Not long ago, my toddler, Atlas, bounded into the kitchen exclaiming, “Mommy, come see the river!”

I cringed, recognizing that a river might have several meanings to a 3-year-old who loves playing with faucets and still hasn’t perfected potty training. When he pointed toward the hallway where we have a map, a wave of relief washed over me. Maybe I ought to trust this kid more.

Then I saw it — two long black wavy lines of indelible marker coursing down the wall.

“I made a river,” he announced sweetly, “just for you!” as I realized I now had a new painting project.

Parenthood isn’t easy, but lately it seems to be getting an unnecessarily bad reputation. One widely cited study of 22 countries recently reported that parents tended to be unhappier than non-parents. And they attributed this “parenthood gap in happiness” to the financial and other stress of raising children “in countries that do not provide public assistance,” such as subsidized day care and paid parental leave.

Sheril Kirshenbaum holds her son. “Children can be exhausting, isolating and expensive,” says the author. So “why do we keep having them?” (Courtesy of Kirshenbaum Family)

The Department of Agriculture estimates that Americans spend an average of $245,000 per child between birth and age 18. And then there’s the stress of small stuff like sharing my house with a three-foot-tall graffiti artist.

Children can be exhausting, isolating and expensive. So if they truly make us unhappy, why do we keep having them?

Our ancestors required big families for hunting and farming, but that’s not necessary in the 21st century. As a mother, I know I wouldn’t trade the experience for the world, but my years as a scientist made me curious about what research can tell us. I dug into the findings, and it turns out there’s a lot of evidence for how children affect the physical and emotional life of their parents and a myriad ways in which they can boost both our health and happiness.

Parenthood certainly doesn’t start as a cakewalk: Friends and I jokingly refer to the first three months as “100 days of darkness” while on call 24/7 in an endless cycle of feed, wipe, bathe, repeat. Yet we persevere, and that’s in part because of the way that nature tricks parents into adoring their tiny new minion.

Early on, we enjoy a kind of natural high by staying close to and caring for a baby. A newborn’s scent triggers an increase in a mother’s brain of dopamine, a chemical associated with anticipation and reward. This neurotransmitter brings about feelings of intense pleasure and is associated with addiction. Dopamine essentially makes us crave being with the baby. Long after infancy, moms can experience the same dopamine-reward response simply by seeing their child smile. In a sense, when our kids are happy, we feel it.

Dopamine isn’t the only chemical working on parents. Yale University scientists have found that both mothers and fathers experience a rise in levels of oxytocin when a baby enters the family. Often called “the love hormone,” it promotes attachment, a sense of euphoria and intense love while decreasing stress. It also helps to buffer against challenges like sleep deprivation.

Richard Weissbourd, a Harvard psychologist with the graduate school of education, and the Making Caring Common Project have come up with recommendations about how to raise children to become caring, respectful and responsible adults. (The Washington Post)

The first months can be tough, with aches and pains, bleary eyes and the baby blues — or worse — for some women.

But hormones and neurotransmitters usually fool us into believing that our baby is the most wonderful creature in the world. Yes, we may be temporarily delusional, but this naturally occurring chemical cocktail helps us make it through the exhaustion and even forget enough of that period so that we’re often willing to do it all over again. Fortunately, there are major perks for going through the struggle.

A study of nearly 140,000 postmenopausal women found that those who had breast-fed their baby for at least a year had a lowered risk for several serious health conditions, including Type 2 diabetes. They also had a lower incidence of high blood pressure, heart disease and breast and ovarian cancer . We often hear that “breast is best” for baby, but while it can be a pain for moms — quite literally — it appears to lead to long-term health benefits.

In the shorter term, of course, kids can — and frequently do — make us sick. Comedian Louis C.K. once aptly noted, “Kids are like buckets of disease that live in your house,” which seems to be my day-to-day reality.

When my son comes down with a bug, I’m not just exposed to germs, I’m usually elbow-deep in them. On multiple occasions, he has managed to cough directly into my mouth. My husband recently shared our son’s bout of hand, foot and mouth disease — timed perfectly for a job interview.

However, the data suggest that parenthood actually offers some protection from illness. Scientists at Carnegie Mellon found that mothers and fathers exposed to a cold virus are less likely to get sick compared with non-parents.

But while health and happiness are strongly correlated in many studies, that doesn’t necessarily translate for parents. When Princeton and Stony Brook scientists surveyed 1.8 million Americans, they found that while “parents and non-parents have similar levels of life satisfactions,” parents often had more emotionally intense lives: They expressed higher highs and more joy than non-parents, although they also reported feeling more worry, stress and anger.

In other words, parenthood fundamentally changes us, often in surprising ways. Being a mother or a father tends to require that we become less self-involved and more generous with others — that is, with our kids. It provides a strong sense of purpose while fostering lasting social connections — two of the most important qualities, according to a growing body of research, for a happy life.

Some of the changes may even be physical. Psychologists Kelly Lambert and Craig Kinsley concluded that raising children leads to changes in the brain that make mothers more empathetic and nurturing. Evolutionarily speaking, these qualities can help give kids the best possibility of survival.

Parenthood forces our brains to shift from a world mainly consisting of “self” to one consisting of both “self and other.” The rules for how we act change when a baby enters the picture. New situations and experience rewire brain circuitry, neuroscientists find, which helps us adjust to life as a mother or a father.

When psychologists at Michigan State University analyzed data on the origins of parenting behavior from 20,000 families around the world, they concluded that genes affect how we express warmth, control and negativity toward kids.

From an evolutionary perspective, parents who are best able to understand and meet the needs of their children are generally most likely to pass on their genes. In this way, evolutionary experts say, the most nurturing qualities may have been promoted to persist in humans over subsequent generations.

Of course, parenthood isn’t for everyone, and it certainly is not required to live a fulfilling and purposeful life. Without supportive social policies to ease work-life balance, it can be a financial and emotional drain.

Still, becoming a mom or a dad forges one of the most significant bonds that we can experience, and studies have found that long-term happiness often stems from these kinds of important relationships established throughout our lives.

It’s true that those who choose to have kids are saddled with relentless responsibility and little free time. And parenthood also comes with physical transformations such as stretch marks, weight gain and the classic “dad bod” that might not always lift our spirits.

But a review of the research reveals that the return on investing years and energy into having children can’t be tallied in terms of a net gain or loss of happiness. It’s just not as simple as a one-size-fits-all equation. What data do reveal is that under the right circumstances, kids have the capacity to bring out our best selves, emotionally, chemically and biologically — even when it comes with scribbled hallways and sleepless nights. And I find that reassuring, especially as I embark on the adventure for a second time.