Because human beings are not programmed for it to last. Fisher’s basic premise is that lust evolved to insure procreation and the continuance of the species. Romantic love evolved to drive the couple to choose a mating partner. And attachment evolved to keep the couple together long enough to raise offspring. According to her, the brain chemistry of the three states is complex and does not always respond as one would like, but generally the hormones produced during romantic love diminish over time as the relationship changes to a more secure and stable attachment.

“Under some circumstances, dopamine and norepinephrine can stimulate the release of oxytocin and vasopressin–and contribute to one’s growing feelings of attachment. But increasing levels of oxytocin (found in both men and women) can also interfere with dopamine and norepinehrine pathways to the brain, decreasing the impact of these excitatory substances. Hence the chemistry of attachment can quell the chemistry of romance.” (pp 91-2)

This may be for the best. It isn’t practical for people to stay in a state of heightened romantic passion indefinitely; there is too much work to do, especially once there are children. Most men will probably not agree with this assessment!

topics: nature