Women's hormones contain a hidden "intelligence" that women can use to make the best decisions in their lives — decisions that will help them to choose mates, avoid danger, compete with female rivals and produce healthy children, said Haselton, a UCLA professor of psychology and communication studies.

"Female hormonal intelligence evolved to start early — and last a lifetime," Haselton writes. Women's hormone cycles embody half a billion years of evolutionary wisdom. She has argued against what she calls the centuries-old stereotype that hormonal conditions such as premenstrual syndrome, or PMS, and menopause are problems to be "fixed" or illnesses to be "cured."

Haselton described women as "undercover ovulators." "It's not just the ovulatory phase that is concealed across the cycle, and across a woman's lifetime," she writes.

"It is every phase. No one can look at a woman and discern if she's menstruating or has PMS, or even tell — at least in the early stages — if she is pregnant or menopausal, and that is all to her advantage. Women have evolved to protect themselves from unwanted aggressions, male and female."

Haselton untangles myth from reality and offers many insights about women's hormonal cycles from puberty to menopause. Among her insights:

  1. Ovulating women tend to socialize more, are open to meeting more men, dance in ways that are rated in studies as more attractive, walk more, eat less, and flirt more than they do at other times.
  2. Beginning in 2006, Haselton began publishing research showing that women alter their behavior during "peak fertility." Their voices often rise to a higher pitch, they often dress in more attractive clothing and their body odors are more attractive to men, she found. Haselton's research shows that women feel more physically attractive when they are at peak fertility.
  3. Fertile women are more attracted to men with symmetrical features. In earlier times, male symmetry was likely to be a sign of strong genetic material, which a woman could pass on to her children.
  4. The human female in industrialized societies ovulates and menstruates more than any other species by far — about 400 cycles over a woman's average lifespan.
  5. "Menstrual synchrony" — the idea that women living together synchronize their ovulation cycle phases — is probably incorrect. Normal ovulation cycles among a group of women can easily overlap — and appear to converge when in reality they do not, Haselton writes.
  6. It's also a myth that there is any connection between the moon and a woman's ovulation cycle. "It's not the moon calling the shots — it's your hormones and your brain," Haselton writes.
  7. Estrogen is the "Iron Lady of hormones, the fuel for the feminine engine." Haselton writes that estrogen plays a role in curves in the body; high levels of estrogen contribute to the "classic hourglass figure." Women with high levels of estrogen report they are more open to a sexual affair, and feel somewhat less committed to their partners.
  8. Rates of female infidelity in Western populations are estimated to be between 20-50%. Women who have affairs tend to go for the sexy, "good genes" guys.

"We need to better understand how hormones affect our health and feelings of well-being," Haselton writes.