In honor of reaching 800 posts, we’ve taken a look back at our most popular pieces. Some of them have been surprises–like Do Black Babies Have Blue Eyes? (I didn’t think they did, but I wanted to be sure, because I had run across general claims like “All babies are born with blue eyes.”)
Apparently people love babies, so here are some interesting baby facts:
Babies are born with less melanin than their parents, because there’s no need for protection from sunlight while in the womb. This is why black babies are often a bit paler than than parents. (I try not to invade other people’s privacy by posting photos of other people’s infants, but here is a stock photo in which the newborn’s color is about the same as their father’s palms, distinctly lighter than their father’s overall coloration.)
Melanin levels typically increase over time in babies of all races, darkening skin and eyes. So white babies are often born with blue, grey, or light brown eyes that darken to the normal white range of blue to dark brown, but most African and Asian babies start out with eyes that are already pretty dark because they naturally have more melanin–though even their eyes show a range of newborn colors, from dark grey to green.
Hair: Most babies, including black/African babies, are born with soft, silky hair. Baby hair is different from adult hair because it grows from round hair follicles (which produce straight hair) and lacks the central shaft (or medulla) that stiffens adult hair. Over the first few months of life, follicles flatten and medullas grow in, giving hair its stiffer, curlier, more adult form, though the extent of this process differs widely by population.
White babies end up with a variety of hair textures. Most Asian babies end up with thick, straight hair, due to a variant of the EDAR gene that arose about 65,000 years ago. Despite the great genetic variety found in Sub-Saharan Africa, almost all black babies end up with tightly coiled, curly hair. Black hair has probably therefore been very valuable to people in Africa, providing enough of an evolutionary advantage that it has become nigh universal.
(Note that our nearest human relatives, the chimps, do not have curly hair. It is tempting to say that infant hair resembles chimpanzee hair, but I have never petted a chimp and so cannot really judge.)
Interestingly, many facial expressions are universal–emotions like happiness, sadness, anger, and disgust are expressed similarly in people from Sub-Saharan Africa to New Zealand, from Norway to Argentina; in newborns and elderly [pdf]; in blind people and sighted.
What about differences between babies?
More science on reactivity differences in babies:
433 4-mo-old infants from Boston, Dublin, and Beijing were administered the same battery of visual, auditory, and olfactory stimuli to evaluate differences in levels of reactivity. The Chinese Ss were significantly less active, irritable, and vocal than the Boston and Dublin samples, with Boston Ss showing the highest level of reactivity. Data suggest the possibility of temperamental differences between Caucasian and Asian infants in reactivity to stimulation.
Pregnant ladies may be interested to learn that average gestation length varies by race/ethnicity:
The average length of gestation is about 5 days shorter in black populations than in white populations. Although some of this difference is accounted for by higher preterm delivery rates in blacks, the most common gestational week of delivery at term is the 39th in black populations, the 40th in white. Black gestational age specific neonatal mortality is lower than that of whites until the 37th week of gestation, but higher thereafter.
Another article with similar findings (though I don’t know how they define “Asian” because the source is British and Brits often include south Asians like Pakistanis in the “Asian” category even though they are genetically closer to Europeans. So far I haven’t found any data that specifically addresses gestation length in East Asians.) This study found that pregnancies vary naturally in length by over a month, even excluding some premature births. There are many reasons why pregnancies may vary, including maternal age, size, stress, and genetics–important factors for Obgyns to keep in mind when evaluating the medical needs of different mothers and their fetuses.
There’s a lot of variety in humans.