As the Ancient Greeks used to say, "Know Thyself." It probably was meant a little more philosophically that we're choosing to interpret it, but learning about how your body is put together and why is some seriously fun stuff.
We've all marvelled at our fingers and toes, wrinkling into prunes in the bath. We've all stared at that weird fleshy appendage hanging down in the back of our throats.
We've all known someone - or been that someone - with an emergency appendectomy. "It's fine," they say, "the appendix is completely useless anyway."
But our bodies are amazing machines, and, while we may not need some of its features any more, there's very little in our anatomies with no purpose whatsoever.
And about those things we don't need any more? They're evidence of where we've been - and that we continue to evolve even to this day.
Your appendix
Turns out the human appendix - that weird structure attached to the colon that seemed to have little purpose but to occasionally inflame - isn't just an evolutionary vestige after all.
Recent research has found that it might play a key role in our immune systems by harbouring good bacteria that help fight infection. Good work, little buddy!
That extra ear hole
(Smooth_O/Wikimedia Commons)
If you look carefully at your ears, you might notice you have a tiny additional hole just where the helix meets the side of your head.
This is called the preauricular sinus, and only a tiny percentage of people have them. It's actually a rare birth defect first documented by Van Heusinger in 1864.
We don't know why we have them - but evolutionary biologist Neil Shubin of the University of Chicago and the Field Museum of Natural History has hypothesised that they're an evolutionary remnant of fish gills.
Wrinkly fingers
(Brenderous/Flickr/CC-BY-2.0)
If you spend too long in the swimming pool, you're going to notice that your fingers and toes start to look a little like raisins. This might not be pointless, according to a paper published in the journal Biology Letters in 2013.
They conducted experiments and found that underwater objects were manipulated much more adroitly by wrinkled fingers than unwrinkled fingers - suggesting that the feature exists to give us improved grip in both handling objects and walking when wet surfaces are involved.
Makes sense, doesn't it?
Junk DNA
We have a lot of DNA in our body that, until recently, didn't really seem to do anything.
It doesn't create proteins, and it seems to make us more susceptible to damage and disease - but it makes up a significant part of our genome. If it wasn't somehow beneficial, evolution would have at least started phasing out this so-called "junk DNA," but that hasn't happened.
Recently, researchers may have figured out what it's for - it plays a critical role in holding out genome together by ensuring that chromosomes bundle correctly inside the nuclei if our cells. Without that function, cells die - so it seems like "junk" DNA is not so junky after all.
"Useless" immune cells
We have these immune cells in our bodies that nobody could figure out what they were for.
It was a real head-scratcher, because these "silenced" lymphocytes are present in our bodies in large numbers and only seemed to emerge to attack the body in autoimmune diseases. It looks like a liability, right?
But it ain't. It turns out that the cells represent a new type of immunity that we didn't know about before - they attack dangerous infections that otherwise evade the immune system by disguising themselves as part of the body. A pretty useful line of defence to have, wouldn't you say?
Gut bacteria
There's a reason that experts have recently suggested that we all start referring to ourselves using the royal "we".
In recent years, research has found that the microbes that live inside of us, especially our intestines (our microbiome), are symbiotic - and they have far more of an effect on our lives than we realised.
They have been implicated in such illnesses as multiple sclerosis, Parkinson's disease, cancer and chronic fatigue syndrome, which means they may be pretty danged important. But they also seem to play a role in regulating other things, too - such as our appetites, and even our moods.
Interstitium
Turns out we may have an organ wrapped around our other organs, and it's been hiding in plain sight for all this time. The newly classified organ is called the interstitium, and previously scientists had just thought it was relatively unremarkable, relatively solid tissue to fill the space between our organs.
It's actually filled with fluid, supported by a collagen lattice, and it helps protect our organs from external shocks as we move around, much like air cushions in running shoes.
The pink bit in your eye
(Peter Clarke/Wikimedia Commons/CC-BY-SA-4.0)
If you look in the mirror, you'll see a little pink bit of conjunctival tissue in the corner of your eye. This is called the plica semilunaris, and these days its primary function is to help with tear drainage and eyeball mobility.
But once upon a time it was a nictitating membrane - what we call a third eyelid, a translucent eyelid that can be drawn over the eye to keep it moist and protected while maintaining a measure of vision.
If you have a cat or a dog, you may have seen their third eyelid while they're sleeping. Humans and most other primates don't need this feature any more, so it evolved away a long time ago - but we still have that vestigial lump of tissue.
Last year, doctors reported the second known case of a nictitating membrane in a human. A nine-year-old girl had a persistent membrane across her left eye that could not be retracted. It was surgically excised, and her eye underneath was fine.
A version of this article was first published in June 2018.