If you’re an egoist, giving a fixed portion of your income has a fixed cost (since the marginally utility of money is approximately inversely proportional to what you have) and gives you a fixed amount of prestige, or signalling or whatever. That sort of thinking is useful for maximizing inclusive genetic fitness, so it’s no surprise that we think that way.
Does it give a fixed amount of prestige/signalling/whatever? Firstly, it only does so if you’re telling the world about your giving (which, e.g., at least one of the ancient traditions featuring “tithing” strongly discourages); secondly, whether reasonably or not, I think you get more prestige from giving away 10% of what you have if you are either very poor (so that doing so really hurts) or very rich (so that it’s an impressive-sounding sum that seems like it can do a lot of good).
However, the fact that a fixed fraction of income is kinda like a fixed sacrifice of utility does seem like it might be an important piece of the picture. Somehow.
If you’re an egoist, giving a fixed portion of your income has a fixed cost (since the marginally utility of money is approximately inversely proportional to what you have) and gives you a fixed amount of prestige, or signalling or whatever. That sort of thinking is useful for maximizing inclusive genetic fitness, so it’s no surprise that we think that way.
Does it give a fixed amount of prestige/signalling/whatever? Firstly, it only does so if you’re telling the world about your giving (which, e.g., at least one of the ancient traditions featuring “tithing” strongly discourages); secondly, whether reasonably or not, I think you get more prestige from giving away 10% of what you have if you are either very poor (so that doing so really hurts) or very rich (so that it’s an impressive-sounding sum that seems like it can do a lot of good).
However, the fact that a fixed fraction of income is kinda like a fixed sacrifice of utility does seem like it might be an important piece of the picture. Somehow.