The grasping reflex of babies: a vestigial trait?

April 8, 2014 • 11:56 am

This is the type of post I originally intended to publish on this website, and the only type of post, for the website was created, at the behest of my editor at Viking/Penguin, to support my book WEIT. My idea then was to post a bit of cool evidence for evolution every few weeks or so. Then things got out of hand. . . But today we are back to the original mission.

One of the pieces of evidence I use for evolution, in both my book and my undergraduate classes, is the presence of vestigial traits. And there are some nice behavioral ones. I wiggle my ears for my students, which they love, but I do it to demonstrate our vestigial ear muscles, useless in modern humans but adaptive in our relatives, which can move their ears widely to localize sounds. (Check out your cat when it hears something.)

Humans have another vestigial behavior: the “grasping reflex” (also called the “palmar reflex”). Young infants can hold onto objects with both their hands and their feet—and hold tightly and tenaciously. They lose this behavior—which is instinctive, prompted by inserting a finger or a stick in their hands or feet—a few months after birth.

While we’re not 100% sure what it represents, I’d bet that it’s a genetic holdover from our ancestry as hairier primates. (Remember: we’re the only “naked apes.”) In primate species, the young are carried about by hanging onto their mother’s fur with both hands and feet, and they keep this behavior throughout infancy. Their ability to hold on is important for their survival.

Humans aren’t hairy, and aren’t carried about by clinging to their mother’s fur. But we still, at least for a short period, show genetically-based behaviors that testify to our descent from furrier creatures.

Here are some photos of the daughter of a friend. This one shows the grasping reflex at 7 days of age. Note that  she’s holding on so hard that her fingers are white!

7 days

I took this one about three days later, showing the grasping reflex of the pedal extremities:
Grasping reflex

For years I tried to persuade my friends who had infants to let them hang from broomsticks (I have a drawing of this behavior in an evolution textbook from the 1920s), so I could photograph it or make a video. But for some reason they always refused, even though I claimed that one can do this safely: just put the infant over your lap or a bunch of pillows. No dice.

But I was recently shown this video from the 1930s showing two infants “competing” to see who can hang the longest. Here are the YouTube notes:

Fragment of “Johnny and Jimmy” (twins), a silent film by Myrtle McGraw, recorded in 1932. from McGraw, M.B. (1975). Growth: A study of Johnny and Jimmy. New York: Arno Press. [1935]

One baby makes it for only 4 seconds (what a wimp!), but the other is still hanging after 37 seconds! I love the blotting out of the genitals.

Here’s a more recent video in which the infants are suspended more humanely. The genitalic blur has also been made spiffier: it’s now a fig leaf.

This isn’t the only primitive reflex displayed by human infants. Wikipedia has a whole list of them (the foot-closing is called the “plantar reflex”), and you might amuse yourself by speculating about which of them might have been adaptive in the infants of our ancestors, and why.

64 thoughts on “The grasping reflex of babies: a vestigial trait?

  1. Not to kid, but my wife can pick up stuff all over the house with her toes. *But not my socks?!?

    This is interesting. I often wondered why babies had these “grips of steel”; now I know!

    1. “my wife can pick up stuff all over the house with her toes.”

      So can I; I could also pinch the hell out of you.

    2. I do lots of stuff with my feet too. But it is due to conscious effort decades ago to develop foot skills for soccer (football), which then became habit. Not much grasping.

  2. Wouldn’t creationists argue that it’s a good thing for human babies to grasp whatever they could by whatever means they could to keep themselves from falling, and thus this is not a vestigial characteristic?

    1. That’s not a bad alternative idea except for one thing: human infants lose that grasping reflex shortly after birth, while primate infants keep it. Why lose it if it’s adaptive to keep you from falling? And, I suspect that infants of our early ancestors wouldn’t be faced with having to grab onto twigs and the like to save themselves.

      The key to its being vestigial is that its lost in early infancy.

      1. Yeah, I’d heard that new-born infants could support their own weight with this grip, so experimented on my firstborn (with wife’s permission) when he was a day old. But, disappointingly, it wasn’t a great success. He gripped my fingers and I could raise his torso well off the bed, but he couldn’t hold on the extent of having his whole body lifted into the air.

          1. Yup – one index finger in each hand. I don’t think his grip strength as a new-born was any different or special compared to when he was a couple of months old. Anyone who has had their hair grabbed and pulled by a baby will know it’s no easy task to gently disengage.

            Seems to me that they just lack that fine discrimination – anything they grab, they grab full-on.

            1. “Anyone who has had their hair grabbed and pulled by a baby…”

              Or dangling earrings! (Fortunately not me, but an acquaintance.)

    1. What is the evolutionary advantage that this gives you? Keeping flies away? I wonder why that wasn’t selected for in humans (those people who could wiggle their ears got fewer germs/disease).

      1. I’m a throw back to cats. It’s just a vestigial thing for when out ears were directional to hear stuff well like you see animals with prominent ears do today: horses, dogs, cats, etc.

      2. It enables accurate locating of sound sources. Similar to a method used with RDF antenna to locate an RF source, the ear / antenna is moved around until the orientation that results in the strongest signal is determined.

    2. So how does it work? If you wiggle both you fly in a straight line but if you only wiggle one you fly in circles? 😉

  3. As a baby, my cousin could not only ride on my aunt’s back by gripping her back hair, but would occasionally climb into her pouch for a nap.

    But seriously folks..
    This is a great post, Jerry. Now I’ve got to find some creationist friends whose Facebook walls need a new post.

    1. by back hair you mean the hair on her head that grows to a long enough length to lay against her back?

      1. Reminds me of a childhood love poem…
        Your hair flows down your back – not on your head.
        Your eyes are like pools – cesspools.
        et cetera, et cetera. 🙂

        1. Her eyes were like limpid pools of stingent darkness,
          She had a face only a mother could love,
          She was so bow-legged when she sat around the house, she really sat around the house

          Part of a ditty my departed grandfather used to entertain people with. Can’t remember any more of it. He was well known for being “a character.”

          1. I once found a piece of paper where my dad was testing a typewriter. It read, “Dear Sir, I do not want to marry your daughter; she has a face that would stop a train in its tracks”. 😀

            1. Were you a kid / teen when you found that?

              Was it one of those shocking realizations that your parents are actually much like you instead of some distant, alien, adult creature?

              1. I think I was a teen when I found it and I thought it was hilarious and I didn’t know that my dad would write something smart assed like that when there was no one to show it to (I would show everyone)


  4. “This is the type of post I originally intended to publish on this website, and the only type of post…to support my book WEIT”

    Really? I thought the original intention of this website was pictures of lolcats… 😉

    1. Well it did go off the rails pretty quickly. 🙂 I believe the book was published on January 22nd, 2009, and when I joined the website in February 2009 he was already into the cat posts. 😛

      1. We know male (and female?) foetus (4th declension Latin plural) have erections in the womb.

        Must be that “Original Sin” manifesting itself, eh? 😉

    1. Is there something about regular diapers that inhibit this particular behavior? Why are all the video examples of babies completely in the buff?

      (I’m not being serious, if anyone was wondering.)

  5. Associated with this is the very common act of an adult–or even a child–offering their finger to a baby so that the baby will grasp it. It seems like a nice way to introduce yourself to a new little one and have some contact with the baby, but I’ve often wondered if we are subconsciously performing a simple test of health and fitness on the baby as well…perhaps a simple test that was also performed by our extinct ancestors.

    1. I was thinking something like this too, could a newborn infant grasping help a bit with bonding with its new mother, and thus help it linger longer as a trait in humans?

    1. Because “they” are not “they”, and changing things (or babies) in the past is not as easy as you assume.

    1. Serendipitously, I read about cat kneading on the weekend. Some hypothesize it comes from before domestication when cats had to push down foliage. Others think it is from drinking milk. No one actually knows for sure.

      1. Hah! I’m sure it’s related to suckling. Just last week Larry the Cat got into my bed during the night and began kneading my shoulder quite vigorously (ouch – big cat, big paws, and long claws). Then he got quite carried away and started nibbling and sucking at my skin between his paws. The kneading was uncomfortable, but I was a bit creeped out at this and deposited him back on the floor.

  6. I think this ‘grasping’ reflex also occurs in older humans when balance is lost. In my view it also explains perfectly why one of the best and most common golf swing tips is to try and keep a constant grip pressure.

  7. I don’t understand why vestigial traits would be paraded out in developing babies and then disappear, as if The God of Evolution was illustrating for us from whence we came. It’s the “ontogeny recapitulates phylogeny” idea, which I thought was false.

    1. They don’t all disappear – I can still wiggle my ears & poor little kiwis have wings that you can’t even see.

      Also, that’s how things work. Evolution, as a process, cludges together things from what it has to work with (which isn’t to imply that evolution has a direction or that it is conscious).

      1. Well, you can’t see their wings until you part the bird’s feathers, that is 🙂

        Funnily enough they like to sleep with their beak tucked under one wing, tiny though it is – and have a preferred side.

        1. When I first saw a kiwi bird I was surprised at how big they were. I somehow thought they would be the size of starlings. My Nana made the same size mistake with squirrels when she visited Canada. She thought squirrels would be the size of cats.

  8. ..and why do we have fingernails? Toenails make sense, because we could drop stuff on our toes or stub our toes, but fingers are too high for that… when we’re standing up

    1. To peel fruit, scratch backs, crush parasites, scrape kernels from broken nutshells, and spread compressive loads across terminal finger joints for gripping and climbing. Just for a few.

  9. These vestigial reflexes are fascinating and serve as another line of evidence for mammalian connections and truth of evolution. In addition to the ability to wiggling my ears, I can move my scalp back and forth. Does the same muscle control both actions? Is the subcutaneous muscle used to move one’s scalp a vestige of well developed muscles used by ungulates to shoo away insects?

    1. I think it is the same group of muscles. I wish, save for the fact that shoes would be impossible to buy, I had prehensile toes. I’m so jealous of other apes & their feet hands!

  10. One possible vestigial trait that confuses me is sweaty palms when you have a fear of heights.
    I can understand tingling feet as though you’re trying to use the no longer existing opposable toes, but what possible evolutionary advantage is having sweaty palms when all you really want to do is grip onto something?

    1. One trait I can’t understand, & it isn’t vestigial, is throwing up when you’re dehydrated. Thanks body, puking more water is just what I needed when I need water! I suspect it’s the brain saying, “I feel woozy; maybe you ate some poisonous berries, here I’ll make you puke those up”.

  11. Reblogged this on peakmemory and commented:
    I often talk about the grasping reflex in my classes on developmental psychology and I am delighted that Jerry Coyne wrote this blog post on the subject. The great biologist Theodosius Dobzhansky famously wrote that “nothing in biology makes sense except in the light of evolution.” It is also true that nothing in developmental psychology makes sense except in the light of evolution

  12. As every mother, father, aunt, sister, friend, baby-sitter and nanny with long hair has experienced, as soon as a baby – even a newborn barely out of its mother’s womb – feels hair on its hand, it will grab and grasp it so tightly that it is difficult to pry the hair out of its hand and make it let go of it. I have seen mothers swim with very young babies holding on to their mother’s hair with both hands and hold their heads above the water – and loving it. The mothers in question had read the late Elaine Morgan’s book “The Descent of Woman” and adhered to the Aquatic Ape Theory.

Leave a Reply to whyevolutionistrueCancel reply