The Babinski Reflex, Speculation on its Evolutionary Adaptations.

The Babinski reflex is is a reflex in newborns characterized by: “Toes fan out and curl as foot twists in.”(the book, 7th edition, table 4.1) I would like to note that his is a reflex composed of 3 distinct actions. What if each action, were actually separate reflexes, each serving a separate purpose, though they co-occur?

Here are 2 videos that illustrate aspects of the reflex.

and then another video that characterizes the “curl” of the toes to be a plantar grasping reflex, similar to the plamar grasping reflex.

In relation to these videos, it is easy to see that a curling of the toes, could easily be explained with the same reasoning that the palmar reflex can be explained. It was at one time, adaptive to hold onto things with our feet, be it mother, or a tree branch.

Separating, or “fanning the toes” as a reflex could have been adaptive as a reaction to something beginning to slip though our finger-toes. Or it could be a stabilizing action, since fanned out toes would provide a wider base to stand on, then otherwise.

Perhaps this “foot twisting in” is an adaption similar to the rooting reflex that enables a baby to better find a foothold, one that is so close, they brushed against it with the sole of their feet. It may be significant to note, that when climbing or hugging to a surface, touch is one of the most important senses.  The rest of the senses are in the head, and if you are clinging on for dear life, Your head’s range of motion are limited(you don’t have eye’s on your toes). You have feel around with your foot for a better grip, or hold or whatever you want to call it. Thus, any transitive stimulus on the foot could signify a stable foot hold. A foot twisting in would be best suited for holding onto long thin cylindrical objects like trees, tree branches, or arms and legs of parents.  (this would be aided by the startle reflex, which would increase the likely hood that their arms would be wrapped around such a cylinder, thus providing additional support/grip.)

The 3 parts would work together like this: baby has a firm grasp on mother’s furry back. Mother changes position, thus baby is shifted and looses footing. The stimulus as the feet slid down mother’s back would be similar to what triggers the Babinski reflex. Fanning the toes gives more contact with hair to grip. The curl results in griping the hair like the palmar reflex, and then the inner twist is adaptive if the baby slides as far down as a leg. Twisting both feet inward would provide the optimum position for the feet, in order to grip a roughly cylindrical object positioned between the legs.

I have searched diligently for sources to support or disprove my speculation, including studies regarding a Babinski reflex in newborn primates, (tree dwelling, or ground based) or a reflex analogues to it. I have also searched for articles that presented a discussion of proposed theories explaining the Babinski reflex, or even one article enumerating just one theory. I found only one such source:

Fay, Temple. The Probable Origin and Purpose of the Superficial Reflex, Known as the Sign of Babinski. Its either in Confinia Neurologica 1955; 15: pages63-68, or its in “Stereotactic and Functional Neurosurgery” volume 15, No 1, 1955. The title seemed provocative.  I attempted to find a free edition in the Marriott article\journal database, and was unsuccessful. Here is the link to the site:

As of now, I am still entirely unaware of any debate, past or present regarding the Babinski reflex. I don’t even know if there has ever been a formal debate with competing explanatory theories.

By: Stuart Walker

~ by havok43v3r on September 16, 2009.

5 Responses to “The Babinski Reflex, Speculation on its Evolutionary Adaptations.”

  1. I have long held the theory that this reflex is left over from our time as primates (if you believe Darwin’s theory). This post is very interesting. Perhaps the fan out of toes is used to strengthen the toes by using the muscles, also from our time of needing to grab tree limbs for support… not sure on that one, but I suspect this is a primitive reflex.

  2. As we discussed the babynski Reflex in class, I really value this post. I seemed unsure as to what it really meant and that of it’s accuracy. I did speculate the comparison between the grasping of fingers reflex with regard to the Babynski Reflex. It seems that it could be similar in that essentially we seem to react to feeling and touch, whether comforted and/or startling! Accordingly, I wonder how much infants make sense of fear, comfort, and etc. feelings.

    Zach Rusk

  3. I am getting at this: the babinski reflex doesn’t make sense becuase we are too far removed from the conditions where it did make sense. a discussion of evolutionary adaptation is always reconstructive and based on hundreds of assumptions including that the reflex exists because at one time it was instrumental in survival. One goes back in time so to speak, and imagines under what conditions the babinski reflex would be adaptive. one could also assume, that if the reflex doesn’t do anything, it will eventually disappear, so the babinski reflex may have been stronger and more developed back when it was adaptive(it make look different).
    AS far as accuracy goes, I never claim to have the inside scoop. I even admit I have no idea of legitamate current speculation on the topic. Evolutionary psychology is as much about telling a reasonable story as finding evidence. My post was about telling an evolutionary story.
    It is entirely possible that the Babinski reflex is a wild card thrown in my nature. note my following story>>> babies that had reflexes that served a purpose, also possibly had random reflexes that served no purpose(since variations are random to begin with), but because these babies with reflexes were more likely to survive to reproduce, the random reflexes are passed on with the legitimate reflexes, to the next generation.
    there you have it: a type of heritable reflex that at no time was adaptive. Both could explain the presence of the Babinski. this is where evidence comes into play. do any other species have a similar reflex? does the reflex serve a purpose in other species? How far removed are these other species from us? the story becomes more believable with evidence, and good evidence.

    Once again, I have no real evidence. join me in my speculation! Anyone else want to come up with a story explaining the babinski reflex?
    Stuart Walker

  4. Cool. Thanks for the info!

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