CLOSE
Thinkstock
Thinkstock

6 Surprising Examples of Human Vestigiality

Thinkstock
Thinkstock

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.

1. GOOSE BUMPS

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.

2. JUNK DNA

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.

3. PLICA SEMILUNARIS

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.

4. MUSCLES

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.

5. PALMAR GRASP REFLEX

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.

6. OLFACTION

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.

nextArticle.image_alt|e
iStock
arrow
science
Scientists Accidentally Make Plastic-Eating Bacteria Even More Efficient
iStock
iStock

In 2016, Japanese researchers discovered a type of bacteria that eats non-biodegradable plastic. The organism, named Ideonella sakaiensis, can break down a thumbnail-sized flake of polyethylene terephthalate (PET), the type of plastic used for beverage bottles, in just six weeks. Now, The Guardian reports that an international team of scientists has engineered a mutant version of the plastic-munching bacteria that's 20 percent more efficient.

Researchers from the U.S. Department of Energy's National Renewable Energy Laboratory and the University of Portsmouth in the UK didn't originally set out to produce a super-powered version of the bacteria. Rather, they just wanted a better understanding of how it evolved. PET started appearing in landfills only within the last 80 years, which means that I. sakaiensis must have evolved very recently.

The microbe uses an enzyme called PETase to break down the plastic it consumes. The structure of the enzyme is similar to the one used by some bacteria to digest cutin, a natural protective coating that grows on plants. As the scientists write in their study published in the journal Proceedings of the National Academy of Sciences, they hoped to get a clearer picture of how the new mechanism evolved by tweaking the enzyme in the lab.

What they got instead was a mutant enzyme that degrades plastic even faster than the naturally occurring one. The improvement isn't especially dramatic—the enzyme still takes a few days to start the digestion process—but it shows that I. sakaiensis holds even more potential than previously expected.

"What we've learned is that PETase is not yet fully optimized to degrade PET—and now that we've shown this, it's time to apply the tools of protein engineering and evolution to continue to improve it," study coauthor Gregg Beckham said in a press statement.

The planet's plastic problem is only growing worse. According to a study published in 2017, humans have produced a total of 9 billion tons of plastic in less than a century. Of that number, only 9 percent of it is recycled, 12 percent is incinerated, and 79 percent is sent to landfills. By 2050, scientists predict that we'll have created 13 billion tons of plastic waste.

When left alone, PET takes centuries to break down, but the plastic-eating microbes could be the key to ridding it from the environment in a quick and safe way. The researchers believe that PETase could be turned into super-fast enzymes that thrives in extreme temperatures where plastic softens and become easier to break down. They've already filed a patent for the first mutant version of the enzyme.

[h/t The Guardian]

nextArticle.image_alt|e
Ian Cartwright
arrow
Stones, Bones, and Wrecks
An 88,000-Year-Old Middle Finger May Change What We Know About Human Migration
Ian Cartwright
Ian Cartwright

A middle finger might change what we thought we knew about human migration from Africa. As Gizmodo reports, a new study in Nature Ecology and Evolution analyzes what may be the oldest modern human fossil outside of Africa and the Levant (modern-day Israel, Lebanon, Syria, and Jordan). Found in an ancient lake bed in the Arabian desert, the bone has been dated to 88,000 years ago, indicating that human migration from Africa may have started much earlier than previously thought.

Previous research has suggested that Homo sapiens populations migrated out of Africa and into Eurasia (perhaps thanks to climate change) in one big wave around 60,000 years ago. The fossilized finger bone, about an inch long, indicates the story might be more complicated.

A paleontologist with the Saudi Geological Survey, Iyad Zalmout, found the bone in 2016. He and his fellow researchers created 3D scans of the bone and compared them with other finger bones from Homo sapiens, Neanderthals, and modern primates like gorillas to determine that it is, in fact, a human bone. They then dated the fossil using uranium series dating, a measure of the bone's ratio of radioactive elements, to arrive at an estimated age of roughly 88,000 years old. They also found animal fossils and sediment at the site to be around 90,000 years old.

A surveyor stands in the desert.
The area in Saudi Arabia where the finger was found.
Klint Janulis

At that time, the area in the Nefud Desert where the bone was found would have been semi-arid grasslands surrounding a freshwater lake, a more hospitable climate than it is today. At some parts during this era, the Red Sea between Africa and the Arabian Peninsula would have been low enough to make it essentially just a big river, so humans could have crossed there, as a related article in the journal by anthropologist Donald Henry notes.

Several scientists told Gizmodo that it's possible that the bone isn't human at all—it could belong to a relative of Homo sapiens—and that the authors of the new study are overstating the significance of their finding, so the analysis is somewhat controversial.

However, other evidence has pointed to an earlier African exit date for humans. In 2015, scientists in China discovered human teeth they dated to 80,000 years ago, though they weren't able to date the bone directly—instead, they analyzed the teeth's surroundings. In January 2018, scientists announced that they had found a partial jawbone in an Israeli cave dating back at least 177,000 years.

"The ability of these early people to widely colonize this region [of Arabia] casts doubt on long held views that early dispersals out of Africa were localized and unsuccessful," said lead author Huw Groucutt, of the University of Oxford and the Max Planck Institute for the Science of Human History, in a statement.

[h/t Gizmodo]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios