Parents of newborns are just as curious as the babies they raise. No doubt pediatricians are flooded with question like why babies make a mess of their food, why they cry without any apparent motive or laugh uncontrollably over the slightest gesture. But why babies make fists? Well, that one isn't usually brought up, but it's a head-scratcher nonetheless.
"They never ask because we see it so commonly," said physician William Adams who has his own theory on the topic. "It's just what babies do. I've thought about it, and I wonder if it's more important than we think."
Back when he was a med student, Adams asked the very same question and got the same response: the palmar grasp reflex. It's an involuntary muscle action that starts to appear in the fetus around the third month of pregnancy and is widely interpreted as a way for a baby to develop its hand muscles for grasping objects after birth.
It's one of the more powerful muscular developments going on while the baby's still in the fetus. That's particularly evident when a newborn wraps its hand around a parent's finger and tightens its grasp when the parent tries to remove it. Or when a baby is lifted up with the tyke's fingers clinging to the parent's fingers.
But Adams has another theory for the reflex, after making note of another involuntary action, namely when the baby tucks its thumb into its fist.
He concludes that it's not so much about the baby, but the amniotic sac inside the mother which incubates the fetus. It's a layer that is critical to development because of the biochemistry it contains for nurturing. But the sac is paper-thin, which makes the membrane vulnerable to punctures. In fact, piercing it is one common method doctors use to bring on premature births.
But when a baby starts developing fingernails in utero, its arm movements run the risk of breaching that membrane. So do toenails, given how common it is for a fetus to kick against the womb. But a newborn's toenails don't grow outwards like fingernails, so a punted sac remains safe before birth.
That's when Adams deduced that the involuntary fist reflex develops in the baby as a way to protect the amniotic sac from scratches. Via reflexes that result in a fist with fingers and the thumb tucked within the palm, the fetus can pound all its wants and the sac is safe from any uppercuts, jabs, or haymakers.