i don't think true selflessness exists, but i also think that is completely and utterly irrelevant.
Everything is fundamentally fueled by selfishness, but it seems to be a fundamental truth of the universe that cooperation is optimal for an individual if they can achieve it.
for example cooperation is the thing that allows us and animals like ants to be so hilariously more successful than other species, and on an ecosystem level everyone is cooperating since their chemical structures are compatible. If something were to evolve to use mirrored sugar (which is incompatible with the version of sugar molecules we use) then they'd have nothing but themselves to eat and thus promptly starve.