The human body is a wondrous and gross thing and the grossness changes over time even as the wonder dims and sags but here are so super weird and absolute facts about it that you probably didn’t know or definitely need to be reminded of.

Let’s Start With Baby Humans

1. You absolutely, 100% used to have a tail

In fact you used to look like a tadpole but as you grew out of that you developed a weird little tail, what’s called a vestigal tail because it’s a vestige of a previous evolutionary period.

You see, your body is made up on DNA that’s mutated over hundreds of millions of years and it still contains older stuff (way older as you’ll see in a bit). One of those older things is a tail. Now usually what happens is that in utero your body eventually rejects the tail and it just sort of dissolves. But sometimes, not often, it doesn’t get rejected and you end up with a baby with an awful looking tail, like so.

Yes, that’s a baby butt with weird finger looking tail thing growing above it. These tails are never functional and this is actually one of the better looking ones I could find. They’re almost all shriveled and gross which is why they’re cut off almost immediately and it’s never spoken of again.

2. You Used To Have Gills Too

Okay, they’re not exactly gills, not anymore. Like I said, you and I, all of us were very tadpole-like as fetuses and these “gill slits” make that seem less like coincidence than it might otherwise. While you and I didn’t have functioning gills in utero we did all have lines on our necks that look exactly like gills. In fact, they look so much like gills that scientists believe it’s a remnant of our super ancient ancestors, fish.

Fish, birds, reptiles, they all have these and they have a specific name. In fish, these become gills and some other things, in humans they become human things (like your jaw for instance) but the fact remains that at a certain state of development humans look they’re developing gills.

You can see a bunch of weird pictures of it here.

3. The Real Reason Why Human Babies Are So Lame

Human babies are helpless. They can do three things, eat, cry, and sleep and it they’re stuck this way for a long time. While chimp babies are running around getting in trouble and antelope babies are able to walk just minutes after being born, human babies can’t do anything. Why?

Well, it’s because our brains are enormous and, in utero, require tons of calories. What’s more, in order for a human woman to give birth to a baby that could learn to walk pretty quickly, she’d have to carry the thing for up to 21 months. That’s nearly two years. At nine months, a baby is already beginning to tax a woman’s ability to metabolize (digest and turn into energy) enough food for both her and the baby. In short, she’s burning out.

There’s no way a woman could live with a baby developing inside her for 21 months. She’d die. So, instead, nature found a compromise and you’re born at nine months and spend the next year and a half being carried around.

Then There’s Awkward And Oily Puberty Humans

4. Your Skin Kills Germs

To be fair, this is the case all the time but it’s particularly the case during puberty when we’re all at our oiliest and most disgusting.

So, your body is constantly producing oils and covering your skin with it. While this is a protection from heat and cold and stuff like it also does another thing, it makes your skin, all of it, slightly acidic. That’s right, the whole outside of your body is slightly acidic. Why? It’s part of your body’s immune response. A lot of harmful bacteria can’t bear even a slightly acidic environment. Add the salt from sweat into the mix and you have a pretty potent barrier against bacteria.

So, at least it was doing something besides making you look awful.

5. Adolescents Are Malformed Freaks (Basically Like Slender Man)

This is true and it’s all down to growth spurts. While everyone probably remembers their feet or ears seeming to be too big once puberty struck it’s actually your entire body.

Teenagers don’t grow uniformly, they grow in stages but there is an order to it. All the extremities grow first so your hands, feet, head, legs, and arms. Your torso and shoulders are the last to start growing which is teenagers are gangly and awkward before finally turning into beautiful swans and migrating off to college to learn how to go into debt.

6. Sexual Maturity Is Weird

Boys and girls don’t reach sexual maturity at the same time, at all, and it’s a bit strange. Pretty much the first thing that matures in boys is the genitals. It’s basically immediate. Puberty starts and boys’ genitals immediately get bigger and they’re able to produce sperm very early in puberty way before anything else develops like muscles or extra hair or brains or anything.

Girls are exactly the opposite. Literally everything else about a girl develops before her ability to reproduce, probably because it’s so complicated. Even after a girl has her first period she’s still not considered sexually (reproductively) mature until a couple of years afterward. By then, the boys aren’t just sexually mature, they’re reaching their peak fertility years of 17-19.

Grown Adult, Getting Fatter Humans

7. Grown Ups Are Actually Brand New

Once you’re past that awkward puberty stage there is literally no cell in your body that has not been replaced. Of course, cells are being replaced constantly when they’re damaged but even healthy cells age and have to be shed and new ones replace them. Your heart, your lungs, your lips and eyes, everything has been replaced.

Only one problem, the brand new copies aren’t as the cells they replaced. Hello wrinkles!

8. You Now Have To Make A Choice

There are two kinds of aging. The first is called primary aging and has to do with genetics and the natural process of getting older. The second is called, appropriately, secondary aging and has to do with how you treat your body. If you smoke, drink a lot, don’t exercise, eat bad food, your body will age more quickly than it would have without those things. Hormones and puberty are no longer making sure you’re basically invincible.

Your metabolism starts to slow down because you’re no longer developing a whole new body type and it becomes much easier to gain weight if you’re sedentary whereas before you could most likely do nothing all day and live solely on a diet of candy bars, McDonalds, and Coca Cola and your body would just turn that into new bones, muscles, and sex organs.

9. The Crash Years

Despite your metabolism slowing down, you’re still doing well for the most part in your 20s and 30s if you take care of yourself and don’t do too many things that cause secondary aging. But there are limits to that. Once you hit 40, that’s when primary aging starts to take off. In fact the years between 40 and 65 are when everything starts to go to crap.

These  are the years when all the things you care about start diving towards destiny. Your vision gets worse, your genitals get worse or your reproductive organs start getting old. For women, as you likely know, this is the period when you stop having your period.

But, what you may not know is that Menopause (should be called Menostop) usually takes a few years however it can happen in as little as six months. What you get along with that is increased anxiety, a worse memory, increased irritability, and mood swings. It’s basically your teens all over again.

For men, these are the Viagra years. Those years end when you die.

Old And Older Humans Of Quiet Dignity

10. Congratulations, You’re Old

Getting old isn’t for the faint of heart. — Some old person, probably

While a friend of mine once hypothesized that if you could live to 125 you’d experience a second puberty and live a second life, that’s not what actually happens.

See, by 65 you’re really starting to fall apart but it’s not as bad as you think. While there’s an idea out there that every old person gets shuttled off to a retirement home it’s not close to being true. Only 3.6% of The Olds get sent to a place like that. Most live at home or with family.

11. Women Get Their Revenge

By 75, men start dying in droves such that women, who’ve paid the physical price for having a womb, outnumber men 100 to 76. By the age of 85, half of all the men are dead and there’s only 49 men for every 100 women. So, ladies, if you’re looking forward to a few years of quiet time before you die, you’re absolutely going to get it.

12. This Revenge Is Bittersweet

The older you are, the more likely you are to be poor. Old people have the highest poverty rates in the nation by demographic at 10.5% and, if you’re Black or Hispanic, that rate is tripled.

And here’s the sneaky thing about that retirement home statistic, retirement homes are generally for people with money because they’re expensive. Most old people, as I said, live alone at home until they die. So, that pop culture trope that all old people end up in retirement homes is actually just true for people who have money.

What’s more, whether you’re a woman or a man, chances are that by 85 everyone you know is already dead. So, you’re probably poor because your retirement money has long run out, your spouse may or may not be dead, and almost all your friends are dead.

Be good to your children!