SOUL or soul-like vehicle is not necessary for normal earthly existence.
However because we are evolving beings continually developing defenses against threats to ourselves, and death being a major threat, we must consider the possibility that over the generations we have gradually built— or are building— a non-material lifeboat to which we can transfer our awarenesses in the event our minds are destroyed.
This possible source of a soul can be quickly rejected, due to the inoperability in this case of natural selection, or survival of the fittest— a primary evolutionary ingredient.
The only improvement such a lifeboat-soul could provide would occur after death, when all connection to the material world is severed.
Since the organism would become empowered only after its earthly involvement was over, there is no way this energy could be converted to increased survivability— thus multiplicity and dissemination, with consequential continued development— in the field.
(There is a chance that awareness of such a power over death, if that were somehow possible, would translate into an increased level of courage, a mental strength, but it might also reduce fear of death, lessening the survival instinct.)
Actually, it’s fortunate for us that this is so. There’s the chance, since human development has surely yet to reach the highest level possible, that any evolved incorporeal aspect, being that much more esoteric, would likewise be less than fully developed, or even infantile.
It’s frightening to imagine the result if our consciousnesses, upon our deaths, were released to an ill-formed vehicle.
We might spend an eternity adrift in a semi-aware state, with little or no sensory input or output— perhaps the nearest thing imaginable to a literal hell.