Speculation about pheromones in human beings
opposes the notion that we are entirely rational creatures.
The ideal of rationality is a fairly weak leg to stand on.
Certainly we are not the only animal without instincts.
The origin of chemical signaling goes back to the first animal
and is shared by all living things including bacteria.
The Traditional Chinese character for silkworm
is assumed to feature a small worm in a cacoon.
See also in The book of science:
Readings in wikipedia: