I would imagine that increasing crop yields would do social good primarily via decreasing the amount of cultivated farm land, especially since we're well past Jevons paradox territory with calorie intake I imagine.
While the pharmaceutical industry is large, the marginal researcher does still seem to have a pretty positive impact from an outside view.
The most positive use of human time probably looks something like antiwar advocacy, but I don't really think that most quants have the social skills for that tbh.
to stop war we need to stop being lazy, greedy and most important: envy, which is impossible.
>While the pharmaceutical industry is large, the marginal researcher does still seem to have a pretty positive impact from an outside view.
From this outsider's point of view it's failed to have a positive impact; people nowadays are far less healthy and happy than they were half a century ago when the pharmaceutical industry barely existed.
>decreasing the amount of cultivated farm land
I have good news and bad news for you. Good news: we've known the solution to that for more than a century, which is to reduce livestock consumption, a cause which many smart people have dedicated their lives pushing vegetarian/vegan culture and producing alternatives. Bad news: from my point of view, the masses are not going to give up meat and eggs faster with each additional alternative meat.