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Thursday, March 28, 2024

Your body is a museum of natural history

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HISTORY is not just about past events. History is about the threads that connect the events of the past to the realities of today. Thus, the claim that past events can only be understood by those who have lived through them is as absurd as it is demonstrably false.

Consider your body. Although it exists in the present, it is nonetheless intimately connected to all the bodies of your ancestors that came before it. Their histories leave traces in your skin, in your bones, in the blood that runs through your veins. Your body is a museum of natural history curated by natural selection. 

Let’s look at one exhibit in this museum. Rest your arm on a flat surface, palm up. Now press your pinky against your thumb. Some of you will see a raised strip that runs through your wrist. That raised strip is a tendon connected to a muscle called the palmaris longus. It is a muscle we don’t need anymore, which is why many people, like myself, are missing it. While it is a muscle used for gripping, studies have shown that people who lack it don’t have less grip strength. In fact, the tendon connected to the palmaris longus is one of the first surgeons chose to remove to replace other tendons in the body of a patient.

Why do most of us have the palmaris longus then? Well, because our ancestors had it. They had it because they climbed trees and used their forelimbs to move around. Among primates today, the ones that climb the most are the ones with the most developed palmaris longus. For example, in lemurs and monkeys this muscle is thick and long. Meanwhile, it is less developed among chimps, gorillas, and humans.

We don’t climb much anymore, but the climbing habits of our ancestors leave more than just traces in our bodies. The palmaris longus is an example of a vestigial organ. It is a vestige, or better yet a legacy, of the past.

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Here’s another exhibit in that museum, another vestigial organ. Connected to your earlobes are three muscles. Many other animals, like dogs and cats, have these same muscles. In dogs and cats, these muscles move the earlobes to face the source of a sound. In humans, the same muscles try to do the same, but of course they fail. Some people can move their ears more than others, but never to the degree that many other mammals can. We don’t use these muscles anymore. To make our ears face the source of sound, we move our heads using our necks. But our ancestors had and used these muscles, and so we still have them.

It’s not just the useless parts of our bodies that show our connections to the past. Just look at your arms and feet. Your arms and feet reveal your inner fish. (Take that, Ariel!)

Feet and arms are not the only ways to move on land. You can move using pseudopods like snails. You can slither through the ground like a snake. You can lift yourself off the ground using wings. And feet and arms don’t have be to constructed in the way our feet and arms are constructed, with bones on the inside and bits of flesh attached outside. The legs of insects have bones on the outside and flesh in the inside.

Our feet and arms are the way they are because we got them from our fish ancestors. We don’t share those same ancestors with snails, which is why snails don’t have legs. We don’t share those same ancestors with insects, which is why their legs are different from ours. We share those ancestors with snakes, which is why snakes actually have vestigial legs, with bones to match, tucked inside their bodies. We share those fishy ancestors with birds, which is why the wings of birds are constructed like our arms, down to every last bone (except the bones have different shapes, hence arms versus wings).

In fact, every bit of your body is an exhibit in this museum of natural history: your eyes with their blind spots, the bones in your middle ear that came from the bones in the jaws of our fishy ancestors, and so many more.

The museum that is our body is not just a reminder of the past; it is a living legacy of that past. In the same token, there is no running away from any kind of history, no “moving on.” There is only learning from it in order to move forward. In this act of moving forward, the threads that connect us to the past never get severed, they only get stretched. Misunderstanding or underestimating them can only hold us back. We ignore these threads at our peril. 

Pecier Decierdo is resident physicist and astronomer of The Mind Museum.

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