It may mean development of pathogens that that hippo clan is resistant to but which rival hippo clans, or perhaps rival species, are not. Like “Guns, Germs, and Steel” but for hippos.

Lots of behaviours of mammals seem to assist the propagation of parasites. For example sneezing seems to have very little biological need, yet is incredibly good at distribution of airborne pathogens.

The sneeze reflex is complex, and clearly not encoded in the very small and simple viruses that trigger it.

I have a hypothesis that many undiscovered pathogens in fact have a positive impact on survival rates of their host, which is why behaviours that deliberately spread (some) pathogens are so common.

A sneeze is a like a cough in that its a mechanical way to expel blockage and foreign bodies from nasal mucous membranes that happen to be great environments for pathogens to grow.

In general parasites that kill their hosts are failures. That's why every single human pandemic has come from zoonotic parasites. It's parasites that are not adapted to humans and accidentally kill them. Generally, given enough time, they would eventually adapt and the strains that are the least harmful (sometimes even most beneficial) would win out as their hosts would do better and allow the parasites to spread more

This happened in South America with a cholera outbreak. In countries with good sanitation, strains that made their hosts sicker ended up dying out because people had to stay indoors more. So the strains that were less sever allowed people to go out and interact socially and therefore spread the cholera further.

Arguably the same thing might be happening with the Omicron variant which early data suggests is much much milder than previous variants

> Arguably the same thing might be happening with the Omicron variant which early data suggests is much much milder than previous variants

The evolutionary selection pressure that can result in weaker viral variants comes down to the fact that deadlier viral genetics die off in the corpses they create from their hosts, sometimes leaving only the weaker genetics in the hosts that didn't die. That selection pressure really isn't there for any of the COVID variants, especially with its long incubation time. The virus is free to mutate into stronger variants in the mean time.

The hippo isn't the only thing involved here though, the parasites and bacteria are too. So it may not be strictly best for the hippo, it may be best for something else that is able to influence the hippo.