Why Is Sex Fun Summary

1-Sentence-Summary: Why Is Sex Fun takes a humorous look at the evolution of human sex life, explaining why the way we behave sexually is often odd, but necessary for our survival.

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Why Is Sex Fun Summary

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Why Is Sex Fun was an impulse read. I read the title and thought to myself: “Yeah, why IS sex fun?”, so I clicked. Only now did I find out that this book was written by Jared Diamond, who’s also author of the famous Guns, Germs and Steel.

Here are the 3 fun things I learned:

  1. Your dog would think the way you have sex is super weird.
  2. Concealed ovulation developed so we stay monogamous.
  3. Menopause helps women live longer.

Now let’s have some fun!

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Lesson 1: Your dog thinks your sex life is super weird.

Compared to thirty million other animal species, we really are the “odd one out”. If your dog could talk, he’d probably pull you aside and tell you to get your sex life straight.

“How can you just randomly have sex on any day of the month? Even if the woman has just had her period. That’s gross!

And when you finally do get her pregnant, you STILL keep having sex. What’s that about?

Honestly, I don’t get any of this.

But the part that weirds me out the most is why you can’t just have sex in public, like any normal animal would do. What’s with all the dimmed lights, closed blinds, and secrecy?

I’m just glad I didn’t see you leave your socks on!”

Okay, that last part I made up. But even just comparing us to the 4,300 other mammal species on earth, these are still valid questions from your dog.

Whether you look at chimpanzees, wolves, lions, bears, birds, beavers, squirrels or kangaroos – they all mate only when the female is fertile, they do so wherever they want, and immediately stop having sex as soon as the female is pregnant.

Who’s the weirdo now?

Lesson 2: Concealed ovulation is what made us monogamous.

This was a big lightbulb moment for me. The reason we randomly have sex is we simply don’t know when a woman is fertile.

Unlike other mammals, women show no obvious, exterior signs that they are fertile. Baboons can spot fertility from miles away (they are the ones with the red bums), deer make sounds to signal they’re ready and fish can pair their sperm and eggs any time, since they fertilize externally.

Diamond argues that concealed ovulation developed in order to promote monogamy. A man who leaves a woman shortly after sex might potentially put his offspring in danger, in case she’s pregnant.

Furthermore, since we can have sex any time, the desire to immediately find other fertile females becomes weaker. And even if males were to take off right after sex, they wouldn’t know how to spot, new fertile females anyway.

This is likely designed by evolution to keep us together, protect our children, and help them grow up.

So yeah, monogamy is what’s up!

Lesson 3: Menopause helps women live longer lives.

The less fertile you are, the longer you live.


Shocker, right? But it makes sense. Keeping up fertility in the form of cells, sperm and going through the reproduction cycle over and over again costs the body a lot of precious resources.

Studies have found that male worms, who suffer from a mutation which causes them to produce less sperm, live longer.

The same is true for females, which is why menopause, the natural transition women go through around age 50 to become infertile, helps them live longer.

Even the most cared for zoo apes hardly live beyond 60 (Gregoire, the oldest chimp ever, died at age 66), yet the average life expectancy for women is 81 years.

Menopause helps women’s bodies remain in better condition for longer. Just think of the dangers and problems that come with being pregnant at age 39 vs. 28, for example.

This limit on fertility also helps women spend more of their energy towards their own development and the education of their children. In this way, fewer births have lead to a higher survival rate.

Imagine how important this was thousands of years ago, when the only source of knowledge were other people – the elders lived long enough to passed on everything they knew to their children and grandchildren, which ultimately let us evolve so fast.

Why Is Sex Fun Review

For this book reading a summary was perfect. Why Is Sex Fun is a book that I would never have bought, and this way I got to learn 3 cool things about a field I usually don’t occupy myself with a lot – biology.

My biggest aha-moment was in lesson 2, who could’ve guessed we came up with hidden ovulation on purpose, so to speak?

The dog story in the beginning was fun, in the book Diamond actually writes from the perspective of a dog, which I tried myself at here, so I believe the book will be a fun read as well.

This book was also further proof to me that pickup is bullshit, which is probably incredibly prejudiced, but something I believe in with all my heart.

I love to be able to learn something about being a CEO, creating habit-forming products, lifestyle design and then sex all within a week, how great is that?

Who would I recommend the Why Is Sex Fun summary to?

The 18 year old biology major in college, who really cares about her subject, the 40 year old eternal bachelor, who might console himself with biological evidence against monogamy a little too much, and anyone who owns a dog.

Last Updated on July 27, 2022

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Niklas Göke

Niklas Göke is an author and writer whose work has attracted tens of millions of readers to date. He is also the founder and CEO of Four Minute Books, a collection of over 1,000 free book summaries teaching readers 3 valuable lessons in just 4 minutes each. Born and raised in Germany, Nik also holds a Bachelor’s Degree in Business Administration & Engineering from KIT Karlsruhe and a Master’s Degree in Management & Technology from the Technical University of Munich. He lives in Munich and enjoys a great slice of salami pizza almost as much as reading — or writing — the next book — or book summary, of course!