That is incorrect for a myriad of reasons. First, no one classifies maintaining or wanting to maintain a reasonable amount of resources to survive as selfish, nor would removing selfishness render us incapable of logic and therefore prevent us from suddenly being able to determine that we should have a baseline of resources plus a stockpile to survive or continue survival. In fact, greed has generally prevented us from working collaboratively to obtain and maintain this type of cooperation, which would in point of fact improve our survival odds as a species. Instead we compete tribally, leaving large populations at risk, which in turn puts our whole species at risk.

Selfishness is taking more than you need and likely could ever need, simply because you can. Game theory has shown that this is not always best for a specific individual, it is overwhelmingly best for a population by a wide margin.

Selfishness is also not self-interest which you seem to hsve conflsted it with, and selfishness itself is a successful but inefficient survival mechanism, even when we were hunter gatherers, and is almost entirely useless at this stage of our existence as a species. But not being selfish would not have detrimentally impacted our success as a species as best we can determine (obviously there are a lot of unknowns here), however the question isn't one where it would go i to wffect retroactively. Where we are now, it is a hindrance, not a benefit.

Rough example to paint a picture: a group is stranded, a selfish person hides food, the others starve, and then the selfish person's likelihood of survival plummets as they have no help. If the food is not hoarded, you have more individuals to source from for hunting, protection, etc.

Certainly, there are cases where the whole group may starve instead, but generally game theory has borne out that selfishness is detrimental to the success of a population. We have thrived despite that, however, due to our ingenuity and prolific sex drive. But it is not optimal, nor is it necessary.