In “Why We Love,” authors Helen Fisher and psychiatrist James Thomson Jr. argue that certain antidepressants could be blocking chemical pathways in the brain that were paved by evolution to help us meet and keep mates.

Selective serotonin re-uptake inhibitors (SSRIs) like Prozac, Paxil, and Zoloft already carry warnings that they can suppress the libido and interfere with sexual functioning. But Fisher and Thomson argue that the problem may cut deeper into romantic bonds. The book suggests that SSRIs have a major impact on three distinct but related brain systems humans have evolved: sex drive, romantic love, and attachment.