Over the course of our lives, we see our bodies transform as part of natural human development. Our arms, legs, and other bits and pieces may change shape due to new activities, dietary adjustments, or even a surgical procedure. We notice the shift and may - or may not - like what we see. What we don't realize, however, is that evolutionary changes to the human form are continuing to happen.
Signs of evolution in the human body exist from head to toe. They differ by individual, are influenced by one's circumstances and surroundings, and perpetuate questions about the effects of nature and nurture on the physical form. The study of human anatomy continues to incorporate how evolution is transforming our bodies, and it tries to better explain how evolution has very literally shaped us over the centuries. Here are some mind-blowing facts about how our bodies have transformed, and are still doing so.
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The Human Jaw Is Shrinking - And Has Been For Centuries
When a 2015 scientific study announced that humans once had "an almost 'perfect harmony' between their lower jaws and teeth," the assertion echoed what scholars had been saying for years - the human jaw is shrinking.
In 2011, a study of more than 300 skulls indicated that, as humans became more sedentary, the resulting change in diet - from hunting and gathering to pastoral farming and processed food - caused a decrease in the amount of force required to chew. Over time, the jaw took on a new shape, which has become increasingly problematic for modern humans.
Due to jaw shrinkage, more and more people experience cramped teeth and, in turn, need orthodontic work. Sleep apnea and comparable sleep disturbances are also traced to the change in jaw shape.
One consequence of shrinking jaws is the absence of wisdom teeth. As of late 2020, research indicated more humans were being born without wisdom teeth than ever before. Called a "microevolution," the lack of wisdom teeth has been attributed to "our faces getting a lot shorter... [with] not as much room because of smaller jaws."
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There's A Network Of Fluid In Your Body No One Identified Until 2018
Unofficially considered an organ, the interstitium was first identified in 2018. As a network of open, fluid-filled spaces, the interstitium replaced what researchers had previously thought was a "wall" of collagen.
The interstitium is found throughout the human body, including in tissues under the skin, in the digestive and respiratory systems, and around the muscles. According to the initial study, interstitium protects the body and produces lymph, the fluid that's essential to immune cell function.
While the interstitium may be new to most humans, there are indications physicians and scientists knew about it for centuries prior to its "discovery." What is new, however, is the composition of the interstitium and the possible role it has in the spread of disease.
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Forearms May Be Missing Muscles, But They're Gaining Arteries
There's a muscle in the human forearm called the palmaris longus. While it has no apparent function for modern humans, scholars believe it remains important for primates that "perform most daily activities in threes or use forelimbs for ambulation."
There's a noticeable absence of the palmaris longus in about 14% of humans, albeit one that varies significantly by location. In 2015, researchers found its absence across the world ranges between 1.5% and 63.9%, with the highest numbers present in Egypt and Turkey.
As the muscle's absence continues to be studied, another part of forearm anatomy is changing as well. An increasing number of humans are reaching adulthood with their median arteries, which run through the forearm and hand of fetuses in the womb but, in the past, vanished as the arm developed. According to a 2020 study, however:
The prevalence [of the median artery] was around 10% in people born in the mid-1880s compared to 30% in those born in the late 20th century, so that’s a significant increase in a fairly short period of time, when it comes to evolution.
Due to the speed of the change, researchers project "a majority of people will have a median artery of the forearm by 2100." Once 50% of the population presents with a median artery, "it should not be considered as a variant, but as a 'normal' human structure."
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A Knee Bone Almost Disappeared - But It's Making A Comeback
Medical records from 1875 indicate nearly 18% of patients had a small bone in their knee called the fabella (literally "little bean" in Latin). By 1918, that percentage decreased to nearly 11%. One century later, however, as many as 39% of patients have a fabella - but that's not necessarily a good thing.
According to researchers at Imperial College London, the bean-like bone "just causes us problems." As a small sesamoid bone located within tendons, the fabella is present in many individuals with arthritis and inflammation in their knees.
The exact function of the bone isn't clear because, in the words of Dr. Michael Berthaume, "nobody has ever looked into it." He continued:
The fabella may behave like other sesamoid bones to help reduce friction within tendons, redirecting muscle forces, or, as in the case of the kneecap, increase the mechanical force of that muscle. Or it could be doing nothing at all.
The reason the bone is becoming more prevalent, as theorized by Berthaume, involves the larger composition of the human body. With taller and heavier humans, added knee pressure "could explain why fabellae are more common now than they once were."
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Researchers (May Have) Found A New Layer In The Human Eye In 2013
Dua's layer, named for the head of a research group from the University of Nottingham, was discovered in 2013. What Harminder Singh Dua and his fellow researchers found was a previously undetected (and 6th) layer of the cornea that measures roughly 15 micrometers.
Research into Dua's layer continues; it's not clear if this is a "new" layer or one that was present all along but without clear identification. Another possibility, according to Dr. Loretta Szczotka-Flynn, is that Dua's layer "may be an artifact occurring in older corneas."
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Human Feet Creep Up In Size Each Year
Once humans hit adulthood, our feet stop growing as part of the development process. As we age, however, they continue to get bigger. Over time, pressure from walking, weakening of tendons and ligaments, and other activities make our feet expand and take on new shapes.
That's one phenomenon of human feet, but another developing trend is an overall increase in size. In 2012, a report from the National Shoe Retailers Association indicated women's feet grew more than a whole size during the previous 30 years. Men also saw increases and, two years later, evidence from the UK found women's feet were growing at comparable rates.
It's not clear why the human foot seems to be getting larger, but it may be related to the increased weight and height experienced by humans, too.