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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.

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.

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Scientists Study the Starling Invasion Unleashed on America by a Shakespeare Fan

On a warm spring day, the lawn outside the American Museum of Natural History in Manhattan gleams with European starlings. Their iridescent feathers reflect shades of green and indigo—colors that fade to dowdy brown in both sexes after the breeding season. Over the past year, high school students from different parts of the city came to this patch of grass for inspiration. "There are two trees at the corner I always tell them to look at," Julia Zichello, senior manager at the Sackler Educational Lab at the AMNH, recalls to Mental Floss. "There are holes in the trees where the starlings live, so I was always telling them to keep an eye out."

Zichello is one of several scientists leading the museum's Science Research Mentoring Program, or SRMP. After completing a year of after-school science classes at the AMNH, New York City high school students can apply to join ongoing research projects being conducted at the institution. In a recent session, Zichello collaborated with four upperclassmen from local schools to continue her work on the genetic diversity of starlings.

Before researching birds, Zichello earned her Ph.D. in primate genetics and evolution. The two subjects are more alike than they seem: Like humans, starlings in North America can be traced back to a small parent population that exploded in a relatively short amount of time. From a starting population of just 100 birds in New York City, starlings have grown into a 200-million strong flock found across North America.

Dr. Julia Zichello
Dr. Julia Zichello
©AMNH

The story of New York City's starlings began in March 1890. Central Park was just a few decades old, and the city was looking for ways to beautify it. Pharmaceutical manufacturer Eugene Schieffelin came up with the idea of filling the park with every bird mentioned in the works of William Shakespeare. This was long before naturalists coined the phrase "invasive species" to describe the plants and animals introduced to foreign ecosystems (usually by humans) where their presence often had disastrous consequences. Non-native species were viewed as a natural resource that could boost the aesthetic and cultural value of whatever new place they called home. There was even an entire organization called the American Acclimatization Society that was dedicated to shipping European flora and fauna to the New World. Schieffelin was an active member.

He chose the starling as the first bird to release in the city. It's easy to miss its literary appearance: The Bard referenced it exactly once in all his writings. In the first act of Henry IV: Part One, the King forbids his knight Hotspur from mentioning the name of Hotspur's imprisoned brother Mortimer to him. The knight schemes his way around this, saying, "I'll have a starling shall be taught to speak nothing but 'Mortimer,' and give it him to keep his anger still in motion."

Nearly three centuries after those words were first published, Schieffelin lugged 60 imported starlings to Central Park and freed them from their cages. The following year, he let loose a second of batch of 40 birds to support the fledgling population.

It wasn't immediately clear if the species would adapt to its new environment. Not every bird transplanted from Europe did: The skylark, the song thrush, and the bullfinch had all been subjects of American integration efforts that failed to take off. The Acclimatization Society had even attempted to foster a starling population in the States 15 years prior to Schieffelin's project with no luck.

Then, shortly after the second flock was released, the first sign of hope appeared. A nesting pair was spotted, not in the park the birds were meant to occupy, but across the street in the eaves of the American Museum of Natural History.

Schieffelin never got around to introducing more of Shakespeare's birds to Central Park, but the sole species in his experiment thrived. His legacy has since spread beyond Manhattan and into every corner of the continent.

The 200 million descendants of those first 100 starlings are what Zichello and her students made the focus of their research. Over the 2016-2017 school year, the group met for two hours twice a week at the same museum where that first nest was discovered. A quick stroll around the building reveals that many of Schieffelin's birds didn't travel far. But those that ventured off the island eventually spawned populations as far north as Alaska and as far south as Mexico. By sampling genetic data from starlings collected around the United States, the researchers hoped to identify how birds from various regions differed from their parent population in New York, if they differed at all.

Four student researchers at the American Museum of Natural History
Valerie Tam, KaiXin Chen, Angela Lobel and Jade Thompson (pictured left to right)
(©AMNH/R. Mickens)

There are two main reasons that North American starlings are appealing study subjects. The first has to do with the founder effect. This occurs when a small group of individual specimens breaks off from the greater population, resulting in a loss of genetic diversity. Because the group of imported American starlings ballooned to such great numbers in a short amount of time, it would make sense for the genetic variation to remain low. That's what Zichello's team set out to investigate. "In my mind, it feels like a little accidental evolutionary experiment," she says.

The second reason is their impact as an invasive species. Like many animals thrown into environments where they don't belong, starlings have become a nuisance. They compete with native birds for resources, tear through farmers' crops, and spread disease through droppings. What's most concerning is the threat they pose to aircraft. In 1960, a plane flying from Boston sucked a thick flock of starlings called a murmuration into three of its four engines. The resulting crash killed 62 people and remains the deadliest bird-related plane accident to date.

Today airports cull starlings on the premises to avoid similar tragedies. Most of the birds are disposed of, but some specimens are sent to institutions like AMNH. Whenever a delivery of dead birds arrived, it was the students' responsibility to prep them for DNA analysis. "Some of them were injured, and some of their skulls were damaged," Valerie Tam, a senior at NEST+m High School in Manhattan, tells Mental Floss. "Some were shot, so we had to sew their insides back in."

Before enrolling in SRMP, most of the students' experiences with science were limited to their high school classrooms. At the museum they had the chance to see the subject's dirty side. "It's really different from what I learned from textbooks. Usually books only show you the theory and the conclusion, but this project made me experience going through the process," says Kai Chen, also a senior at NEST+m.

After analyzing data from specimens in the lab, an online database, and the research of previous SRMP students, the group's hypothesis was proven correct: Starlings in North America do lack the genetic diversity of their European cousins. With so little time to adapt to their new surroundings, the variation between two starlings living on opposite coasts could be less than that between the two birds that shared a nest at the Natural History Museum 130 years ago.

Students label samples in the lab.
Valerie Tam, Jade Thompson, KaiXin Chen and Angela Lobel (pictured left to right) label samples with Dr. Julia Zichello.
©AMNH/C. Chesek

Seeing how one species responds to bottlenecking and rapid expansion can provide important insight into species facing similar conditions. "There are other populations that are the same way, so I think this data can help [scientists],” Art and Design High School senior Jade Thompson says. But the students didn't need to think too broadly to understand why the animal was worth studying. "They do affect cities when they're searching for shelter," Academy of American Studies junior Angela Lobel says. “They can dig into buildings and damage them, so they're relevant to our actual homes as well.”

The four students presented their findings at the museum's student research colloquium—an annual event where participants across SRMP are invited to share their work from the year. Following their graduation from the program, the four young women will either be returning to high school or attending college for the first time.

Zichello, meanwhile, will continue where she left off with a new batch of students in the fall. Next season she hopes to expand her scope by analyzing older specimens in the museum's collections and obtaining bird DNA samples from England, the country the New York City starlings came from. Though the direction of the research may shift, she wants the subject to remain the same. "I really want [students] to experience the whole organism—something that's living around them, not just DNA from a species in a far-away place." she says. "I want to give them the picture that evolution is happening all around us, even in urban environments that they may not expect."

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Meet the Tully Monster, the Prehistoric Beast That Defies Categorization
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During the Carboniferous Period—a geologic period that lasted from about 359.2 to 299 million years ago, during the late Paleozoic Era—the world was filled with frightening, foreign, and funny-looking creatures. One of the most puzzling of these prehistoric animals may have been Tullimonstrum, better known as the Tully monster.

The Tully monster was a sea creature that resembled a giant worm crossed with a small squid. Out of its head jutted a long, skinny appendage with a hook that may have been a mouth, and its eyes were attached to fleshy stalks.

As bizarre as these features might appear to the modern eye, scientists in recent years have focused more on whether or not the Tully monster had a backbone. This defining feature could help them figure out the creature's evolutionary relationship to its ancestors and descendants. But so far, as PBS Eons explains below, experts are still at a loss for where the Tully monster fits into the tree of life.

Learn more about the mysterious Tully monster below:

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