We are the only female primates that do not undergo estrus—a time when the anogenital areas turn red and swell signaling receptivity for sex. The obvious bright swellings also indicate the female is fertile. This is also referred to as sexual heat. Science is a male-dominated occupation, full of bias in assessing the role of women in evolution. Nowhere is this seen so acutely as it is in considering why human females do not undergo estrus. Many of my male counterparts see the loss of sexual heat as simply the evolution of continual receptivity that benefitted the males of our species., and others believe sexual heat still exists in more subtle ways. Some of the current thinking on the end of estrus can be summed up as follows:

Conflict among the males of a troop was diminished because there was no need to compete for females. Males benefit, females don't.

Males could now be "tricked" into pair bonding because they couldn't be sure if any offspring were theirs. Really? Any divorce lawyer can attest to the fact that we still have pair bonding issues.

Male parenting was assured. Seems to me male parenting was a 20th Century invention.

Ovulation became hidden so females could procure more meat. Our instincts were centered on prostitution.

It is probable that both males and females were gatherers in our early evolution and the basic family unit was mother and offspring with males dropping by when they were out of food or wanted sex.

The other side of the coin is that females still show signs of estrus, and have discernible sexual heat. As "proof," we are offered the following:

Women's faces undergo a softening during ovulation/heat, becoming more attractive to males. How does this work in a darkened bar, or viewed while hopping around on the dance floor?

Lap dancers make more money when ovulating. Hey! Researchers want to have fun, too.

Women do not see themselves as more attractive but males do. Low self-esteem or accurate assessment?

Men perceive fertility by a change in a woman's sexual secretions. Exactly what is he up to down there? If we can't tell, how can he? Perhaps he has a microscope.

The armpits smell better during ovulation, acting as a pheromone. HUH!?

It seems the signs are so subtle, we can't perceive them, but the indomitable male can. There has to be more to the fact that women today ovulate in secrecy. To understand this, we have to go back to the beginning to the LCA, or Last Common Ancestor of apes and humans. The divergence began some 6-8 million years ago. We see apes and other primates as they exist TODAY. They have also been evolving for 6-8 million years. Estrus evolved one way for them, and another for us. What we see today is not what existed then. Chances are the LCA had a very moderate estrus. After all, even back then it appears we walked on two legs. A hugely swollen anogenital area would have interfered with basic locomotion. Of course, we could have evolved a big red nose as a signal of fertility, but we didn't.

At some point, we became cognizant enough to make a connection between sex and pregnancy. Females may have chosen to hide during the time they went into heat. They may have tried to avoid pregnancy to better space children. Females could wash off a scent that carried to males. The ones who were most successful at hiding ovulation were able to devote more time and effort into the offspring they chose to conceive. Evolution favors good child rearing practices and mothers who could hide estrus were more successful and passed the ability to hide estrus further down the generations until it disappeared. Even today, unplanned pregnancies can cause astronomical problems for women. Poverty, genetic issues, social stigma, and other problems plague various cultures. In industrialized countries, we have ways of dealing with unplanned pregnancies, but what recourse did early females have? Evolution would have favored hidden ovulation if it meant the offspring born grew up stronger and healthier than heat-encumbered females. However, the ultimate goal of evolution is procreation, so nature threw in a caveat. Eventually, females didn't have to hide heat. But it became hidden from ourselves! We became vulnerable to pregnancy again.