Middle Earth does not have a single tree of common descent, but multiple acts of special creation, each of which then speciates further.
Souls are directly created by Eru for all sentient races (elves, men, dwarves, ents) and sent directly from outside creation.
Elvish languages were not gendered grammatically, but did distinguish between animate and inanimate.
That is they did not distinguish between "he" and "she", but did between "he/she" and "it".