[ThrustVectoring]

I feel like the causality is likely backwards from the title - if you are less vulnerable to disease, you can better afford to boldly take risks and explore new situations and withstand the possible negative consequences.

[duskwuff]

Or: Dogs who are congenitally more prone to disease are more likely to have missed socialization windows due to illness, making them less outgoing.

[dmos62]

That would presuppose that the dog knows that he has a fit immune system, which we couldn't really explain either. I think the causality relationship is less interesting than that there's a correlation between different aspects of interaction with the environment. Maybe the causality works both ways even?

[trhway]

>That would presuppose that the dog knows that he has a fit immune system, which we couldn't really explain either.

feeling well is a pretty good proxy for a well working immune system, and it doesn't require any knowledge about immune system.