Originally Posted by ralph124c
Since hippos defecate in the same waters that they live in, they must have good immune systems. It would be like humans living in a sewer.
Everything else living in a river defecates in it, too. Human body wastes cause disease because we form such dense populations. If a hunter-gatherer human population was shitting in a river it wouldn't be a big deal to the people downstream because it would be a tiny, tiny fraction of the volume of water. By contrast, there are 500 million people living in the Ganges river basin.