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6 Surprising Examples of Human Vestigiality

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People have speculated over the nature of seemingly useless physical characteristics in living things for thousands of years. It wasn’t until the late 18th and early 19th centuries, though, that the idea of vestigiality would enter the public imagination via the writings of a couple of French naturalists and pre-emptive Darwinists, Étienne Geoffroy Saint-Hilaire and Jean-Baptiste Lamarck. Darwin would, of course, go on to redefine the field of human biology some half-century later with On the Origin of Species, but it was his second book, 1871’s The Descent of Man, where he listed a number of the structures we know today as vestigial for the first time, among them the appendix, tail bone, and wisdom teeth.

The German anatomist Robert Wiedersheim ultimately coined the term in his 1893 book The Structure of Man: An Index to His Past History, including 86 organs believed to be the “vestiges” of human evolution. We now understand a number of those from the Wiedersheim list to be vital (i.e., the thymus and pituitary gland), but others have emerged to take their place. Here are six of the more surprising examples of human vestigiality.


Known medically as cutis anserina, goose bumps (so dubbed for the skin’s resemblance to a plucked goose) are triggered reflexively by a range of stimuli, including fear, pleasure, amazement, nostalgia, and coldness. The mechanism that causes the reaction, piloerection, triggers the tiny muscles at the base of each body hair to contract, eliciting a tiny bump. The reflex played a crucial role in the fight-or-flight response of our human evolutionary ancestors, who were covered in body hair: The standing hairs could make primitive man appear larger to predators, perhaps averting the threat. When unprotected and faced with cold, goose bumps would act as added insulation, raising the hair up to create an extra layer of warmth. Though piloerection remains a useful defense for many animals (think of an annoyed porcupine or cornered cat), humans, having long ago shed the bulk of our body hair, retain it almost exclusively as an emotional response.


This term refers to portions of our human genome for which no functional role has been discovered. Though controversial, many scientists believe that much of our DNA exists simply as remnants of some purpose long past served. Among the sequences of DNA in our bodies, a good portion of those have traces of genetic fragments called pseudogenes and transposons, indicating a defect in the strand that could’ve been caused by a virus or some other mutation incurred in the course of our evolutionary history. Like any vestigial structure, we retain pieces of this genetic material because it really isn’t causing any trouble: Century after century, the “junk” sequence is duplicated and passed on, even if it no longer has a use.


This tiny fold of skin in the corner of the eye is a vestige of the nictitating membrane—essentially, a third eyelid from a time when we needed something like that. Still present in birds, reptiles, and fish, the fully functioning structure is translucent and draws across the eye lengthwise both for protection and to keep the surface moist while retaining sight. At some point primitive humans lost the use for it, but retained a small piece along with its associated muscles (also vestigial). The semilunaris is one of a handful of vestigialities that are more pronounced or prevalent in certain ethnic groups—in this case, Africans and Indigenous Australians.


As we’ve evolved, having to rely less on our physicality, a number of muscles throughout the body have lost utility, though many of us still have them. This category of vestigiality is heavily determined by ethnicity. The occipitalis minor, for example, is a thin, banded muscle at the base of the skull that functions to move the scalp. Exhibiting a wild geographical variance, all Malays are born with it, half of all Japanese, and a third of Europeans, but it’s never present in Melanesians. The occipitalis joins to the auricular muscles, which once allowed us to move our ears to better hear predators, but are now pretty much nonfunctional.

Other vestigial muscles include the palmaris longus, the ropey tendon that tenses in the bottom wrist when you clench your hand; the pyramidalis in the abdomen, which 20 percent of all humans lack; and the plantaris in the leg, which still aids slightly in knee flexion, but whose contribution is so trivial that it's become better known as a tendon which surgeons commonly remove to graft into other areas of the body compromised by injury.


If there’s one thing babies are good at, it’s squeezing your finger when you place it in their hand (one early study demonstrated how strong the grip can actually be). Though we do this primarily as a way to engage, the child is simply reacting to an evolutionary stimulus. When we were still covered in body hair, an infant would have used this reflex to cling to its mother’s coat. This provided useful for portability and, in the case that danger had to be evaded, not having to carry the child left the mother with both hands free to escape, maybe by climbing a tree. The reflex is also active in the feet, noticeable in the way an infant’s feet curl in when sitting, but both reflexes usually disappear around six months.


Let’s call our sense of smell vestigialish. Though we obviously still use it every day, its function and role in humans is greatly reduced from what it once was. Animals with the most acute sense of smell are those that still rely on it for tracking food, avoiding predators, or for mating purposes. Since we now have grocery stores, no natural enemies, and OkCupid, olfaction is more of a trait of convenience at this point (though there is evidence that pheromones may play a role in human interaction). Unlike the other examples on this list, the ability to smell can still aid in survival, though, by alerting you to a toxicity that’s otherwise invisible, such as a gas leak.

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Name the Author Based on the Character
May 23, 2017
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