Your body’s full of stuff you no longer need. Here's a list.

Evolution doesn't clean up after itself very well.

Your body’s full of stuff you no longer need. Here's a list.
Image source: Decade3d-anatomy online via Shutterstock
  • An evolutionary biologist got people swapping ideas about our lingering vestigia.
  • Basically, this is the stuff that served some evolutionary purpose at some point, but now is kind of, well, extra.
  • Here are the six traits that inaugurated the fun.

Evolutionary anthropologist and Boston College post-doc, Dorsa Amir, started the whole thing with a series of eight tweets, and boy did she start something fun. Amir laid out a list of weird, once-useful details of the human anatomy that we continue to carry around within — and on — us. Basically, this is the stuff that served some evolutionary purpose at some point, but now is kind of, well, extra.


Natural selection, after all, has no reason to clear away unnecessary traits if they pose no evolutionary disadvantage. And when we say "started the whole thing," what we mean is that, this being Twitter, some arguing was inevitable. Some people took issue with Amir's use of the word "vestigial." One issue with the word is that early traits may still be beneficial in ways we don't yet know — the microbiome-managing appendix and the immune system's tonsils were both considered among these for some time. A trait's stated assumed value is also always just our best guess, so a certain amount of uncertainty is understood to be baked-in. It's important to remember, too, that if a mutation just happened to happen and persisted because it was useful, it's not the same thing as saying it has a reason to exist. The reason was randomness, unless one doesn't believe in evolution.

Which gets us to the second type of argument Amir's posts generated. Some creationist-intelligent design believers seem to be patrolling Twitter to shout down references to science where it arises. Probably this post will also get them going. Amir has nonetheless started a list and a conversation that is totally worth checking out, hair-splitting aside. Here are the six traits that inaugurated the fun.

The plica semilunaris

The human eye in alarming detail. Image source: Henry Gray / Wikimedia commons

At the inner corner of our eyes, closest to the nasal ridge, is that little pink thing, which is probably what most of us call it, called the caruncula. Next to it is the plica semilunairs, and it's what's left of a third eyelid that used to — ready for this? — blink horizontally. It's supposed to have offered protection for our eyes, and some birds, reptiles, and fish have such a thing.

Palmaris longus

Palmaris longus muscle. Image source: Wikimedia commons

We don't have much need these days, at least most of us, to navigate from tree branch to tree branch. Still, about 86 percent of us still have the wrist muscle that used to help us do it. To see if you have it, place the back of you hand on a flat surface and touch your thumb to your pinkie. If you have a muscle that becomes visible in your wrist, that's the palmaris longus. If you don't, consider yourself more evolved (just joking).

Darwin's tubercle

Darwin's tubercle. Image source: Wikimedia commons

Yes, maybe the shell of you ear does feel like a dried apricot. Maybe not. But there's a ridge in that swirly structure that's a muscle which allowed us, at one point, to move our ears in the direction of interesting sounds. These days, we just turn our heads, but there it is.

Goosebumps

Goosebumps. Photo credit: Tyler Olson via Shutterstock

It's not entirely clear what purpose made goosebumps worth retaining evolutionarily, but there are two circumstances in which they appear: fear and cold. For fear, they may have been a way of making body hair stand up so we'd appear larger to predators, much the way a cat's tail puffs up — numerous creatures exaggerate their size when threatened. In the cold, they may have trapped additional heat for warmth.

Tailbone

Coccyx.

Image source: Decade3d-anatomy online via Shutterstock

Way back, we had tails that probably helped us balance upright, and was useful moving through trees. We still have the stump of one when we're embryos, from 4–6 weeks, and then the body mostly dissolves it during Weeks 6–8. What's left is the coccyx.

The palmar grasp reflex

Palmar reflex activated! Photo credit: Raul Luna on Flickr

You've probably seen how non-human primate babies grab onto their parents' hands to be carried around. We used to do this, too. So still, if you touch your finger to a baby's palm, or if you touch the sole of their foot, the palmar grasp reflex will cause the hand or foot to try and close around your finger.

Other people's suggestions

Amir's followers dove right in, offering both cool and questionable additions to her list.

Fangs?

Hiccups

Hypnic jerk as you fall asleep

This thing, often called the "alpha jerk" as you drop into alpha sleep, is properly called the hypnic jerk,. It may actually be a carryover from our arboreal days. The hypothesis is that you suddenly jerk awake to avoid falling out of your tree.

Nails screeching on a blackboard response?

Ear hair

Nervous laughter

Um, yipes.

Twitter should always be so much fun.

A historian identifies the worst year in human history

A Harvard professor's study discovers the worst year to be alive.

The Triumph of Death. 1562.

Credit: Pieter Bruegel the Elder. (Museo del Prado).
Politics & Current Affairs
  • Harvard professor Michael McCormick argues the worst year to be alive was 536 AD.
  • The year was terrible due to cataclysmic eruptions that blocked out the sun and the spread of the plague.
  • 536 ushered in the coldest decade in thousands of years and started a century of economic devastation.
Keep reading Show less

Google invents a new tool that can make you hear color

A machine learning system lets visitors at a Kandinsky exhibition hear the artwork.

Culture & Religion

Have you ever heard colors?

Keep reading Show less

Study: You would spend 90 extra days in jail in a private prison

A new study suggests that private prisons hold prisoners for a longer period of time, wasting the cost savings that private prisons are supposed to provide over public ones.

Politics & Current Affairs
  • Private prisons in Mississippi tend to hold prisoners 90 days longer than public ones.
  • The extra days eat up half of the expected cost savings of a private prison.
  • The study leaves several open questions, such as what affect these extra days have on recidivism rates.
Keep reading Show less
Quantcast