In this episode of the Quillette Podcast, host Zoe Booth speaks with Dr Dani Sulikowski, an evolutionary behavioural scientist and senior lecturer at Charles Sturt University.

They discuss the sociocultural and evolutionary forces driving the collapse in fertility across Western societies. Dr Sulikowski examines how intrasexual competition among women, declining testosterone in men, and shifting norms around gender and motherhood may be suppressing reproduction—often unconsciously.

The conversation also explores contentious topics such as surrogacy, abortion, and assisted dying, viewed through the lens of long-term civilisational sustainability.

Transcript

Zoe Booth: I’ve been very interested in this topic of fertility decline. It was something I was never that interested in until I turned, I don’t know, 28, 29, and started thinking about having kids myself, and now I’m obsessed with the topic. Australia has a declining fertility rate like most OECD nations. You have some really fascinating theories on why that’s the case. Could you tell our audience a little bit about your theory?

Dani Sulikowski: Okay, so we can start small and then continue to add layers and get more big-picture and more complex. But the very basics of human behaviour—or indeed any animal behaviour—is this idea of competitive reproduction.

The currency of evolution is reproductive success. If you have more offspring in the next generation, your genes become overrepresented in that generation. If that continues, generation after generation, then your lineages effectively dominate and come to be what’s there. Therefore, whatever behaviours and any other traits those genes cause due to behaving well—that becomes how the population behaves. Right? Basic principles of selection.

What that means is that all individuals are under selection pressure to win that competitive race. That means not just maximising your own reproductive success, but actually minimising the reproductive success of rivals around you. That’s what we call intrasexual competition.

ZB: It’s fascinating, and I assume men and women have different ways of reducing that reproductive capability in rivals?

DS: Yeah, that’s right. The fundamental biological difference between men and women is that men have the small gametes—sperm—which they give to the women. Women have the large gametes, which means they receive the opposite sex’s DNA, and then they’re the ones actually responsible for making the offspring.

Most people are probably familiar with the idea that a population—or a society—can and frequently does send large numbers of men off to fight and die in wars. And the reproductive capacity of the population doesn’t necessarily change as a result, because women are the rate limiters of population. Right? Women, by virtue of how reproduction works, can have a finite number of children. Men can potentially father an infinite number.

So a population can afford to sacrifice a lot of men in something like a war. And the small number of men left are sufficient to support the women remaining to effectively replace the lost men in one generation. You can’t do the same thing with women.

ZB: I’ve heard it explained as sperm is cheap and eggs are expensive—perhaps the most expensive per pound. I think our writer Rob Brooks said that it’s not diamonds or oil, it’s eggs—human eggs.

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DS: That’s right. They’re very valuable. They’re kept inside. Men’s sperm can be spread around anywhere, but because women’s eggs have to be kept inside and take an entire woman to percolate over time, you can only do one at a time. Maybe two if you’re lucky, but essentially one-point-something on average—not many.

So now, looking at it from the position of intrasexual competition, if a woman wants to increase her net reproductive success, she needs to reproduce at a rate greater than the background population rate—so she can have more babies. That’s one way. Another way is to try to reduce the net reproductive rate by influencing rivals to have fewer children.

If you have two children in a population where the background population rate is 1.8, then you’re winning that intrasexual competition race. You’ll become overrepresented in the next generation. If you have two children in a population where the background rate is 2.2, you’re losing. So manipulating the background rate by even a small amount can be the difference between your genes gaining or losing ground in the next generation.

Now, this is something women can do. Limiting other women’s reproductive capacity can lower the overall background rate. Men can’t really affect that by limiting other men’s reproductive capacity—for the same reason we can send huge numbers of men off to war and recover in a generation. Even if a man convinced other men to withdraw from the gene pool, the small number left could still sustain reproduction.

So this technique—manipulative reproductive suppression—really only benefits women.

When men engage in intrasexual competition, it’s a running race: just have as many babies as you can, eyes on the prize, ignore what everyone else is doing. For women, it’s much more about promoting your own reproductive success and investing energy in pulling your competitors back behind you.

That’s the reason for the sex difference. This is a female phenomenon—much less so a male one.

ZB: It’s hilarious to even think about men trying to manipulate other men into not having kids—like boycotting sex. Like men would ever boycott sex. It’s a ridiculous idea. Or they’d say, “Yeah, sure mate, I’m going to boycott,” and then definitely not boycott.

Whereas with women—I talked to Holly Lawford-Smith, who’s a radical feminist academic—and one of the best soundbites from that podcast was her radical idea (which other feminists have said as well): that women should be boycotting sex. It sounds crazy to hear, but you hear variations of it. You hear women say, “I’m sick of men. I’m sick of dating. I’m not doing it anymore. I’m not trying to find a partner. I’m going to be single forever and live with my cat—and I’m fine with that. And if you have an issue with that, you are a bigot,” essentially.

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DS: Oh yeah. And it’s not just in everyday conversation either. It’s part of social discourse now—this narrative that having children oppresses you. It limits your career, your freedom, and has all these negative impacts.

And that’s not just an Australian phenomenon. It’s not even Western-specific. South Korea, if I’m not mistaken, probably has the lowest birth rate at the moment. I think they’re “winning” or “losing” depending on how you look at it.

They’ve had for quite a long time a cultural slogan—it’s referred to as the “Four Bs.” I believe the four words in Korean mean: don’t date, don’t marry, don’t have children. It’s a really strong cultural movement.

And we see this in politics too. You may remember when Trump won the election, a whole bunch of women came out to protest by shaving their heads and declaring they were not going to get married or have children. There were even women having their tubes tied in response—as some kind of feminist, left-wing, or “woke” attack on reproduction.

It perhaps started more gently, but it’s ramping up. My argument around feminism is that I used to say it began as a movement interested in women’s place in society but was co-opted by what’s effectively become reproductive suppression.

Now, I think feminism was always an attack on reproductive output. That’s all it’s ever been. And I think you can explain it from beginning to end with that one principle.

ZB: Such a fascinating topic. I want to go back slightly to this idea that I always knew, but it’s really dawning on me now—just how important and integral sex is. The act of it, but also reproduction, to the human species.

And that, as a woman, that’s why the rape of a woman is such a—such a—is it “derogation”? No, that’s not the right term.

DS: Violation, maybe.

ZB: Violation, yeah. And obviously it is for men as well, but there’s something about it for a woman—because it’s your innate power. As you were saying, women are the reproductive limiters. We have the choice. And when that choice is taken away from you, it’s such a gross violation.

And I guess by women using their sex to negotiate or to protest—it’s such a deep thing. It’s like the last sort of power you have as a woman, to say yes or no to sex, in a way.

DS: Yeah, it is. And I think you’re absolutely right about rape having a very unique position psychologically—because it is, perhaps second only to murder, a complete violation of what almost all aspects of our psychology have been selected for over many years to maximise and finesse: that mate choice and that reproductive success.