Chapter 7: Sex and Reproduction

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You know that feeling?

Life just keeps throwing things at you, the deadlines, all the responsibilities, just that constant pressure.

Well, our bodies respond to that stress in some really profound ways.

And today we're diving into one of the most intimate areas, how it messes with our sex lives, and even our ability to reproduce.

Yeah, and it's way more than just, you know, not being in the mood.

We're talking deep physiological shifts, things that actually reroute hormones, disrupt cycles.

They can even impact the basic mechanics of conception.

Welcome to the deep dive.

This is where we pull out the most important nuggets of knowledge from the source material for you.

And today we're looking at Chapter 7, Sex and Reproduction, from Robert Sapolsky's, well, really groundbreaking book, Why Zebras Don't Get Ulcers.

So our mission here is to unpack how stress tangles things up for both male and female reproductive systems.

We'll get into hormones, desire,

even the really complex topic of miscarriages.

We want to make all these biological processes easy for you to imagine, you know, without needing any diagrams or charts.

Just the essentials.

We're going to uncover some surprising facts, some real world examples that honestly might just change how you think about stress and intimacy.

So we'll kick off with the guy's male reproductive hormones, the mechanics of erections, and then we'll shift over to the female system,

cycles, libido, miscarriage.

Yeah, get ready for some maybe unexpected insights.

This chapter really shows just how deeply intertwined our stress response is with these, like, fundamental parts of life.

OK, let's start with the male system.

It seems like there's this hidden vulnerability, you know, a complex biological dance that stress can just trip up really fast.

So when things are running smoothly, no stress.

How does it normally work?

Testosterone, sperm creation.

Right.

Think of it like a chain of command starting up in the brain.

You've got the hypothalamus and it releases LHRH.

That's luteinizing hormone, releasing hormone, kind of the initial go signal.

OK, the first domino.

Exactly.

Then LHRH tells the pituitary gland, you know, the body's master gland, to release two more hormones.

LH, luteinizing hormone, and FSH, follicle stimulating hormone.

So brain signals pituitary.

What's next?

Well, LH travels down and tells the testes, OK, make testosterone.

That's your main male sex hormone.

Right.

And FSH, the other one, that's responsible for the actual production of sperm.

So it's this relay.

Brain -casting pituitary saties result testosterone of sperm.

That's your standard issue, unstressed male setup.

And then stress walks in.

What happens to this well -oiled machine?

Ah, yeah.

That's where it gets really interesting and frankly kind of disruptive.

When stress hits, the whole system gets inhibited, like the brakes get slammed on.

How so?

Well, LHRH concentrations from the hypothalamus start to drop.

And then pretty quickly, LH and FSH levels from the pituitary follow suit.

And the direct result,

less testosterone circulating in the system.

Stress basically dampens the signal at every step.

The book gives some pretty dramatic examples, doesn't it?

Like surgical incisions, big injuries, illness, even starvation.

Oh, absolutely.

Major physical stress.

Within seconds, literally seconds of a surgical incision, that reproductive axis starts shutting down.

Testosterone plummets.

Wow.

Seconds.

Yeah.

But it's not just the big physical stuff.

Subtle psychological stress, just as disruptive.

You see it in primates.

A monkey drops in social rank.

His testosterone levels plunge.

And in humans, too.

Yep.

Stressful learning tasks in humans or monkeys show the same effect.

The officer candidate school study in the book really drives this home.

These trainees, under immense physical and psychological stress, they had significantly lower testosterone.

Right.

They had to collect urine samples under all that pressure.

And suppose he makes the point, their levels didn't drop to the levels found in cherubic babies, but it was a significant hit.

Definitely shows the impact.

So why does this happen?

What are the actual mechanisms?

OK, so there are a few things going on.

First, up in the brain, stress triggers the release of endorphins and encephalins.

These are the same things that give you a runner's high, right?

Yeah.

But here, they actually block the release of that initial LHRH signal from the hypothalamus.

Huh.

So too much of a good thing, like really excessive exercise, can backfire.

Exactly.

Too many endorphins flooding the system can suppress male reproduction.

Less LHRH means less LH, less testosterone.

Eventually smaller tests, less mobile sperm.

It's not about just being active.

It's pushing way past the optimal point.

That idea of an optimal point seems really important in physiology.

It really is.

Sapolsky emphasizes it.

Just because more of something is better, a lot more of something isn't necessarily a lot better.

Too much can be as bad as too little.

It applies everywhere.

He uses that example of extreme long distance runners, right?

Running 40, 50 miles a week.

Yeah, these 30 -year -old athletes whose skeletons can end up looking like those of 70 -year -olds?

Major bone decalcification, higher risk of fractures.

They've blown way past the point where exercise helps bone mass.

It makes sense from an evolutionary view too.

Running a marathon daily wasn't exactly leisure for our ancestors.

Not at all.

It meant you were fleeing serious danger or desperately trying to find food.

Extreme stress.

Our bodies just aren't built for that kind of self -imposed chronic extreme.

OK, so endorphins block LHRH release from the brain.

What else?

Well, stress also messes with the pituitary directly.

There's another hormone, prolactin, which also gets released during major stress.

And prolactin actually makes the pituitary less sensitive to whatever LHRH does get released.

Ah, so it's like a double whammy.

Less signal coming from the brain, and the pituitary isn't listening as well.

Precisely.

And then there's a third hit right down at the test themselves.

Glucocorticoids, your classic stress hormones, like cortisol, they directly block the testes' ability to respond to LH.

So even if some LH gets through all that, the testes still can't fully do their job.

Right.

They're being told, make testosterone.

But the glucocorticoids are basically interfering with their ability to follow orders.

You see this in serious athletes too.

Often high glucocorticoid levels adding to their reproductive issues.

OK, that covers the hormone side, the testosterone production.

But what about the other crucial part, erections?

That's a whole different system, isn't it?

It is, yeah.

Very different mechanism.

Getting an erection relies mainly on the parasympathetic nervous system.

Think rest and digest, calm, relaxed state.

This system increases blood flow into the penis and clamps down on the exit route, making it stiffen.

It's a hemodynamic thing all about blood flow.

OK, parasympathetic for go.

What about ejaculation?

That involves a shift away from parasympathetic dominance over to the sympathetic nervous system, your fight or flight system.

OK, so it's this delicate balance, almost opposing systems.

And stress being the ultimate fight or flight trigger, that must really throw a wrench in the works for the erection part.

Oh, absolutely.

If you're anxious or nervous activating that sympathetic system, it's really hard to get the parasympathetic system dominant enough to start an erection.

That's your classic psychogenic impotency.

Right.

Makes sense.

And then if you do have an erection, but something suddenly makes you worried or stressed, your system can flip over to sympathetic dominance much faster than you'd want, leading to premature ejaculation.

And this is common, right?

The book says over half of visits for male reproductive dysfunction are psychogenic, stress -induced.

Yeah, more than half.

It's not usually an underlying physical disease.

It's the stress response interfering, which leads to that quirky diagnostic trick Sapolsky mentions.

The REM sleep thing.

Exactly.

Turns out human males naturally get erections during REM sleep, the dream stage.

So doctors can figure out if impotence is psychogenic or organic.

Ow.

They can have the man wear this little cuff around the penis overnight, hooked up to a pressure transducer.

If it registers pressure changes during REM sleep, bingo, the plumbing works fine.

The problem is likely stress when awake.

And the low -tech version, postage stamps.

Ah, yeah.

Tape a ring of postage stamps around the base.

If they're torn in the morning, it means there was an erection during REM sleep.

Again, suggest the issue is psychological, not physical.

That's wild.

It really shows how powerfully stress can just shut down that response.

Yeah.

You know, the book makes the point that problems with erections are often more immediately disruptive than low testosterone.

Yeah, because even with lower testosterone and sperm count, things might still sort of muddle through reproductively.

But no erection.

Game over, basically.

Forget about it.

This sensitivity is seen across so many species.

But then, you prepared me for this, the hyena exception.

This just flips everything on its head.

It's such a great example.

It really underscores how specific our normative physiology is.

So the spotted hyena, often totally misrepresented as just a scavenger, but Sapolsky points out they're actually fabulous hunters.

And their social structure is totally different.

Females are dominant.

Dominant, more muscular, more aggressive, even have higher levels of androstidiomy, which is related to male sex hormones.

And the physical side is bizarre, too.

Females look like males externally.

Pretty much.

Females have what looks like a scrotal sack, it's fake, and an enlarged clitoris that's actually erectile.

They use it for sex, even for giving birth.

It's so confusing that Aristotle apparently thought they were hermaphrodites.

Okay, okay, but here's the kicker, right?

The erection part.

Yes.

So in most social mammals we know, including us, an erection is often a sign of dominance, or at least readiness.

In hyenas, it's the exact opposite.

An erection is a sign of social subordinates.

You're kidding.

So a male hyena gets threatened by a dominant female, and he gets an erection.

Precisely.

It's like him saying, hey look, I'm just a lowly male, I'm no threat, please don't hurt me.

And low -ranking females do the same thing, they show submission with clitoral erections.

Wow.

So for hyenas, stress actually causes erections.

Seems like it.

Which means their whole autonomic nervous system wiring for erectile function must be completely backwards compared to ours.

It's a fantastic biological counter example.

Really makes you appreciate how specific our own setup is.

Okay, mine slightly blown by the hyenas.

Let's shift gears to the female reproductive system.

The basic hormonal start is similar to males, you said?

Yeah, the initial steps are parallel.

Starts with LHRH from the hypothalamus, signaling the pituitary to release LH and FSH.

Okay.

Then FSH stimulates the ovaries to get eggs ready for release, while LH stimulates the ovaries to produce estrogen.

And that kicks off the menstrual cycle.

Right.

Which typically has two main phases.

First, the follicular stage.

LHRH, LHFSH, and estrogen levels all build up, leading to ovulation, the release of the egg.

And after ovulation.

Then you get the luteal phase.

Progesterone becomes the dominant hormone produced by what's called the corpus luteum.

Progesterone's job is to prepare the uterine walls, making them ready in case a fertilized egg needs to implant.

Okay, so it's another carefully orchestrated sequence.

How does stress mess this intricate dance up?

Well, one really interesting way involves something called adrenal androgens.

Females actually produce a small amount of male -type sex hormones, mainly endrosanidione, from their adrenal glands.

Okay.

Normally, there's an enzyme, found mostly in fat cells, that converts this androgen into estrogen, keeping things balanced.

What if there isn't enough fat, like under severe stress, starvation, or maybe extreme exercise?

Exactly.

If you're starving or have very low body fat, think of malnutrition, anorexia, or even elite athletes.

You don't have enough of those fat cells doing the conversion.

So less conversion means?

Lower estrogen levels and a buildup of androgens.

And that androgen excess actually inhibits multiple steps in the female reproductive cascade.

And you see this in real life.

Oh yeah.

You see delayed puberty in young dancers or runners who train intensely.

You see irregular cycles or cycles stopping altogether that's called a nobulatory amenorrhea in women who exercise excessively.

Biologically, it kind of makes sense though, doesn't it, from an energy perspective?

Absolutely.

Sapolsky points out pregnancy costs roughly 50 ,000 calories.

Nursing takes about a thousand calories a day.

Is biologically logical for the body to say, nope, not undertaking this massive energy project without sufficient reserves.

Shutting down reproduction saves critical resources.

Are there other stress mechanisms affecting females similar to males?

Yes, several overlap.

Endorphins and enkephalins released during stress or heavy exercise inhibit LHRH release, just like we saw in males.

Prolactin and glucocorticoids make the pituitary less sensitive to LHRH.

And glucocorticoids also directly affect the ovaries making them less responsive to LH.

So the net result is less likelihood of ovulation.

Pretty much.

Lower secretion of LH, FSH and estrogen.

This can stretch out the follicular phase making cycles longer, less regular.

Or in extreme cases, it shuts down ovulation entirely and it's a novulatory amenorrhea again.

And stress can interfere even after ovulation.

Yes.

Stress can also inhibit progesterone production which is vital for preparing the uterine lining.

Plus prolactin interferes with progesterone's action.

So even if fertilization occurs, the uterine environment might not be right for implantation.

Destructions can happen in multiple points.

What's kind of concerning is that this stress induced loss of estrogen has knock on effects beyond just reproduction, right?

Definitely.

Bone health is a big one.

We mentioned those amenorrhea athletes.

They're at higher risk for decalcified bones, decreased bone mass, stress fractures, even early osteoporosis.

Estrogen is crucial for maintaining bone density.

Yeah, and the heart too.

Yeah, estrogen offers some protection against atherosclerosis, hardening of the arteries.

So stress induced drops in estrogen like those seen in socially subordinate female monkeys, for instance, can potentially increase cardiovascular disease risk.

It's all connected.

You mentioned prolactin a few times.

The book calls it extremely powerful and versatile.

It suppresses reproduction during stress, but it's also key to why breastfeeding works as contraception.

Yes.

It's not just folklore.

There's solid science behind it.

The act of nursing triggers prolactin secretion.

There's a direct reflex from the nipples up to the hypothalamus.

And enough prolactin shuts down reproduction.

If levels stay high enough, yes.

It suppresses the whole LHRH, LHFSH, estrogen progesterone axis.

But the effectiveness really depends on the pattern of nursing.

Ah, right.

This is the contrast between typical Western patterns and hunter -gatherer patterns.

Exactly.

In many Western societies, nursing might be, say, a few longer sessions spaced out through the day.

This leads to prolactin levels kind of scalloping.

They spike up, then drop back down.

But the Kalahari -Bushman study showed something totally different.

Radically different.

These women nurse very frequently, maybe for just a minute or two, but roughly every 15 minutes.

And they do this for about three years.

Wow, every 15 minutes.

Yeah.

This constant, frequent stimulation keeps prolactin levels consistently high.

No big drops.

And those sustained high levels effectively suppress estrogen and progesterone, preventing ovulation.

And the result is they naturally space their children much further apart.

Right.

Typically about four years between births.

And importantly, the book stresses this isn't because they're malnourished.

They're described as an original affluent society.

It's the nursing pattern driving the birth spacing via prolactin.

The implications for modern women are kind of staggering when you think about it.

Totally.

Think about the number of menstrual cycles.

A hunter -gatherer woman might have, what, maybe two dozen cycles in her entire life.

Compare that to maybe 500 for a typical modern Western woman.

That huge difference.

Could it explain higher rates of certain diseases?

It's a strong hypothesis.

Things like endometriosis seem much more common in populations with more lifetime menstrual cycles, fewer pregnancies, later start of menstruation.

It suggests our modern reproductive patterns might have unforeseen health consequences.

Really puts things in perspective.

Okay, let's move to another tough topic.

Miscarriage.

The book mentions this idea of psychogenic abortions.

What's the story there?

Well, the idea that stress can cause miscarriage isn't new.

It goes way back.

Hippocrates warning pregnant women about emotional upset.

Historical anecdotes like Anne Boleyn blaming a miscarriage on shock.

And it happens in animals too.

Definitely.

Simple stressors like vet exams or transport can trigger miscarriage in animals.

But there's also a darker side in some social species, competitive infanticide.

Where new males deliberately cause miscarriages.

Yeah, lions, monkeys, wild horses, baboons.

A new dominant male might kill existing infants or harass pregnant females until they miscarry.

It sounds brutal.

But from his perspective, it brings the female back into estrus sooner so he can father his own offspring.

Wow, and then there's that weird rodent thing, the Bruce Parks effect.

Oh yeah, that's fascinating.

Just the odor of a strange new male can cause a surge in prolactin in a recently mated female rodent.

That prolactin surge disrupts implantation of the fertilized eggs.

Why would that be adaptive?

Because if a new male is taken over, he's likely to kill her pups once they're born anyway.

So by terminating the pregnancy early via this odor cue, she saves energy and can become fertile again sooner, potentially to mate with the new male.

It's a harsh logic.

Okay, so what about humans?

How common are stress -induced miscarriages?

Actually, they seem to be relatively rare in humans.

And there's a timing issue too.

People often link a miscarriage to a stressful event that just happened.

But medically, most miscarriages involve the loss of a fetus that actually died days or even weeks earlier.

So the stressful trigger, if there was one, would have been much further back.

But when stress does seem to play a role, is there a known mechanism?

There's a plausible one, yeah.

It likely involves repeated strong activation of the sympathetic nervous system, that fight or flight response.

This floods the system with norepinephrine and epinephrine.

And what do those hormones do?

They can dramatically constrict blood vessels, including the ones supplying the uterus.

If blood flow to the uterus is severely reduced, the fetus can become hypoxic.

Low on oxygen and bradycardic have a dangerously slow heart rate.

Repeated episodes of this could potentially lead to asphyxiation.

So that's the potential physical link.

What about this psychogenic abortion idea?

Miscarriages seemingly caused by psychological factors.

Right, this is where things get controversial.

Some older research tried to link recurrent miscarriages with no obvious medical cause to certain personality types.

Like what?

Well, two contrasting types were often described.

One was women seen as retarded in psychological development.

Emotionally immature, very dependent, perhaps unconsciously seeing a baby as a rival for their husband's attention.

Okay, and the other type?

The opposite, almost.

Assertive and independent women who, consciously or unconsciously, just didn't wanna be pregnant.

But this research is pretty heavily criticized now, right?

Very much so, for several reasons.

First,

psychogenic is often what's called a diagnosis of exclusion.

It means doctors couldn't find a physical cause, so they labeled it psychological.

But maybe the real physical cause just wasn't understood or detectable yet.

That makes sense.

What else?

A big problem is that most of these studies were retrospective.

They looked at women after they'd already had multiple miscarriages.

So you can't tell if, say, emotional dependency caused the miscarriages, or if the trauma of having multiple miscarriages led to emotional dependency, cause and effect, or tangled.

You'd need to study women before they got pregnant to sort that out.

Exactly, you'd need prospective studies.

And the final criticism is a lack of a clear mechanism.

These studies rarely explain how a personality trait could physiologically cause a miscarriage.

While psychological stress can increase risk, the precise pathways aren't always clear in these frameworks.

Okay, so, pulling back.

Given this whole extraordinary array of mechanisms, the book describes hormones, fat levels, prolactin, blood flow.

You'd almost expect female reproduction to be incredibly fragile, shutting down at the slightest stress.

You really would.

It seems like there are so many ways for stress to derail things.

But here's the paradox Sapolsky highlights.

Collectively, these mechanisms are, in his words, not all that effective.

The system is surprisingly resilient.

How do we see that resilience?

Well, look at chronic low -grade stress.

Compare canyon farmers facing disease, parasites, seasonal food shortages with hutterites who live a simpler agricultural life without those major stressors.

Okay.

Both groups don't use contraception.

And despite the huge difference in chronic stress, their average reproductive rates are almost identical around eight or nine children per woman.

It suggests the system can buffer against a lot of chronic background stress.

Wow.

Okay, what about extreme stress?

That's maybe even more striking.

The book cites a study from the Theresienstadt concentration camp during World War II.

An absolutely horrific environment starvation, slave labor, constant terror.

Unimaginable.

In that setting, 54 % of reproductive age women stopped menstruating amenorrhea.

Which is terrible, but maybe not surprising given the conditions.

But the truly astonishing findings, Sapolsky emphasizes,

isn't the 54 % who stopped.

It's the 46 % who didn't.

Nearly half of these women still maintain some level of reproductive function.

Maybe irregular cycles, maybe a ovulatory.

But the system hadn't completely shut down, even under those extremes.

It shows this incredible, almost stubborn resistance in some individuals.

So what's the final picture here?

How do we reconcile the sensitivity and the resilience?

It seems to come down to a hierarchy.

Reproduction involves a whole cascade of events.

Some are really fundamental, basic and massive, as Sapolsky puts it, things like the egg bursting from the ovary or the mechanics of blood flow for an erection.

These core processes can be astoundingly resistant to stress.

The basic machinery keeps trying to work.

But not everything is basic machinery.

Exactly.

Then you have what he calls the pirouettes and filigrees of sexuality.

The more subtle stuff.

Libido, desire, the nuances of pleasure, arousal.

These aspects are exquisitely sensitive to stress.

They get shut down much more easily.

So the body prioritizes the basics over the subtleties.

It seems that way.

Those subtleties might not be essential for survival if you're, say, a starving refugee or a wildebeest running from a lion.

But for us, living complex modern lives, those fragile and evanescent joys, as he calls them, are incredibly important.

They're a huge part of our wellbeing and connection.

Okay, so wrapping up this deep dive into Sapolsky's chapter seven, what have we really learned?

Well, we've seen stress hits reproduction hard in both men and women.

It messes with key hormones like testosterone and estrogen, disrupts the nervous system needed for things like erections, throws cycles out of whack.

We saw how things like endorphins, prolactin, even body fat levels play surprising roles.

And we got that wild hyena example showing evolution can produce totally different roles.

Yeah.

And I think the core takeaway is this contrast.

The fundamental biology of making babies can be incredibly tough, surprisingly resilient, even under awful conditions.

Right.

But the more nuanced, pleasurable psychological aspects of sex and intimacy,

those are really vulnerable, very easily disrupted by stress.

Like, our bodies prioritize basic species propagation over the, well, the joy of it all when things get tough.

Which leaves us with a pretty important question for you, our listener, to think about.

In this world we live in, often prioritizing performance, productivity,

all that stuff that causes stress.

How do we actually balance that?

How do we protect these fragile and evanescent joys that are so important for our connection and wellbeing?

Yeah, what does it really mean to be informed about this dance between our minds, our bodies, and the stress we face every single day?

Something to ponder.

Indeed.

Thank you so much for joining us on this deep dive.

We really hope exploring this chapter has given you a richer understanding of just how connected stress and reproduction truly are.

From all of us on the Deep Dive team, thanks for listening.