Maybe it helps to distinguish between purpose and function? Many times we use the word purpose to merely mean function. Other times, we refer to the end goal of a sentient being, usually something arrived at via some existential narrative. (the meaning of life stuff) We act to preserve our own lives, eat, poop, reproduce, and raise more humans, but that usually is taken as a more functional (and less teleological) description. Purpose seems to come more from an individual developing a vision of what is important in their lives, both in the personal sense, and as a member of a human community.