Wednesday, July 22, 2009

Vestigial Characteristics: Monkey Features of the Human Newborn

Newborn babies arrive with some pre-installed software and hardware that demonstrates, beyond a shadow of a doubt, our primate heritage.

Vestigial features like Darwin's point (see post below) evoke the pointed ears of Old World Monkeys — the ancestral line of nonhuman primates from which human primates descended. Old World Monkeys have pointy, Spock-like ears. You can see them perfectly in the photo of the baby saki monkey at the right.

The ears of Baby Field Notes have this point, named after Darwin because he was the first to observe and write about it. The arrow in the photo shows where she also has a tuft of hair growing from her ears. Right now the hairs are about 1/2 centimeter long. Like the hair growing on her shoulders, this hair will thin out with age.

Perhaps you can feel a small bump along the rim of your ear. Feel along. Not everyone has one that is pronounced and if so, it is often only present on one side. That little bump is a relic of your ancestors' descent from monkeys. So is the shoulder hair and ear hair of the newborn human primate.

In fact, humans are just as hairy as other primates, including other apes. We have just as many hairs per square inch as chimps, gorillas, bonobos and orangutans. Ours are just so fine and so short that they appear to be invisible, thus giving humans their 'naked ape' label. We're not really naked and hairless at all. Look closely at your skin under good lighting the next time you get out of the shower and you'll see what I mean. Our faces are hairy too.

As for pre-installed software, newborns have a number of reflexes that would clearly have been evolutionarily advantageous. One, the Palmer grasp, wold have been useful for grasping onto mom's hair in an emergency if she had to move abruptly. Newborns can actually support their own weight with it. I am not willing to experiment with BFN, but you can see in the following video exactly how impressive this reflex is.

Palmer Grasp Reflex

The Palmer grasp can be seen in human newborn feet as well.

The Moro reflex is another reflex useful for keeping baby with mom when she moves. Other primates occasionally hold their babies when they move, but for the most part, nonhuman primate babies latch onto mom's hair on their own and can stay in contact with her while she moves even when mom doesn't provide support. Humans retain these reflexes in spite of not being able to take advantage of them. They are atavistic, vestigial traits. These reflexes, like the presence of a nonfunctional appendix, illustrate that not every trait that is a product of evolution has a function in its present form.

Moro reflex


Paula Pindroh said...


I'm still a bit bummed that I don't have any sign of a Darwin's point :~/

Congrats on your little bundle of primate evolution! :~D


I had been wondering about that little bump I see on the top ridge line of everybody's ears, including mine!

Ms Avery said...

Very interesting!

Becky said...

Wow, that's really interesting. I hadn't heard any of that before, but it was fun to watch the videos and see the babies' reflexes in action. I actually might try the Palmer grasp on Little Miss...once she decides to arrive.