Fertility is a Network Effect
How social connections shape birth rates
Second lady Usha Vance announced that she’s pregnant with the Vances’ fourth child this week, joining other prominent Republican women like Karoline Leavitt and Katie Miller who are expecting. In response to a joke by Laura Bassett that Republicans are “spawning,” Tim Carney noted – as he previously did in his book Family Unfriendly – that pregnancy is “contagious.”
I think that Carney is right. One part of a broader project I’ve been working on is trying to see if there really is a link between the fertility of one’s peers and their own fertility. While the empirical analysis is still in progress, this way of thinking about fertility is useful for understanding why fertility rates have remained so low.
Much of the discussion about declining fertility has focused on individual-level explanations: cost of childcare, student debt, housing prices, personal preferences, and marriage timing. Of course all of these matter, but they share a common assumption that fertility decisions are made in isolation. My research (and Carney’s point) starts from a different premise: people don’t make fertility decisions alone. Decisions about if/when to have kids and how many kids to have are made while embedded in social networks that shape what feels normal, desirable, feasible, and rewarding.
In other words, fertility could be conceived (pun intended) of as a network effect.
In economics, network effects describe situations where the value of someone doing something depends on how many other people around you are doing it too. Apps like Instagram, Venmo, Hinge, and Lyft are only worth using because a significant number of people are also using them enough to make it useful. Same went for landlines and the internet. The same economic theory can also be useful to help explain why fertility has been falling precipitously.
What Does it Mean for Fertility to be a Network Effect?
There is a great paper written by Matthew Jackson in the Journal of Economic Perspectives that gives the case for why economists should model network effects in their effort to understand human behavior. In the paper, Jackson gives a three-pronged typology of network influence that may change our decision making:
Shared knowledge
Cultural norms and expectations
Mutual Support
All of these are – of course – relevant for decisions regarding fertility. We learn from our peers, conform to the norms of those around us, and rely on others. If you rarely see friends or family having children, or if no one in your orbit has young children, that shapes both your expectations and your practical sense of feasibility.
My argument is that in low-fertility contexts, these social dynamics create a negative network effect – each marginal decision not to have children slightly reduces the incentive or the viability for others to do so.
Shared Knowledge
There are many unknowns surrounding having children. It’s impossible to approach parenting with perfect information, but we can glean information from watching others go through different parenting phases.
Watching how peers navigate pregnancy, childcare, and work-life balance provide information about what it will be like to parent. Friends and family show us how people “like us” manage the transition to parenthood, reducing uncertainty about timing, tradeoffs, and feasibility.
This learning happens naturally when you have a lot of parents in your social circle and that learning can help make parenting seem less scary. But when exposure to parenting and children declines, uncertainty rises and parenthood seems harder to imagine concretely. Even people who want children may delay fertility because they don’t have enough information about their specific circumstances to feel confident moving forward.
The social environments we live in fill in gaps where formal information is incomplete. Decisions about having children are complex and learning by watching is how people manage that complexity.
Cultural Norms and Expectations
While we learn from our peers’ experiences, we also benchmark ourselves against their experiences and timelines. The behaviors of those around us set both descriptive norms – what’s typical – and injunctive norms – what’s approved.
Other work on the network effects of fertility has shown that the descriptive norms around when to have children are enforced by approval or disapproval. The norm around when to have children is set by a feedback loop of your peers. Choosing to get married and have children before graduating high school will likely lead to social disapproval, while getting married and having children in your late 20s and early 30s is a socially validated decision. Fear of violating these norms – whether or not they reflect personal preferences – can be pervasive. Importantly, no one needs to explicitly discourage childbearing for norms to shift – the absence of children does the work of showing what is “normal.”
As childlessness becomes more common in a network, it can feel easier to postpone parenthood without ever making the explicit decision to do so. Setting into the norm that childbearing doesn’t happen until after 30 can accidentally lead to forgone fertility.
Once these norms have evolved, they’re hard to reverse. Defecting from the norm risks losing your social circle. If you choose to have children prior to your peers, you may be socially isolated as your needs and constraints change. Alternatively, if all of your friends are parents and you choose to remain childless, you may end up on the outside of playgroups and babysitting sharing. The culture surrounding childbearing in your friend group can greatly affect the decisions you make regarding having children, even if it’s subconscious.
Mutual Support
Many of the benefits of having children only exist when others around you are also parents. Informal childcare arrangements, hand-me-downs, advice networks, and playgroups all depend on having a critical mass of families. These relational dynamics can reduce both the monetary and non-monetary costs of having children.
Conversely, when few network members have children, these informal systems disappear and parenting can feel more isolating and costly. At the macro level, this can also extend to institutions. As more members of a broader “network” or community have children, schools, employers, and local governments become more responsive to community needs. We can already see the alternative being true now, with the majority of government social support going to the elderly instead of children and with the closing of schools as a result of a smaller number of pupils.
Both the informal and formal create a pervasive feedback loop. As support erodes, it becomes harder to have children. As it becomes harder to have children, fewer people choose to be parents. Fertility can then become self-limiting over time – not because people don’t want children, but because their social environment no longer supports the choice.
The Social Nature of Having Children
These three mechanisms enforce each other. When fewer people have children, there are fewer people to learn from and benchmark against. This in turn shifts norms about having children, which weaken social support systems. Each mechanism amplifies the others, creating cascading effects.
This can help explain why low fertility has been so pervasive. Once a community falls below a certain level of exposure to children and parents, it can be trapped in a low-fertility equilibrium. Even substantial policy changes may struggle to reverse the trend because there has been so much change to the broader social ecosystem.
Understanding how fertility can be shaped by our networks means that family policy has a major hurdle. To be effective, family policy needs to alter incentives that vary greatly across communities. Many of these differences are hard to identify without understanding the social networks people are embedded in. This is why I’m such a big proponent of housing reform, flexible work, and increasing the supply of child care over baby bonuses and baby bonds. Policies about housing, labor, and child care focus on the environment people raise children in which can make defecting against or conforming to norms easier, depending on the network. Survey data also shows that these policies are what families demand over financial incentives to have children.
People still make deeply personal decisions based on values, relationships, and life goals – fertility rates among the religious are generally more durable across time and location. But all of these decisions are made within social contexts that alter what feels possible and normal.
If we want to better understand why fertility rates are falling, we need to color in more of the picture. The individual matters, of course, but so do the networks that surround them.
Time Users
What I’m Reading: The Art of Vanishing by Morgan Pager
Something I Found Interesting: This paper on how much female economics students benefit from having female faculty around. When female professors go on sabbatical, it decreases the odds that female students publish and get academic positions while male students see better outcomes
What I’m Listening To: I couldn’t stop listening to the audiobook The Mother Next Door by Andrea Dunlop and Mike Weber earlier this week. Since finishing the book, I’ve been listening to Dunlop’s podcast Nobody Should Believe Me. Both the book and the podcast are fascinating accounts of Munchausen By Proxy
What I’m Making: After months of my husband asking me to, I was finally brave enough to make focaccia for the first time! I used the recipe from the Bread Bible