Indeed it can be seen as our human essence, how few behavioral imperatives we follow.
Firestone, for instance, associates sexuality with an absolute, ungendered, human essence.
Recalled sexual longings would at least make me feel we had not wasted our store of human essence needlessly.
"The human hand, the human eye, the human essence brought to focus in the awareness of one person who tested the limits."
Then the demon draws in the human essence, breathes his own into his prey.
And from that moment his human essences began to dribble away.
Later they sleep in the same bed and she imagines the stealthy return of her human essences.
This is the most basic way in which they develop and express their human essence' (see also, the quotation from Allen Wood above).
What we needed to know was that the living human essence could exist independently of the normal human biochemical machinery.
The film, investigating a similar question, pushes its characters to the very limits of their humanity even as it strips them to their human essence.