Secrets Every Married Woman Should Know: What Penis Size Can Teach Us About Monogamy

Monday, February 10, 2014 by Meg   •   Filed under Sexuality/Relationships

We prize sharing in theory, but nowhere near the extent of our nomadic ancestors who shared food, resources and mates among them like a socialist hippie commune.The egalitarian--or equal--structure of most early nomadic societies relied on both men and women for survival. This equality--along with cooperative caretaking patterns--allowed for sexual expression that favored multiple partner mating.

In other words, we reared our children in big cooperative groups, and lifelong monogomy wasn't really a priority, or a benefit. Switching partners was the norm.  

And there is still a part of our brain that craves this.

This drive towards additional partners might be all well and good. After all, we don't act on every drive we have. But, problems arise when women are told that they aren't supposed to feel things for others once they get married, or that to do so means that something is wrong with them or their relationship. It's not as fun to have these predispositions in a society where the drive to swap mates triggers guilt or severe anxiety for women who don't recognize it as a part of our ancestral lineage. 

It doesn't mean something is wrong with you. It doesn't even mean that something is wrong with him (even if that's hard to believe sometimes). It means that we live with regulations that aren't reflective of internal drives. This means that sometimes we have to work a little harder to stick with things that don't come as easily, especially in a world of Snow White and happily ever after. 

Guess what? Your fascination with the pool boy or your sister's husband is normal. Congratulations, your brain is working properly.

In light of the most common fears that women (and some men) come into therapy with, here's what the fascination with the pool boy doesn't mean:

  • That something is wrong with you
  • That something is necessarily wrong with the relationship
  • That you are going to cheat
  • That things will never improve
  • That things with the pool boy (or whoever) will be better than the deal you have now

That last one can be hard to grasp, especially because hormones can trick people into thinking that this time will be different. You pump enough oxytocin into someone you can get them to fall in love with a brick, or an actual frog.

But the oxytocin bursts don't last forever, nor did we evolve to swap mates only twice. We evolved to do it a whole bunch of times. The pool boy probably has a good four years or so before the mailman looks enticing. 

So why would we come to have such predispositions?

Why Do People Want to Cheat?

The Evolution of Serial Monogamy and the Drive to Leave

Till death do us part? Hardly.

According to anthropologist Dr. Helen Fisher, it should be more like:
"Till the kids can walk well enough that I don't have to carry them."

Short-term pair bonding--or serial monogamy--is having a series of shorter term committed relationships, usually for the purposes of rearing a child. In Fisher's book, The Anatomy of Love1, the drive to swap mates usually happens when children are around three to four years old. At this juncture, children are more mobile, requiring less protection and carrying from their parents. Then, mothers can  seek a new partner for another pregnancy. 

Of course, lots of other things can influence this drive. For example, a new pregnancy from the same partner means a longer period of connection is beneficial to all, and the drive to separate should decrease. Not to say that people don't separate with small children, but they do so now with the knowledge that the kid will probably survive. If our ancestors could have guaranteed that, they may have broken bonds before the three year mark too.

Current American divorce statistics support the three to four year time frame. We are a nation of serial monogamy lovers. We just don't dare admit it.

But, why switch at all? Why not just have more kids with the same partner?

Evolutionary Reasons for Swapping Mates; When Monogomy Doesn't Work

Theories for mate swapping vary. Even today, chimpanzees and other primates often mate continuously with different partners during ovulation, likely to confuse paternity and make all mates less likely to harm the child. While most nomadic societies weren't killing their young, there may be something to the idea that bonds formed between the mother and multiple partners may have provided more protection overall.

Some anthropologists cite variable environments as a reason that switching partners would have been useful. Since the environments ancestral humans found themselves in differed greatly, it would have been difficult to tell which characteristics would have been most beneficial to a child living in them. Would your environment favor children with height or physical bulk? Would a genetic predisposition to have slower metabolism serve them better? It depends on where you found yourself, and by having children with different genetics, early women would have been more likely to have a child who survived to reproduction. 

It's like hedging your bets, but with children instead of poker chips. 

Sex At Dawn...and Any Other Time

Other theorists see things a little more strongly. 

"More strongly then betting with children?"

Sex At Dawn2 authors Christopher Ryan and Cacilda Jetha argue that our current expectation of lifelong monogamy is a slap in the face of evolution. Their theories center on the notion that humans were made to be highly promiscuous. According to Ryan and Jetha, there is strong physical evidence which points to a history of multiple sexual parters at once.

Physical traits that are not present in monogamous mammals:

  • Cervical deign to filter sperm of more than one partner
  • Female sexual vocalization to invite additional participants (because there has to be a darn good reason to call out and make yourself vulnerable to predators)
  • Sperm in males are aggressive and ready for inter-vaginal competition with the semen of other males (as seen in other promiscuous animals)
  • Prolonged thrusting behaviors, to suck competitor sperm away from cervix
  • The female orgasm, which can propel the semen of the one who triggers it closer to the egg
  • Large penis and testicle size of males, which is not needed (or present) in more monogamous mammals

For the record, that large penis thing might be helpful if you're really into mate swapping. Nothing butters a man up like complimenting his junk. 

"Hey baby, you know how you have that huge penis? I think that means I should be allowed to sleep with other people."

Despite all this, one cannot argue that monogamy was never beneficial to our ancestors. With a number of early environments, there were surely those that favored monogamous unions, with or without occasional adultery. Humans have clawed their way to the top of the food chain because of our ability to adapt. Sexual expression is simply one more area where that history of flexibility can come out in confusing ways.

Monogamy can be a great thing for people who choose to go that route. However, it is important that we understand our history in order to provide the context for our current drives. The drive to leave is a normal experience, and most feel its pull at some point.  By being aware of it, women may be more easily able to identify the issue and decide what action to take. This is particularly true for those who enter therapy feeling the drive to leave their spouse but without any trigger in the relationship, or a vague unidentifiable notion that something is missing. 

"We're happy together, but..."
"He really treats me well, but..."
"I love him....but..."

Instead of guilt or fear that the response is abnormal, women may benefit from normalizing this experience. It isn't just you. It's pretty much everyone, from the dawn of time and onward. Instead, feeling the pull of such a drive can be seen as an evolved way to trigger us to act, a genetic predisposition to find a way to increase bonds with someone we care about or have decided to stay with. 

For the record, nothing pushes oxytocin and bonding quite like orgasm.

Bring on the magic bullet, baby.


Humans may not have evolved to be monogamous, but we did evolve to be sexually flexible, which means monogamy can be chosen. We just have to try a little bit harder and be a little more deliberate in our approach to fostering relationships....and orgasm. 

Did I mention orgasm?


It also means you don't have to feel badly about following the pool boy with your eyes, so long as you are conscious of your relationship goals. After all, at any other point in human history, you totally would have tapped that.

Related Posts:


Topic-Relevant Resources

The Anatomy of Love
An in depth look at a history of human mating. Sex, anthropology and more sex. What more could you want?

Sex At Dawn
Exploration of modern relationships from the evolutionary perspective. Everything you ever wanted to know about male penis size.

The Woman That Never Evolved: With a New Preface and Bibliographical Updates, Revised Edition
Anthropology, wit and the evolution of the modern female.

Everything you ever wanted to know about the connections between your vagina and your brain. It's worth the read.

What Do Women Want?
An exploration of female sexuality through interviews with prominent researchers in the field, including not yet published research (at this time)