symmetry
Explanation
This comic opens with a character explaining that humans are attracted to bilateral symmetry: "It's an evolved response. Perfect bilateral symmetry is hard to fake. Nobody's left and right sides are exactly the same, so if someone is high symmetry quality of a mate, they're likely to be."
Another character then takes this to its logical extreme: "Do you mean like, you see my attractive bilateral body?" Someone responds with "What?" -- and in the final panel, a character who is perfectly bilaterally symmetrical (symmetrical face, hair, and body) approaches two people and says "Hey girl," to which they respond "So hot" and "So fuckin' hot."
The joke takes a real evolutionary biology concept -- that bilateral symmetry is indeed considered a marker of genetic fitness and is correlated with attractiveness across many species -- and pushes it to absurdity. The perfectly symmetrical person is apparently irresistible not because of conventional good looks, but purely because their left and right sides are identical. The comic exaggerates a subtle, unconscious preference into an overwhelming attraction, as if humans are helplessly drawn to symmetry like moths to a flame. The crude enthusiasm of the onlookers' reaction ("So fuckin' hot") contrasts hilariously with the dry, academic explanation that preceded it.