Pregnancy is a hardcore sci-fi epic of war, peace and compromise.
Babies are basically very cute tumours that grow a completely new organ inside a different human.
Their mom's body graciously allows this, while the new life saps her resources and challenges her immune system to its limits for months,
Biology is brutal and beautiful and metal.
Let's zoom in and observe this brutal struggle for survival that, in the best case, ends in one of the most magical things a new life.
Our story begins with an army of tens of millions of sperm cells that immediately face death.
They're on a tight timer before they run out of energy and die, but this is the least of their problems right now.
Like all bodily openings, the female reproductive tract is a fortress defending against invaders.
The future.
Mum's body has set up deadly barriers and puts the sperm through a brutal process that kills almost all of them and ideally selects the strongest and fittest one.
The first deadly obstacle is a highly acidic environment, guarded by hundreds of thousands of guard cells.
The acidity kills millions, especially of the weaker sperm, within the first half hour, although they have a bit of protection.
Seminal fluid is alkaline, so it makes this first obstacle a little less deadly.
The survivors reach the next obstacle a treacherous maze full of protein nets where millions more find a brutal end, getting stuck and lost.
Now, if a woman is in the part of her menstrual cycle where she's ovulating, her body helps the sperm out a bit by releasing chemicals that guide the way and by being a bit less hostile.
Luckily for our brave sperm, this is the case today.
Only a couple of hundred less than 00001 of the original sperm pass through into the uterine cavity, where two tunnels branch out.
Here, mucus helps transport the stronger sperm to move on while weeding out the weaker ones.
The mums' immune cells pick off and devour every cell that trails behind or takes the wrong turn.
And then, finally, maybe just a few dozen sperm reach their goal, the mighty giant egg.
10000 times bigger than them.
It's an industrial-scale monster loaded with nutrients and nearly 100000 mitochondria the powerhouse of the cell, 50 times more than an average cell.
But the egg is not easily conquered.
The survivors get closer and try to get in until the egg decides to accept a single one of them.
The genes of two individuals merge.
The egg stops being part of its mother.
It's something else now.
A new being with its own agenda.
Not a human yet, but the potential to become one.
Like a thought that's not yet a word.
But its mum's body hasn't decided yet if she wants to say it out loud.
It will have to fight for that.
For a few days, it rapidly divides and grows to a couple of hundred cells, while traveling down to the uterus, the part of the female reproductive system, where it will try to make its new home.
Here, it begins to divide into two specialized teams of cells.
One will eventually become the baby.
The other cells are trophoblasts and their job is to turn into a temporary organ inside the mother, the placenta, that will make pregnancy possible and eventually die.
This means that when you were an embryo there was this whole other part of you, not like a twin, even closer maybe like a guardian angel clone.
These cells never had the chance to become a human.
Their only purpose in life was to make you exist.
In any case, the following days are the most dangerous for the potential new life.
Like a tennis ball rolling through syrup, the young embryo moves along the uterus and tries to take a hold.
An intense chemical dialogue between two living things begins.
The embryo releases dozens of chemicals that announce its presence and asks the guard cells of the uterine wall to allow it to please please please, attach itself so it can survive.
The uterus responds with dozens of hormones and immune signals itself.
If it's satisfied with the quality of the chemical conversation, its cells allow it.
If it doesn't, the embryo will be lost and die.
This is where we begin to see the interests of both living beings no longer completely align anymore.
Pregnancy is a huge energy investment, so the mother's body will eject the embryo if it doesn't see it as viable.
The embryo, on the other hand, faces a life and death situation and tries to stay alive at any price.
So it's not asking politely, but deploying thousands of infiltration units, bubbles filled with genetic material, kind of like a human virus.
They sort of invade the uterine cells and try to brainwash them, so they help it attach itself rather than rejecting it.
During this time, one of the weirdest features of pregnancy occurs.
The uterus provides uterine milk.
Not real milk, but a clear fluid filled with nutrients and hormones that the young embryo sucks up hungrily to gain additional energy until it gets inside.
If the embryo is allowed in, the implantation was successful, the first critical hurdle.
The next step is to reach the blood vessels of its mother, the only way to survive if it doesn't want to starve.
The trophoblasts begin to clone themselves on a massive scale and turn into different specialists.
One of them turns into a violent invader that starts drilling into the uterine tissue like a tiny parasitic octopus with many arms spreading and growing.
This is a brutal process, ordering loads of its mum's uterus cells to destroy themselves, killing others directly or even devouring some cells whole.
While this sounds brutal, and it is, this process is highly regulated and doesn't hurt the mum.
It's another test.
The mum's body monitors carefully how the embryo is doing.
Is it growing quickly or is it more chill?
If an embryo has genetic damage or chromosomal abnormalities, it will spend way more energy on repairing itself and maybe grow more erratically.
This makes it metabolically noisy, releasing loads of chemicals the mum's immune cells pick up, which provokes them and makes it more likely that they'll destroy it.
On the other hand, if the embryo is weak, it's metabolically too quiet and the mum will stop talking to it, which also ends the pregnancy.
This embryo is just right.
So the mum's cells release a flood of different chemicals to help it out, support it growing and, most importantly, activate her immune system.
Usually this would be very bad.
The immune system kills everything that's not part of the mum's body, and this embryo is clearly not part of her.
But the immune cells of the uterus surround the embryo and start helping it, guiding the trophoblast to grow further.
They create a physical and chemical safe zone that tells dangerous immune cells, like T cells, to stay away.
The embryo has its own motives and doesn't want to rely on its mother's goodwill alone, so defensive trophoblasts send out signals that kill her immune cells if they get too close and could start attacking it.
Hundreds of cells go even further and leave the embryo behind.
They spread all across the mum's body, entering organs, even the brain.
We don't know what all of these cells are doing, but we think that they're probably telling her immune system that the embryo is not to be attacked, that it should be left alone or even protected.
These cells may stay inside the mother for years or even decades.
It's likely that parts of you are still in your mother.
Around eight weeks after the egg was fertilized, the transition from the embryo to fetus begins.
The size of an olive.
Its organs begin to form and it turns from a blob into something vaguely human-like.
Is there a clear point where a clump of cells becomes a human?
Not really.
It's a fluid transition and every society and person, be it morally or legally, marks this moment differently.
Meanwhile, construction trophoblasts are busy building a spongy finger-like structure that expands further into the uterus a completely new organ.
The placenta, an organ that you once grew inside your mother, that was ejected after your birth and died a silent death while everybody was busy welcoming you into the world.
In our story, the placenta is now the new home of the fetus.
An enormous fortress protecting it from microbes that could infect and kill it in its still pretty fragile state.
It even has its own mini immune system placental immune cells that gobble up anything that poses a threat.
Other placental cells creep along the inside of the mum's blood vessels, stretching them and connecting the fetus through the umbilical cord on the other side.
With the blood flow secured, it's time to load it with as much food as possible.
The placenta releases hormones that funnel glucose directly to the fetus, stealing energy from its mum.
If the fetus goes too far and asks too much, this can sometimes lead to gestational diabetes for the mum during the pregnancy, starving her body of energy.
The mother's body is trying to support the new life, but not at the cost of her own survival.
In a sense, the mother's genes inside the fetus still have a stronger allegiance to her than to the new being.
But its father's genes don't.
They want the fetus to survive at all costs.
So while there's a sort of fragile peace between both parties, it is just that.
Their interests are not perfectly aligned, and both sides have to deal with that.
In the next few months, the fetus will increase its weight over a billion times, which demands a staggering amount of energy and cooperation.
They still need to work together to get out of this alive.
But if the fetus gets to this point in the pregnancy, chances are pretty high that it will become a baby, like you once were.
A proper human, like you are today.
A being with immense potential.
If you're alive today, then you went through an amazingly brutal selection process.
From a little pack of genes traveling through an incredibly deadly obstacle course, fighting for your survival with desperate words spoken through chemicals and sneaky actions, trying to outsmart the system, fighting to be alive in this world.
But this is only one side of the story.
You were also chosen by hormones that led you to the right place, by the egg allowing you to merge into one.
By your mum's body that liked how you spoke to her, by her cells that protected and cared for you.
Nourished by an incredible amount of energy that your mother gifted you.
Our biology is a brutal, unforgiving, but necessary part of the greatest wonder there is.
The creation of new life.
Of you.
Of all of us.
Kids fill us with a sense of wonder.
It's our job to foster this sense of wonder in them as well.
Our sponsor KiwiCo, is a great start to spark curiosity in your kids from the earliest moments on, basically from birth.
This is one of their crates for newborns, so let's explore it together.
There's a tummy time pillow, some black and white cards, a sensory mat, and a mirror.
It's the Let's Bond Panda Crate, a kit that helps your newborn explore its brand new sensations of vision, hearing and motor control.
At the same time, you get to know this tiny new human in your life and learn about how it currently experiences the world.
This crate is part of the KiwiCo Panda Crate line of research-backed toys and activities to support your baby's development.
You can promote vision, hearing and gross motor skills in the first months of a baby's life, or rhythm and language skills later.
Whatever stage of life, KiwiCo has the curriculum to promote a kit's development at every step.
All their toys are created and backed by experts and made from high-quality materials.
A KiwiCo subscription could be the gift that keeps on giving for your own kit, a baby shower or any niece nephew, godchild or other little one in your life, with a new box of wonders arriving every month.
We like KiwiCo because they're fostering a mindset of making learning an ongoing exploration, just like we try to do with our videos.
If you want to try out KiwiCo, click on the link in the description or use the code Kurzgesagt to get 50 off your first monthly KiwiCo crate.
Here is your special connection to Kurzgesagt.
If you're craving more between videos, our newsletter delivers the latest updates straight from the burp's nest to your inbox.
You'll be the first to access limited releases and deals.
Learn about new product drops before the rest and get fascinating snackable science facts about our favorite topics.
Of course, we'll also let you know about new video releases and updates from our game department.
Plus, you'll get exclusive freebies like this cosmic diorama.
Subscribe now to stay connected.
And don't miss the very special product drop coming soon.
