“Is it okay to still have children?” Congresswoman Alexandria Ocasio-Cortez asked her social media followers in 2019. She was addressing a growing reluctance among young people to consider parenting; both because of concerns about overpopulation and because of concerns about what kind of world new children would be coming into. This openness about rethinking parenthood is recent, but it’s happening in the context of a much longer global decline in births. That decline, steadily underway for the past 50 years, may be accelerating. Between 2019 and 2020, births declined 1.12 percent; the following year that number rose to 1.13 percent; the latest decline reported between 2021 and 2022 is 1.15 percent.
Why is this happening? The word “multifactorial” doesn’t begin to cover it. You hear a lot about women and education, and access to contraception. People also float the possibility of environmental toxins. You might not think of your social network as an environmental toxin, but that’s the idea Alexander Suvorov put forward last year in a paper published in the journal Endocrinology. Suvorov, a biologist at the University of Massachussetts Amherst, thinks that changes in our social environment are somehow contributing to the drop in reproduction. I was startled by this idea so I asked him to take me through it. Our interview has been edited and condensed for clarity.
Sally Adee
This is a really hard question to untangle.
Alexander Suvorov
As always in science, when you try to address a complicated question, the approach is to split it into much smaller questions.
By answering smaller questions, you can gradually build a mosaic, to arrive at a big picture. One example: in mice and small rodents, it is well-documented in laboratory experiments, and also in wildlife, that population density, or just social interactions, generate stress. And you can measure this stress by corticosteroid hormones in blood. So what about humans? For example, if you meet with many people over the day, will the level of corticosteroids be higher in your blood? Nobody knows. It would be a simple test, but no one has tried to measure this.
Or for example, let’s say you spend all your day sitting in front of the computer, interacting with thousands of people via Facebook. Will your body generate an increased stress response? Again, that is a very simple question that can be answered by a very simple questionnaire asking people how much time they spend on Facebook and measuring the corticosteroid levels. But nobody ever did that.
SA
How come? I mean, that seems like such a basic idea. Especially in light of all the conversations around the online safety act. People are constantly talking about the harmful effects of social media – why hasn’t anybody tried to quantify it in this way?
AS
It’s very difficult to develop a whole new area of research that asks questions nobody has asked before. One reason I published the paper was to trigger this line of research: to demonstrate that the amount and quality of social interaction can affect behaviour significantly.
SA
Please can you explain what you mean by amount and quality of social interaction?
AS
Our species evolved for millions of years in the African Savannah. The standard size of human groups was around 150. The idea is that this is the upper limit of the number of people with whom we can maintain meaningful social connections. It doesn’t mean that those people are your friends. Some of them may be quite opposite – your enemies – but at least you understand that they are enemies, meaning that those connections are of high quality. You can predict the behaviour of those people. You can model them in your head. You understand the resulting social environment very well, and that makes your brain feel happier. But as the number in your group starts to grow into the thousands, your brain starts to feel like it is completely out of control, because you cannot keep that amount of high quality models of people in your memory. The physical size of the brain structures responsible for social interaction and modeling even indicates that the number is optimally 150.
SA
What happens when your number – that amount – rises too far above that?
AS
The bigger social networks enabled by the internet, I think that they can be a significant source of stress. That is what I think. Unfortunately as yet it is just my opinion. I have to disclose that.
So imagine a small village from 100 years ago, and let’s say in that village, there are 10 young people, late teens, early 20s, trying to find their place in this small rural community. They’re fighting for their place. One of them is the strongest. The whole village appreciates how strong they are. Another is, I don’t know, the best dancer. The third is so handsome that every girl likes him. Then there is the great storyteller. The one who can fix any car. Right now, in this small village, everyone can feel themselves absolutely accomplished.
Each has found their own place in the hierarchy, the smaller pyramid on which that person is the best, bar none. In this situation, everyone is fine. People are happy, they have a place, they know that they’re best in something.
Now give all these people access to the internet. The one who is strongest goes on the internet – and sees the Strong Man competition where entrants are a thousand times stronger. He now feels he is a loser. The same thing happens to the best dancer and the one who can fix a car. This access to internet and to all of social media generates a feeling of not being accomplished for everybody, because only a few people in the world really are the best. Everybody else is not.
Sally
Okay but…. the world has not always offered only a binary of either life in a small village of 150 people or a firehose of all 7.5 billion people on Earth. There were intermediary experiences, like living in a city with loads of great dancers or, you know, cable news telling you about the Nobel prize winners. Is there a linear relationship between stress and the amount of exposure to people above you in the hierarchy?
Suvorov
There’s no direct evidence, because no one has tried to look at it. But there is indirect evidence. Much of it comes from recent studies of happiness. Many such recent studies demonstrate that there is a gradient of happiness – with the happiest people living in the smallest settlements, and the most unhappy people living in the centers of big cities. Several of these – from the United States, from China, from other countries – all arrive at similar conclusions. So the smaller your social environment, the happier you feel.
SA
So that’s the effect of a large amount of social interaction. But you are also worried about the quality. In the commentary that accompanied your paper in Endocrinology, there was a discussion of the different kinds of interactions: distinguishing between “opportunity” interactions versus “challenging” interactions. What do you mean here?
AS
There’s one aspect of all of this that I think many people do not recognize: The way aggression has evolved in society.
In 1963, the Nobel prize-winning scientist Konrad Lorenz wrote a book called On Aggression. I believe that that book was the most significant discovery in the area of human behavior – ever. No one has improved on his work since then. He was recognized as a fantastic scientist by Nobel committee, but the book fell out of favour because he was an Austrian scientist who supported Germany during World War II. That was unforgivable, but it is unfortunate that his work does not survive, because it contains important insights.
It’s complicated. He was accused of making some statements that he never did. One enduring piece of misinformation about him is that he provided the justification for the war, because of his discovery that aggression is a fundamental human instinct. But he never wrote that this aggression made war inevitable. Quite the opposite, in fact: he explained that the instinct of aggression – in humans and in many other species – is undergoing steady evolution. And that it is producing behaviour intended to resolve a goal without doing physical harm.
SA
And what is the goal?
AS
To establish dominance. The purpose of aggression is to build social hierarchies where the strongest will be dominant. He or she will fight until everybody else is defeated, and only they remain, and that defines them as the dominant one. But in developed society, to establish your dominance, physical aggression is no longer as necessary or desirable. Instead, you get a great education, and collect degrees and diplomas. These are today’s ritualised behavioural signals which – without any fighting – will put you at the top of the status pyramid. And that was actually what Lorenz’s book was about. He was explaining how this aggression instinct has pushed humanity to build these complicated social hierarchies, and how human interactions have therefore evolved to become less physically harmful while still conveying the message of your level in comparison with others.
SA
So status-seeking behavior is evolving away from the ape-like behaviour of, just, like smashing each other on the head like in 2001: A Space Odyssey?
AS
People can of course still continue to fight physically, though it is an increasingly uncommon way to establish social dominance. But just because there is less physical fighting doesn’t mean there is no aggression. Aggression is everywhere. When you meet with friends, colleagues, whoever, talking with them or working with them, you never think about what it is you are really doing: constantly comparing yourself with others to evaluate if you are higher or lower. Every time you communicate with other people, you are building this social hierarchy. We never think about it consciously, but it is happening every second.
It has come so far from the original violent dominance contests, that we no longer recognize it as such. But in reality, every time we communicate, it is at least partly driven by aggression.
And our brain subconsciously knows that, meaning that every time you meet with people – even friends – there are small stress signals generated because your brain is always on alert: Knowing that what you say or what others say may somehow affect your level, and you might go down. But in my opinion, Konrad Lorenz created the theoretical framework that allows us to understand that even ostensibly harmless interactions can produce some physiological stress response in our brain. Consciously we do not recognise that we are engaging in aggression, but our subconscious knows it.
SA
I guess that helps me understand why people do certain things. Even before social media was ubiquitous, we were using the internet to rank ourselves. There was this website called hot or not dot com where you would upload photos of yourself in order to then be rated by random strangers.
AS
People willingly put themselves on display to build their rank, yes, to fight for a high place in the hierarchy. On top of that, we have now developed this technology – electronic means of communication- that can change how our brain perceives our environment completely.
SA
So it’s really stressful to compete for status. In your paper you speculate that this has physiological consequences?
It wouldn’t be so controversial to say mental stress from some particular source could impact physiology – that the stress of “lower quality” social interactions could lead to biological consequences. After all, “the brain is intimately connected to the body and the body to the brain,” David Spiegel at Stanford University School of Medicine told the New York Times last year. “The body tends to react to mental stress as if it was a physical stress.”
AS
Pronounced trends have been registered by scientists showing a decline in reproductive physiology – both in men and women, but it is better characterized in men. For example, meta-analyses have now demonstrated a 50 percent reduction in sperm count, everywhere in the world.
My current research is mostly in the area of environmental toxicology. One popular area of research in this field is endocrine-disruptive chemicals. The default assumption is that we should attribute this drop to exposure to those chemicals. But nobody has tried to critically analyze whether this is true or not. And the reason for that is because we do not have alternative explanations. And so, the result is that every time you see some global decline in some parameter of health, people automatically attribute that to chemicals because what else could it be?
It’s not a bad hypothesis. It’s not that it doesn’t have support, it’s likely true. But nobody ever looks at other possible explanations.
SA
And your hypothesis is that in addition to all the other factors, there is also some kind of awareness of overcrowding, some awareness of population increase, that has increased in the past 50 years? And you think social media is exacerbating this perception?
AS
I feel that social media is one of the most significant factors that is affecting human behaviour today. These events, the pandemic, the economy, Ukraine. If they had happened in the 19th century – and so many did! – people would continue focusing on our duties, on our friends, families, our job, and et cetera. But today, the whole world is glued to social media, monitoring what is happening – including myself! And we cannot stop doing that. Those events are substituting for our personal lives. And there’s always something bad happening, so we never stop.
SA
But linking stress and social media use and reproductive consequences would be a difficult experiment.
AS
Yes but we can do it. We don’t have a lot of data from humans. So now we need two types of studies with humans. First, we need to see if reproductive outcomes are negatively associated with stress hormone levels – in the blood, or maybe in saliva, there are several different methods to measure them.
Second, we need to find associations between social interactions – specifically, the quality of social interactions – with stress levels. Again, measuring these via stress hormones in some biological media, saliva, blood, whatever. We still are missing a lot of data. For example, I was trying to find some historical trends for testosterone levels. We don’t know what teststerone levels were in men living 50 or 100 years ago – are they going up or down? What about estrogen? If we find that the human hormonal background is changing, it could mean that modern human beings, from an endocrine standpoint, are completely different creatures than the humans who lived a hundred years ago.
SA
What gave you the idea that this had any connection with reproduction?
AS
Anecdotally, I started to see a pattern in the families around me. The kids, at the age of around 30, have no intention to have kids ever. I’m a biologist. For me, that looks like complete nonsense. Natural selection is based on selective reproduction. Meaning that all those people who want to go child-free, they are mostly eliminating themselves from existence – because their genes will not be transferred to the next generation. Not at the personal level, but at the level of lineage, that is suicidal. Your genes will never go to the next generation. That’s it. Forever.
For millions of years, natural selection led to successful reproduction, but what is happening suddenly? And if you try to find an answer in the scientific literature, almost everything is sociology research where people say, oh, as women get more education, they deviate from this program. Or if people get wealthy. Or if they have good access to contraception. And et cetera, but that is all sociology. What about evolutionary programming, the instinct in our brain? Can you imagine a cat who suddenly says, ‘oh, I don’t want to have kittens anymore’. Or a dog who says ‘I want to live for myself’.
SA
Aren’t you conflating the instinct to reproduce with the instinct that … leads to reproduction? If you can freely engage in the latter without having to deal with the former – I mean, it makes sense to me that you might then have fewer children, or maybe none.
AS
Of course there is a drive for sex, but that’s not the only thing responsible for the production of new humans. People have maternal and paternal instincts. We like babies. And lots of people want to have a baby regardless of having sex. I don’t believe the neurophysiology of this programming is well understood, but I think that there are multiple layers in it. For example, for many people, having kids means you can propagate yourself into the future – it’s a key to immortality. I don’t think contraception alone can switch off that desire to proliferate.
SA
Right now, I don’t really blame people for wanting to maybe not bring a vulnerable new human into a world unusually prolific with war, famine, pestilence, and death. Wouldn’t that be enough to temporarily override – for some people – any biological drive to reproduce?
AS
Let me ask you the following question: In your opinion, when were the chances of survival, and of being wealthy, higher for somebody living in the United States or in Great Britain or in any other developed country today: the 15th century, or today? Of course the answer is today. Why? Because we have much better medicine. We do not suffer from starvation. We live very high-quality lives.
When people in the middle ages had wars, smallpox, syphilis, tuberculosis – or even just didn’t have enough food – they did not simply stop reproducing.
And furthermore, Covid-19 and Ukraine have only happened over the past three years. The trend for decreasing reproduction is much, much longer. Two years ago, there was a very good quality demographic paper published in The Lancet, which predicted that by 2064, the population of the humankind will reach its absolute maximum, meaning that after that population will go down.
SA
Peak human.
AS
Yes. So again: why? Today we have better than ever medical systems; we are wealthier than ever. In most parts of the world, we have resolved the problem of availability of food, and having a roof over your head. Against this backdrop, we cease reproducing? This isn’t just psychology. If we are now capable of suppressing the most basic instinct that has driven life on earth for millions of years, that means something very significant is happening at the level of biology.
That’s the question I’m asking here, is what is happening with the biology of these people? What is happening to this program that has worked for millions of years? The fact that we exist today is due to the fact that every previous generation of humans, of homo sapiens, homo erectus, homo everyone – all our ancestors, back to the first unicellular prokaryote, they all reproduced. And that continuous chain of reproduction finally came to us. And now, what is happening? Why have we stopped?
From animal models, we already have enough data that shows that increased concentration of corticosteroids – stress – suppresses reproduction in mice.
SA
Can you tell me about this?
AS
It was one of the inspirations for my work.
In the 1940s, the ethologist John Calhoun gave a group of mice everything they could want – ample water, food, no predators, and mating opportunities. The only catch was space: the rapidly proliferating mouse families had a limited enclosure into which to grow, and no constraints on that growth. The first few generations, when the population was small, were happy. When the colony hit a certain population threshold, however, everything went to hell. Cannibalism ensued, and mice killed their own babies and each others’, among a wider catalogue of horrors – but the most unsettling consequence was the increasing number of mice that withdrew from social interaction completely. Despite ample resources, some switch in their brains had been tripped (Calhoun thought it was the overcrowding), and otherwise reproductively ideal specimens – well-fed, eyes shiny, coats gleaming, the picture of health – stopped interacting with other mice. They didn’t mate, they didn’t fight, they didn’t socialise. They lay in their corners, alone, grooming themselves, until they died. Calhoun called these “the beautiful ones.” Eventually the entire colony died out.
SA
I find it really interesting how much traction this study has gotten in popular culture. More than half a century on, it still pops up in everything from sci fi books to economics papers. Awareness of his work has been unusually enduring. Why do you think it continues to have so much traction and what in your opinion was its real significance?
AS
It is a very important study. It was the first time anyone had demonstrated that population density is an important factor that determines behaviour. Not our behaviour, granted – that of mice and rats. But these are the standard models used in medical and biological research, so it raised a valid question whether it was applicable to us.
SA
Some people might argue that humans are not mice. Do you think that something like this can be legitimately extrapolated to human psychology from mouse psychology?
AS
I do. Every model in science is limited. There are things which can be modeled in mice and rats very well – for some research questions, they are perfect models. For others, they are very bad models. You just need to understand their limitations.
SA
Did the reception of the paper go as you anticipated?
AS
No. There was much more immediate interest than I anticipated. Usually you receive initially harsh review feedback. In our case it was surprisingly positive. One reviewer wrote “that is very interesting reading”. I have never, ever seen this comment before. Then the journal of the Endocrine Society decided to issue a press release about the paper; on top of that, there was an editorial commentary. So all of that was absolutely unexpected. But it was strange. Usually if a paper receives this much attention, it is cited by others. We have tools to monitor citations, and I have found that no other published studies have yet cited our paper.
SA
What else might you expect to see in the next five years, if your hypothesis is true? More missed targets for births?
AS
Existing trends will continue to go up the way they have been for a long time. More childfree families, new and different forms of social withdrawal. And people having less sex.