Increases in testosterone and estrogen likely drive psychological changes related to sexual passion and desire to mate, with a bidirectional interaction between hormones and psychology.

“And we now know there were increases in testosterone and estrogen, which of course could be driving the psychological changes, although I'm sure that those interact in both directions, meaning the hormones no doubt affect psychology and no doubt the psychology, these changes in passionate feelings, no doubt also increased or changed the hormone levels as well.”