Nature vs. Nurture

Scientists have long debated whether heredity or environment has the biggest impact on your baby. We've found some surprising answers.
Stephanie Rausser/Trunk Archive

How much of your infant's behavior is biological and how much can you actually modify? The answer, in both instances, is quite a lot. "Nature and nurture work together to produce a personality the way humidity and cold come together to generate snow," says Jerome Kagan, Ph.D., author of The Temperamental Thread: How Genes, Culture, Time, and Luck Make Us Who We Are. For frazzled new parents, it's easy to interpret this as good news: On the one hand, you don't have to hold yourself responsible if your child is a chronic crier or is painfully shy; and on the other, there are almost always strategies that you can employ to improve her disposition. Find out what the experts say you can do to raise a calmer, happier baby.


How much is nature?

Your infant's wails are designed to be as difficult to ignore as a screeching smoke alarm. That way, he gets your attention and you get a placid, secure child when you respond appropriately. Some babies, though, are more difficult to soothe than others, and genetic makeup is a significant factor. "Researchers believe about 60 percent of temperament is hereditary," says Parents advisor Harvey Karp, M.D., author of the book and DVD The Happiest Baby on the Block. If, like 15 to 20 percent of all babies, your child is extremely sensitive -- so alert to everything around him that he quickly becomes overstimulated -- there's a higher probability that he'll have lengthy bouts of bawling. Many physicians have stopped using the term "colic" (which was once defined as crying for more than three hours a day for at least three days a week) to describe this condition, "but most parents have a good idea if their baby fits the description," says Dr. Karp.

How to nurture:

Fortunately, all babies are born with a calming reflex, and it's relatively simple to activate, says Dr. Karp. He recommends the five S's: swaddling (wrapping your baby snugly in a blanket), side-positioning (holding him on his side), shushing (using a white-noise recording or machine, or simply making a "shh" sound), swinging (rocking him rhythmically), and sucking (offering him your breast, a bottle, or a pacifier). You'll need to experiment to see which of these techniques works best for your baby, but combining a few will usually work, says Dr. Karp.


How much is nature?

If your child still isn't sleeping through the night or takes super-short naps, you might be able to blame her genes in part. A study published in Pediatrics comparing identical twins and fraternal twins (who, on average, have only half their traits in common) found that genetics seems to play a role in the length of time babies sleep without interruption. Nearly all identical twins shared a tendency to wake up during the night, compared with less than 80 percent of fraternal twins. Researchers also found that identical twins are more likely to share similar napping patterns.

How to nurture:

One possible solution for a baby who doesn't sleep soundly at night: Go out together more frequently in the afternoon sunlight. Researchers at Liverpool John Moores University, in the U.K., found that infants who were reliable nighttime sleepers were exposed to significantly more daylight than poor sleepers. An afternoon stroll exposes babies to "environmental light," which helps regulate their sleep-wake schedule. (Make sure you avoid direct sunlight, which can be harmful to a baby's delicate skin and eyes.)

A few simple tweaks in your child's bedroom setup can also improve her sleeping habits. Buy blackout shades (since light can distract a baby during naptime as well as early in the morning), and make some noise too. "Playing a CD or a download of white noise all night long helps babies sleep better," says Dr. Karp. Keeping the sound at what he terms "the level of a soft shower" simulates the low-pitched rumbling your child heard in the womb.

Learn about four different parenting styles to see which one fits with your philosophy.

Stephanie Rausser/Trunk Archive

More Nature vs. Nurture Tips


How much is nature?

If your baby is constantly in motion, she may have been born that way. In their landmark New York Longitudinal Study, child psychiatrists Alexander Thomas, M.D., and Stella Chess, M.D., concluded that active infants are more likely to grow into energetic adults, while "relaxed" babies tend to remain relatively sedentary as they get older.

How to nurture:

Whether they tend to be couch potatoes or movers and shakers, all babies need regular opportunities to work the muscles that will enable them to roll over, sit up, crawl, stand, and eventually walk, run, and jump. "Get a variety of baby-safe objects that your child can grab, hold, shake, chew, and throw," suggests Peter Vishton, Ph.D., a professor of psychology at the College of William & Mary, in Williamsburg, Virginia.

You should also place your child on her belly regularly as early as possible (on a firm surface), even if she protests. "While putting an infant to bed on her back is important to prevent SIDS, she needs tummy-time sessions during the day so she learns to explore and move by lifting her head and pushing her hands down on the floor," notes Lorraine McCune, Ed.D., a professor in the department of educational psychology at Rutgers University, in New Brunswick, New Jersey.


How much is nature?

Is your baby shy around strangers, a natural flirt, or somewhere in between? Whatever the case, genetic factors may be at play. In their study, Drs. Thomas and Chess concluded that a baby's inherent temperament tends to determine whether he's social or aloof toward others. Need further evidence? A study in the journal Developmental Psychology found that adopted babies whose birth mother described herself as introverted tended to be the same way.

How to nurture:

Babies who tend to be outgoing by nature don't need much encouragement. However, if your child is reserved you can help him become more comfortable around other people by arranging regular get-togethers with extended family members and friends and playdates with other babies. Avoid pushing your little one to interact. "Try to be sensitive to your child and his reactions," cautions David S. Moore, Ph.D., director of the Claremont Infant Study Center at Pitzer College, in Claremont, California. Leaving a shy baby in the lap of someone he doesn't know might make him even more leery of unfamiliar people and situations. Give him as much time as he needs to warm up to them. You should also prepare your child for situations in which he'll be meeting someone new. "Talking to your 1-year-old about an upcoming visit with Aunt Cathy and showing him pictures of her can make the event seem less scary for him," says Parents advisor Jenn Berman, Psy.D., author of SuperBaby: 12 Ways to Give Your Child a Head Start in the First 3 Years. If he still bawls when she walks in the door, don't worry. Eventually your baby will become more at ease around others.


How much is nature?

Even before you introduce solids, you may notice that your infant has quirky feeding tendencies. Some babies gulp down breast milk or formula, while others sip slowly or take frequent breaks. Convinced your voracious child may grow up to be a gourmand? You could be right. Genetics plays a role in the speed at which a baby eats and also in his ability to recognize when he's full. And if your child spits out the sweet potatoes or peas you put in his mouth, heredity helps explain some of that as well. A study among identical and fraternal twins published in The American Journal of Clinical Nutrition concluded that the fear of trying unfamiliar foods is primarily genetic. Researchers suspect that some fussy eaters may be "supertasters," meaning they have a heightened sensitivity to bitterness that "nontasters" don't have.

How to nurture:

For a baby who balks at unfamiliar foods, there are several strategies for expanding his palate. "Turn meals into a highlight of your baby's day, a time for having fun together," suggests Eileen Behan, R.D., a dietitian and author of The Baby Food Bible. Even if his eating times don't coincide with yours, have a snack when you sit down with him to create a shared experience.

When introducing a new food, gently offer a little taste. If he refuses, try the next time (and the next) until he finally opens wide. If your child gags or spits out the food, take it away. But don't mistake a funny face or a grimace for disgust. These are perfectly normal baby reactions to novel experiences. "The more you expose a child to something new," notes Behan. "The more likely he is to taste it, especially if you pair the food with one of his favorites."

Originally published in the June 2014 issue of Parents magazine.

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