Throughout my wife’s pregnancy, it seemed like everyone who already had kids was eager to tell us about the changes parenting would bring to our lives. Some were mundane but a little scary (losing the opportunity to shower every day), others profound and hopeful (a powerful new sense of purpose).

At any rate, most of them were right—just a few weeks into her life, our daughter has already changed me in many ways. Some new experiences seem par for the course—feeling less annoyed by crying kids on planes, embarrassingly tearing up to dad-themed commercials—but other changes have surprised me. I’ve grown more suspicious of strangers, for example. I’ve mentally rehearsed potential sidewalk conflicts. I’ve researched nearby boxing gyms, as though by becoming stronger or more threatening, I could somehow keep her safe.

To me, these unexpected changes are personally troubling but scientifically interesting. For the last 10 years, I’ve studied the psychology of empathy: people’s ability to understand, share, and care about one another’s emotions. Although it’s often construed as a fixed trait, empathy expands and contracts with life events. Past research has shown that people who endure hardships tend to treat others more compassionately. By contrast, years of medical training can decrease doctors’ connection to their patients’ suffering. And yet scientists know almost nothing about how having children—among the most titanic and most common life changes—affects empathy.

Based on my (admittedly limited) experience, I have two observations. First—and this one is easy—I feel empathy for my child on a scale I’ve never experienced before. Second, I can feel my empathy for others sometimes diminish in her presence. A spate of research on parenthood and family suggests that I’m in good company.

In 1956, the pediatrician and psychoanalyst Donald Winnicott described “primary maternal preoccupation,” new mothers’ single-point focus on their infant to the exclusion of almost anything else. Winnicott emphasized that such preoccupation would be a sign of acute mental illness under most circumstances, but postpartum, it equips mothers to respond to newborns’ ever-changing needs. Twenty years later, Martin Greenberg and Norman Morris balanced the parental-gender equation with a study describing new fathers’ “engrossment” with their babies. “Engrossment,” they write, is “more than involvement … engross means to make large. When the father is engrossed with his individual infant, the infant has assumed larger proportions to him.”

Parenthood enlarges parents, too. After having his daughter, my friend and academic mentor Kevin Ochsner told me he was floored by parenthood’s “heart-expanding” effects.  His description sounded like a spiritual analogue of wearing contact lenses for the first time: Details he never knew he’d missed had emerged all of a sudden, the world sharpening to a state of hyperrealism.

Psychologists argue that the need to support helpless offspring drove the development of neural, chemical, and psychological sensitivity to others’ needs. These same responses can also inspire all sorts of prosocial behaviors towards non-family, from large-scale philanthropy to everyday acts of kindness. Through the course of evolution, the story goes, children taught parents how to care.

They’ve also taught us new ways to worry. In 1999, the psychiatrist James Leckman found that new mothers study spent, on average, 14 hours per day thinking about their newborns. Much of this time was spent on positive feelings, but it also included recurring fear for their child’s safety. Like someone repeatedly checking the stove to make sure it’s off, new parents vigilantly search for any risk to their baby. In the weeks before her due date, my wife would panic whenever she noticed our daughter hadn’t kicked recently. Meanwhile, I put our bassinet through repeated midnight stress tests in a futile attempt to rid myself of the mental image of it collapsing around our daughter.

Anxiety like this can turn people inward, limiting our ability to care for others. A team of researchers at McGill University, for instance, recently found that stress inhibits empathy for others’ pain in both humans and mice. Parental nerves can also double down on another core feature of human psychology: our tendency to split the world into us and them. These social boundaries can be biological (old versus young), cultural (Yankee fans vs. Red Sox fans), or momentary (one pick-up basketball team versus another). Each type of division causes people to elevate their own side and fail to empathize with the other. And when people are stressed, past research has found, they’re more likely to feel a stronger sense of “groupiness” and to help only others who are close to them.

The moment she was born, our daughter created a new group: my children. Just as suddenly, everyone else joined another group: not my children. Family, the most powerful and smallest us to which most people belong, carpets the world in a vast, undifferentiated them. This boundary can dampen our empathy for outsiders, especially when they might imperil our own tiny tribe. In a study published last year, psychologists tested this idea by approaching women in Tel Aviv to ask their opinions about Israel’s Eritrean immigrants. In some cases, they first described these immigrants as threatening; in others, they did not. Crucially, about half the women interviewed were carrying infants at the time, and about half were alone. Women with babies in tow reported harsher views of immigrants than those without—but only in the condition where the researchers had described them as threats.

Sometimes merely thinking about family can spark exclusionary attitudes. One 2012 study asked people to write about either a recent Thanksgiving dinner with family or a recent shopping trip. The researchers then measured participants’ willingness to dehumanize outgroups by asking them to endorse statements like, “Some people deserve to be treated like animals.”  Participants who had just written about family time were more likely to agree.

I certainly felt myself become more protective during my wife’s pregnancy, but I’m pretty affable, and I can’t imagine that changing much now that I have a kid. To me, the risk is not that fatherhood will cause me to feel antipathy for outsiders, but rather that I’ll feel apathy towards non-family members—in essence, that caring for my daughter will make it harder for me to care about anyone else. Will I still be able to invest in my friends’ hopes or my graduate students’ tribulations when she needs me so much more than they do? I know what Kevin meant when he describes parenthood as heart-expanding. But by funneling our empathy into one person, it might contract us, too.

At issue here is a bigger question about the nature of empathy. Is it truly a finite resource, in which caring intensely for certain people leaves us unable to care about others? There is almost no research to answer this question. The closest psychologists have come is the study of “compassion fatigue,” a term coined by the nurse Carla Johnson in the 1990s to describe nurses so emotionally invested in their patients that their own mental health suffers. As she described it: “Human need is infinite. Caregivers tend to feel ‘I can always give a little more,’ but sometimes they just can’t help.”

Some scientists argue that tradeoffs like these are baked into the nature of empathy itself—which would mean that parenting really is an emotional seesaw, maxing out our investment in our children at the cost of our broader social connections. (If this is true, empathy might be a darker force than people often assume.) But other psychologists, myself included, follow emerging evidence to a different conclusion: Empathy is more flexible than it appears. This means that even when our care for others tends to falter, we can choose to build it back up—and that new parents might find ways to retain or expand their empathy for the world beyond their children.

By way of analogy, consider self-control. Scientists have long held that will power is like a muscle that tires with repeated use. For instance, studies have shown that people who toil on attention-demanding tasks often “run out” of control, later eating more unhealthy food or otherwise succumbing to temptation. A few years ago, my colleagues Greg Walton and Carol Dweck challenged this model by demonstrating that self-control indeed runs out, but only among people who believe it does. In their studies, people who instead believe that will power is renewable held on to their control abilities longer.

Based on my own research with Dweck, I have a hunch that empathy works the same way—people are most likely to run out of it when they believe they have only so much to give. Some psychologists have drawn distinctions between two types of empathy: vicariously sharing someone else’s pain, and compassionately wishing to improve others’ experiences. In this view, the former leads to emotional fatigue, while the latter rejuvenates. People who construe empathy as compassion, therefore, might find more space for it within themselves.   

A few weeks ago I met my daughter, the first stranger I’ve ever loved. Evidence suggests that she will enlarge my capacity for empathy, and might constrict it too.  I have no idea what will happen. What I do believe—my most important hypothesis—is that empathy is a choice, and that it will be up to me to choose how to wield it. I hope I can choose to provide my daughter with examples of warmth and openness, not aggression and parochialism. Even if having a child tempts me to close off my empathy, raising a child requires me not to.