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!  I took this one about three days later, showing the grasping reflex of the pedal extremities: 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:
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. Newborn (infant) reflexes NCLEX questions quiz for nursing students! For exams, you want to be familiar with newborn reflexes. Newborns are born with reflexes (sometimes referred to as primitive reflexes) that help them survive the first months to year of life. These reflexes include: rooting, suck, palmar grasp, Babinski, plantar grasp, tonic neck, crawling, step, and Moro reflexes. Therefore, when studying these reflexes you want to be familiar with:
(NOTE: When you hit submit, it will refresh this same page. Scroll down to see your results.) Newborn Infant Reflexes NCLEX Nursing Quiz Questions1. During an assessment of an infant, you note that when the infant’s head is turned to the right side, the leg and arm on the right side will extend, while the leg and arm on the left side will flex. You document this as what type of reflex? A. Rooting Reflex B. Sucking Reflex C. Moro Reflex D. Tonic Neck Reflex The answer is D. When the infant’s head is turned to a particular side, the leg and arm on that side will extend, while the leg and arm on the opposite side will flex. 2. Select the option below that best describes how to assess the palmar grasp reflex: A. Stroke the cheek of the infant and assess if the head turns toward the stimuli. B. Stroke the sole of the foot starting at the heel to the outward part of the foot and assess if the big toe bends back and the other toes spread out. C. Hold the infant upright with the legs and feet touching a surface and assess if the infant will move the legs in a stepping motion. D. Stroke the inside of the infant’s hand with an object and assess if the hand closes around the object. The answer is D. Stroking the inside of the infant’s hand with an object and assessing if the hand closes around the object helps assess the palmar grasp reflex. 3. You note that when a finger is placed under the toes of a newborn, the toes will curl downward. This is known as the __________? A. Babinski reflex B. Plantar grasp reflex C. Tonic Neck reflex D. Step reflex The answer is B. This is known as the plantar grasp reflex. 4. When the Moro Reflex is stimulated in an infant, the infant will _____________the arms with the palms of the hands turned ___________ and then move the arms ___________ the body. A. flex, upward, away from B. extend, upward, back to C. flex, downward, back to D. extend, downward, away from The answer is B. When the Moro Reflex is stimulated in an infant, the infant will EXTEND the arms with the palms of the hand turned UPWARD and then move the arms BACK TO the body. 5. When does the sucking reflex in an infant disappear and become voluntary? A. 6 months B. 2 months C. 4 months D. 12 months The answer is C: 4 months. The sucking reflex in an infant will disappear and become a voluntary function at about 4 months of age. 6. In a 3-month-old infant you assess the Babinski Reflex. What is the appropriate response in an infant at this age? A. The big toe plantar flexes and the other toes curl downward. B. All the toes curl downward. C. The big toe dorsiflexes and the other toes spread outward. D. The big toe plantar flexes and the other toes fan outward. The answer is C. The Babinski reflex should disappear around 1 year of age. However, in an infant this age the big toe should dorsiflex (bend back) and the other toes spread outward. 7. You note when a 2-month-old is held upright with the legs and feet touching the surface, the infant will appear to be walking on the surface. This reflex is called the? A. Bauer Crawling Reflex B. Push-to-Walk Reflex C. Babinski Reflex D. Step Reflex The answer is D. This is known as the step reflex. 8. The nurse wants to assess the crawling reflex in a newborn. How is this reflex assessed? A. The nurse places the infant in the prone position and applies pressure with the hand to the sole of the foot. In response, the infant should attempt to push against the hand and move the arms and legs in a crawling like motion. B. The nurse places the infant in the supine position and applies pressure with the hand to the sole of the foot. In response, the infant should attempt to push against the hand and move the arms and legs in a crawling like motion. C. The nurse places the infant in the prone position and applies pressure with the hand to the neck. In response, the infant should attempt to move the arms and legs in a crawling like motion. D. A. The nurse places the infant in the supine position. In response, the infant should attempt to lift the head and move the arms and legs in a crawling like motion. The answer is A: The nurse places the infant in the prone position and applies pressure with the hand to the sole of the foot. In response, the infant should attempt to push against the hand and move the arms and legs in a crawling like motion. Don’t forget to tell your friends about this quiz by sharing it your Facebook, Twitter, and other social media. You can also take more fun nursing quizzes. *Disclaimer: While we do our best to provide students with accurate and in-depth study quizzes, this quiz/test is for educational and entertainment purposes only. Please refer to the latest NCLEX review books for the latest updates in nursing. This quiz is copyright RegisteredNurseRn.com. Please do not copy this quiz directly; however, please feel free to share a link to this page with students, friends, and others. |
The ________ reflex explains why newborns hold on tight when you put a finger in their hands.
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