When I was younger I adopted, with my mom’s help, a golden lion tamarin at London Zoo. I don’t remember the details, but the cost wasn’t ruinous to us. In exchange, I got the satisfaction of knowing that a little ginger monkey in Regent’s Park slept more comfortably at night.

It was a strange gesture, in hindsight. There is no way our puny contribution paid for the whole upkeep of this monkey. Not with central London prices. Still, at least it was a gesture in the right direction. Like sponsoring a donkey or “buying” a bit of rainforest or a stretch of sea, those who give a small contribution to the tamarins are supporting a good cause, however remotely. The money might not be enough, but it goes to the right place.¹

At the other end of the spectrum are the truly h...