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6 Weird Baby Questions—Answered

Why does a baby's first head of hair fall out?

Basically, for the same reason you find yourself shedding like a Saint Bernard after giving birth: a drop in hormones. "High estrogen levels in your body during pregnancy cause both your and your baby's hair to grow, with less resting or shedding," says Jennifer Shu, M.D., an Atlanta pediatrician and coauthor of Heading Home With Your Newborn. Post­par­tum, your estrogen levels plummet -- and so do your baby's because he's no longer getting his hormones from you.

You both enter a shedding stage called "telogen effluvium." This lasts about six months for your baby, possibly longer for you. Will your child become as bald as Bruce Willis? It depends on his hair's texture and whether he sits up early (then he won't spend as much time rubbing his head against mattresses and activity mats). All the while, though, new hair is sprouting. Just don't be shocked if this do is way different -- most infants' second headful is darker and coarser.

Is having a baby painful for other animals?

Since most mammals don't bellow during labor (except for us and a few others, such as Sumatran rhinos), it's easy to assume they're not in pain. But, says Terri Roth, Ph.D., a reproductive physiologist at the Cincinnati Zoo, "it just isn't to their advantage to make a big production. They're trying to stay quiet and hidden, especially from predators." Our animal sisters are suffering, though.

Consider dogs. The first time they give birth, they're often in such pain that they have to be stopped from biting their emerging puppies, says breeder Donna Pitt of Newport, Virginia. Most other mammals, from guinea pigs to giraffes, will pace, lie down and get up repeatedly, and be unable to sleep when delivery is imminent, Roth says. Some paw the ground. "Eventually they start straining when they go into labor. You can see their hind legs stretch out behind them, and the muscles on their sides contracting," she explains. The only mammals that seem to escape this ordeal are those whose newborns are tiny and presumably slip out easily -- bears and kangaroos, for instance. (Lucky them.)

And how about birds? Could laying an egg -- in some cases one a fifth the mom's size -- hurt, too? You bet. Most birds breathe hard while laying; their bills open and shut and their tails bob, says Roth's colleague David Oehler, an ornithologist. Afterward, they enter a motionless "recovery phase." (During which, presumably, they're pining for a little Tylenol.)

What makes a baby's eyes change color?

Your infant's peepers are a work in progress. At birth, they often don't contain enough of a brownish or yellowish pigment called melanin to show their final hue. In fact, blue or gray eyes (common in fair-haired newborns) have almost no melanin, says Dr. Shu. But during your baby's first 6 to 12 months, her irises -- the eyes' colored parts -- make more of it and darken. In some people, complete pigmentation doesn't occur until adulthood.

Babies with blue or gray eyes tend to have fair skin, which is good for absorbing vitamin D from sunlight and building healthy bones. On the other hand, people who have darker eyes and darker skin are less likely to develop melanoma. Plus, Dr. Shu says, "they usually have higher levels of folate in their bodies, which helps maintain healthy red blood cells, nerves, and muscles."

How come I smell that diaper and my husband doesn't?

He probably isn't faking (at least not every time). "Women generally have a more acute sense of smell than men and can better distinguish between different odors," says Vitaly Vodyanoy, Ph.D., a professor of physiology at Auburn University, in Alabama. One thing women smell better is skatole, a key component of the odor of poop, according to research at Cardiff University, in Wales. Hormones may play a part in all this: During ovulation and pregnancy, when estrogen levels rise, so does your sniffing superiority. But, hey, Dad can still be trained to detect a full diaper by its appearance (and weight!).

How likely is my baby to get my dimples or my husband's cleft chin?

Scientists have found a dazzling array of traits that can be determined by a single gene and run "dominant" -- meaning that if you or your spouse has one, your baby could have up to a 50 percent chance of getting it, too. Besides dimples and clefts, the list includes widow's peaks, the ability to curl your tongue, unattached earlobes (as opposed to attached ones), extreme joint flexibility, and second toes that are longer than "big" toes. Still, just because you've got cheeks like Kirsten Dunst's or a chin like Ben Affleck's, your kid may not have a fifty-fifty shot at following suit, says Emily Lisi, a genetic counselor at the Johns Hopkins University Institute of Genetic Medicine, in Baltimore. His chances go way down if you have a "complex" version of the trait, guided by both genes and environment. How can you tell? If your own mom or dad also has the trait, and inherited it from a parent, then you can be pretty sure it's the dominant form.

Why is pink for girls and blue for boys?

Today's color "rules" are relatively new. "All babies wore white for the longest time because it was easy to boil and sanitize," says Jo Paoletti, Ph.D., a historian at the University of Maryland, in College Park. In the early 1900s, colored clothes became less of a hassle with the arrival of better detergents, dyes, and washing machines. Still, today's custom emerged gradually (as recently as the 1960s, John F. Kennedy, Jr., was photographed in a pink romper). Thanks to a rise of philosophies that we should "teach" gender, parents became eager for a color code. Newer, more delicate pinks may have struck moms and dads as more feminine; blue-for-boys may have gotten help from nursery rhymes such as "Little Boy Blue."

How come little kids wiggle so much in their sleep?

Does your child wedge herself sideways in her crib or do a complete 180 by morning? A possible reason: Infants and young kids move much faster through the various sleep stages than we do and often wake briefly at the end of each, says Judith Owens, M.D., director of the Pediatric Sleep Disorders Clinic at Hasbro Children's Hospital, in Providence, RI. This means they have more awakenings than an adult -- during which they might flip around like a pancake.