent pattern early in their evolution because they are so far removed from being adapted to humans as a niche.
As long as there is a correlation between deadly-ness and ability to reproduce, diseases will face evolutionary pressure to become more/less deadly depending on the circumstances. This is strongly influenced by transmission mode (but isn’t the only factor):
a. Disease transmitted by close person-to-person contact → disease can’t make host too sick, or host won’t come into contact with others → disease evolves to cause milder infection.
Example: HIV has relatively few effects on hosts for years before culminating in AIDS.
b. Disease transmission doesn’t require person-to-person contact → disease can optimize other features of transmission such as producing many copies and using host resources → disease evolves to cause severe infection.
Example: malaria is spread via mosquitos and doesn’t require person-to-person contact in order to spread, which might explain why it is such a debilitating disease.
Thanks for this comment, this is much better than my post. I simply wanted to address a very common misunderstanding that is repeated over and over in TV by non specialists, in a simple way. Your comment is probably much better suited for the LW audience that is normally expecting a more detailed explanation.