Mating Matters Podcast “Hidden Eggs”

Dr. Wendy Walsh uses science, personal interviews and examples from pop culture to reveal the secret evolutionary motivation for most every human behavior. It will help you understand yourself better. Read transcript of the episode “Hidden Eggs” below.



Concealed fertility in humans has contributed to the sexual double standard, good Dads, and strippers who make more money when they ovulate.







Dr. Wendy Walsh:         Why is it that you can’t tell when a woman is fertile? In fact, she may not even know herself. I’m Dr. Wendy Walsh. Concealed fertility in humans has contributed to the sexual double standard; good fathers and strippers who make more money when they ovulate.

This is Mating Matters!

I’m Dr. Wendy Walsh, and this is Mating Matters. A podcast that looks at human behavior through a very sexy lens. You should know that I’m obsessed with the science of relationships. Understanding the biological, psychological, and social pressures on people makes me enjoy life more. It makes me more understanding, more forgiving, more compassionate to others and myself. And I want you to see life in the same technicolor version that I do.

You know even when we’re not thinking about sex, our ancient programming makes us respond to reproductive cues that impact just about every decision we make. We are wired to reproduce. In today’s episode of Mating Matters – Hidden Eggs, we ask the question, why did humans evolve to have concealed fertility? All that means is, no one knows for sure which magical three days each month a woman can become pregnant, and most of the time not even the woman. So, how does this impact the way we relate to each other?

Well, why don’t we start at the beginning, in the delivery room. It is usually the happiest moment in a couple’s life. For men, it’s the culmination of the arduous task of finding a date, girlfriend or wife, getting her to mate with you and hanging around for nine whole months while female hormones rule the roost.

For women, it’s the sometimes dangerous journey of finding a healthy mate who might even hang around for a few years. If you’ve ever been a single woman on dating sites, you know how hard this is. But then, it gets physically challenging. Nine months of pregnancy that might include morning sickness, bed rest and crying jags that make PMS look mild.

And then, there’s labor and delivery.

Female:            If I had to go through this a hundred years ago, I don’t know how I would have done it without the help of my doctors and my nurses and my partner to get through it.

Dr. Wendy Walsh:         Ouch! But after all that women go through; the pregnancy, the labor, the delivery, at least they’re left with one reassuring fact. There’s no doubt who the mother is. But the father? Men can never be too sure. That’s because human females have concealed fertility, approximately three days in a month when women in their childbearing years can become pregnant. And even women aren’t aware of when these three days come. Could it be that his sperm reached the egg during that mysterious window of ovulation? Could he be sure that no other man gained access during that month?

You know, sperm are survivors. They can live in a woman’s vagina for five days waiting for the egg to arrive or standing ready to encounter another man’s fighter sperm. Those are the fastest swimmers. They’re ejaculated first with the sole mission to kill any lingering men sperm.

So who won? Which guy is actually the father?

Female:            He makes these really cute faces sometimes that remind me of my husband.

Dr. Wendy Walsh:         It’s the chant of new mothers everywhere. If you ask any postpartum mother who she thinks the baby looks most like, she’s far more likely to say daddy instead of mummy, no matter what the baby looks like. It’s always been speculated that this worldwide female behavior evolved to elicit care and protection from a man who might not be certain about his paternity.

Now, there’s new research to show this actually works. Professor of Economics at Binghamton University, Solomon Polachek and his partner Marlon Tracey from Southern Illinois University, studied 456 couples. Now, these couples were not married, nor were they living in the same home. These are called “fragile families”. What they found was interesting. When the baby looked like the father, the child was healthier one year later. And that’s not always because of hardier male genes. The researchers say that if a father believed the child looked like him, he actually spent two and a half more days a month caring for his child and checking in, assessing the economic needs. You see men invest more if they believe a child is actually theirs. And really, does a newborn look like anyone?

Male:               When they were born, they both look like me. Weirdly enough, my older son, when he was about five, looked identical to my wife, like there was some kind of weird shift. And my younger son looks identical to my father. Like people always say, “He looks like your father,” which he should look more like me. Right?

Dr. Wendy Walsh:         Having concealed fertility isn’t common in all primates. Take rhesus monkeys for example, how do they spot a fertile female? It’s all in the face reading.

Researcher James Higham of the German Primate Center in Gottingen, Germany found that when a female rhesus monkey is ovulating, her facial features change, ever so slightly. And 85% of the males can see the difference. But there’s a catch, only if he knows her well. In order to pick up the subtle cues about fertility, male rhesus monkeys need to become friends first. Males who spend time getting to know females tend to pick up on sexual signals much better. Hmm, gives new meaning to friends with benefits.

For baboons, no mind reading or facial decoding needed at all. One of the most conspicuous of all signals of primate fertility is the large swellings displayed by female baboons. The Amboseli Baboon Project in East Africa is one of the longest running studies of wild primates in the world. Researchers there, have been studying baboons for more than four decades. Specifically, they have studied the range and size of female well, butt, vulva, labia? Let’s just call them swellings.

Look, if you were glued to National Geographic Magazine as a kid, you’ve probably seen these oversized, bright red bulging, butt lips that female baboons showcase. And biologists hypothesize that the size of a female swelling contains important information for males to know when to procreate. In fact, the scientists at the Amboseli Baboon Project found that indeed changes in swelling size within each sexual cycle, correspond with ovulation. Unless you think we humans are so different, scientists even speculate that our human preference for full lips – lip injections anyone? Or bright red lipstick are just one primate copying another.

But human beings are different. Our faces don’t change much when we’re ovulating. And as far as I know, our vulva does not balloon up like a baboon’s red butt. For the most part, men can’t consciously tell that a woman is fertile. In fact, most women can’t even tell they are ovulating, unless they have help from technology.

Female:            I have no clue when I’m ovulating. I use an app for that.

Female:            I don’t think I’ve ever really tried to track it.

Female:            The only way I know I’m ovulating is because I’m on birth control.

Dr. Wendy Walsh:         Human ovulation, a state once thought to be undetectable without medical equipment or an app, actually creates a range of subtle but definitely observable behaviors. And these female behaviors are aimed at attracting the best possible mate.

For instance, researchers Barnhard Fink at the University of Gottingen, Germany along with colleagues, Benjamin Leiding and Nadine Hugill, found that women’s bodies move slightly differently when they’re fertile, and men can pick it up. In this fun study, the researchers videotaped 48 women dancing to music. Then, they had 200 men watch the videos and rate them on a scale of attractiveness. So feminist. I’m not so sure I like this hot or not game. But it does provide some interesting information.

Turns out, men rated the ovulating women more attractive. But do women notice anything different about themselves when they’re ovulating?

Female:            I don’t think I could tell if I’m fertile or not, no. I mean, maybe I’ll crave an extra cheesy pizza or something. But besides that –

Female:            I actually can’t tell when I’m ovulating.

Female:            I definitely do feel a little bit more attraction to men, a bit more feminine. Like I want to speak a little softer with them. I want to come off a little bit more sexier when I’m walking past them.

Dr. Wendy Walsh:         Wait, did she say she tries to make her voice softer and more breathy or could her voice be changing naturally when she ovulates?

Researchers, Greg Bryant and Marty Hazelton at the University of California, Los Angeles, set out to test this idea. Like all good scientists, they began with an assumption. Their assumption, that higher, more breathy voices are more attractive to men because they signal youth and fertility. After all, didn’t Marilyn Monroe’s breathy voice wow an audience and the president in 1962 with a simple rendition of happy birthday?

[Marilyn Monroe Singing 00:10:07 to 00:10:23]

Our UCLA researchers didn’t have Marilyn Monroe as a test subject, so they used female college students instead. They recorded the voices of 69 women (interesting number scientists) and gave the women hormone tests to determine where they were in their menstrual cycle. The women were all asked to say the same thing. “Hi, I’m a UCLA student.”

Then the researchers calculated how their voice was different. Turns out, women unconsciously raise their voices when they’re ovulating. Interesting. But do men pick this up?

A study that asked this question, looked at strippers. Jeff Miller, Joshua Tiber, and Brent Jordan at the University of New Mexico had to spend many arduous weeks interviewing strippers about their ovulation schedule and helping them count their money at the end of the night. Sure enough, exotic dancers who do not take the birth control pill earn more money when they’re ovulating. On average, they earn nearly $400 more per night when they’re ovulating.

What are the men picking up on? Some say it’s scent. Pheromones may signal fertility, but it could also be the conditions of an average strip club. Strip clubs tend to be loud. They tend to be dark, and strippers make the most money, not on stage, but by doing private lap dances. And how do these ladies sell their lap dances? Well, in a noisy, dark club, there’s only one way. They get real close and whisper in a customer’s ear. The dude gets a double whammy of signals, both scent and vocal tones. And if she’s ovulating, he apparently is willing to dig deeper into his pocket and pull out more money.

The list of human female behaviors that signal fertility goes on. Research has shown that during ovulation, women fantasize about sex more often. They’re more likely to wear red or pink clothing (back to copying those red monkey butts), and they’re more flirty with bad boys. Also, college girls call their fathers less.

But what about the men who can’t pick up on these signals? It’s not a perfect science. And even in the studies, some men fail. Or what about the men who women don’t often choose for reproduction?

The movie, The 40-Year-Old Virgin is every man’s worst nightmare.

[Movie Clip Playing 00:12:59 to 00:13:23]

Dr. Wendy Walsh:         To prevent such a calamity, over the centuries, men have created social systems that increase their odds that they’ll get to mate with a woman, and help to keep competitors away. You might’ve heard of one, it’s called “monogamy”. Evolutionary psychologists suggest that the only way a man could be sure that his girlfriend or wife gave birth to a baby that was his, was to block her from other men. It’s called mate guarding.

If you’ve ever dropped by your mate’s office to strike your stuff in front of a new threatening, cute coworker, you’ve practiced mate guarding. Both genders do it. By sticking to one sexual partner, monogamy, may have evolved as a form of mate guarding. Those gallivanting groups of gatherers, females with children in tow, along with sisters, aunties, and friends were constantly moving. If a dude wanted to be sure his lady was carrying an egg that he fertilized, he better stay close to her butt.

Thus, you could say that men invented monogamy. But they also invented a kind of psychological warfare to combat concealed fertility.

[Movie Clip Playing 00:14:34 to 00:14:46]

Dr. Wendy Walsh:         The movie is called “What’s Your Number?” Because even Hollywood knows that women worry about this. In fact, the fear is pervasive that a woman will be shunned by all men if she’s revealed to be promiscuous. Now, what that means in scientific terms, is that men won’t be sure if her baby is there’s. It’s called the sexual double standard. That’s a social construct that gives men points for sexual experience and gives women demerit points.

Trust me, men invented this one. It’s so psychologically crippling that women are embarrassed to reveal their number.

Female:            I don’t ask them, they don’t ask me. I don’t want to talk about it. I don’t want to know who you’ve been with. And I’m sure you don’t want to know who I’ve been with. So, let’s just avoid it.

Female:            Oh, okay. So, the sexual double standard, I think that definitely revealing your number, you think that somebody is going to judge you by it as a woman. So, I think that I probably avoid that conversation.

Female:            Yeah, I don’t think I’ve ever had a man ask me what my sexual partner number was. I think, at least, in my experience, that isn’t a question that comes up. It’s almost like don’t ask, don’t tell.

Female:            I think that they would get this alpha male mentality and say that they can’t be with a woman who’s been with other men. They can’t visualize it because it just kind of ruins the idea of her as a pristine, proper, clean woman. It just kind of ruins that idea in their head that they’ve come up with.

Female:            I think if I told a man I had a high number, that he would think that I was a slut. That would make him feel that he doesn’t owe me any kind of respect or he doesn’t owe me a quality relationship.

Dr. Wendy Walsh:         So, what’s a girl to do? On face value, the reproductive system of having concealed fertility seems pretty cray, cray. I mean, what’s the point? Men are worried about getting access to women, and then wondering if her baby’s actually theirs. And women are worried that men will totally reject them if they give access to too many men. So, why would this system have evolved? What real reproductive value does concealed fertility give?

To speculate about the answer, we look no further than our closest primate relative – chimpanzee. Chimpanzee males are dangerously brutal animals. When they come across a chimp version of a MILF, a mother I’d like to frolic with, the first thing they do is murder the baby. It’s true. Baboons and gorillas do it too. It’s very efficient, evolutionarily speaking. I mean, baby killing rubs out a competitor’s genes while bringing on ovulation in a nursing mother.

But how about human males? They don’t murder babies so often. In fact, for the most part, men are great dads to their own kids and to others.

Male:               I coach football. I volunteer a lot at the school. I mean, it’s not like direct parenting. Coaching is probably an example of close to direct parenting for at least a couple of hours. And so, you treat these kids as if they are your own. You want to make them as good as you can as football players. I like one of the other coaches says it, and I adopted it myself. He says, “My first job is to make you a better man. My second job is to make you a better football player.” And I really like that. I’m getting goosebumps right now. Man, I’m a sap. I am such a sap.

Dr. Wendy Walsh:         The end of this evolutionary story is a big score for the girls’ club. Human males maybe physically evolving to pick up sights, sounds and scent of an ovulating woman. And they may have invented the double standard to keep women from sharing her eggs with the team. Short of any paternity test, which is just a recent tool in men’s arsenal against hidden eggs. Can a man really be sure? Is the baby growing in her womb really his? What if his fighter sperm didn’t do their job? What if he got the dates wrong? What about the dude in accounting she always mentions? Her trainer? Her handyman? The milkman?

Male:               You know you have that seed of doubt. You’re waiting anxiously in the waiting room. You’re making sure you trust the doctor, all the preparation that takes place. You’re doing the breathing exercises. But that one seed of doubt that you have is not what will the baby looked like? But actually is the baby, is it really yours? Could it be somebody else’s out there?

Male:               I’d be lying if there wasn’t a part of me that was like, I would like to know. I don’t know if that’s like an animal part of me that lives inside, but it’s the God’s honest truth. I’m like, I just want to be sure, like even though it would probably destroy my entire life if there was a mistake on the test, or if I found out the truth. My life is much better to live in ignorance. But yeah, I was curious. I was definitely curious.

Dr. Wendy Walsh:         So, if a man can’t be 100% sure that the baby his wife or girlfriend is giving birth to is his, he also can’t be sure that it isn’t his. Men are wired to spread their seed around the tribe. And if human males spent time killing babies, they might’ve been killing their own genes or their family genes. The genes of their brothers or cousins.

That’s the beauty of hidden eggs. It makes human males good dads. They take care of all babies because any one of them could be theirs. So, you see, women’s intelligent bodies developed concealed fertility to increase the chances that their babies would live.

I’m Dr. Wendy Walsh. Thanks for listening to Mating Matters. Next time, we’ll be looking at the trouble with testosterone.


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