population of the New World dropped by at least 90%.

The cause?

Not the conquistadors and company -- they killed lots of people but their death count is nothing

compared to what they brought with them: small pox, typhus, tuberculosis, influenza, bubonic

plague, cholera, mumps, measles and more leapt from those first explorers to the costal tribes,

then onward the microscopic invaders spread through a hemisphere of people with no defenses

against them. Tens of millions died.

These germs decided the fate of these battles long before the fighting started.

Now ask yourself: why didn't the Europeans get sick?

If New-Worlders were vulnerable to old-world diseases, then surely Old-Worlders would be

vulnerable to New World diseases.

Yet, there was no Americapox spreading eastward infecting Europe and cutting the population

from 90 million to 9. Had Americapox existed it would have rather dampened European ability

for transatlantic expansion.

To answer why this didn't happen: we need first to distinguish regular diseases -- like

the common cold -- from what we'll call plagues.

1. Spread quickly between people.

Sneezes spread plagues faster than handshakes which are faster than closeness. Plagues

use more of this than this.

2. They kill you quickly or you become immune.

Catch a plague and you're dead within seven to thirty days; survive and you'll never get

it again. Your body has learned to fight it. You might still carry it -- the plague lives

in you, you can still spread it -- but it can't hurt you.

The surface answer to this question isn't that Europeans had better immune systems to

fight off New World plagues -- it's that the New World didn't have plagues for them to catch.

They had regular diseases but there was no Americapox to carry.

These are history's biggest killers, and they all come from the Old World.

But why?

Let's dig deeper, and talk cholera: a plague that spreads if your civilization does a bad

job of separating drinking water from pooping water. London was terrible at this, making

it the cholera capital of the world. Cholera can rip through dense neighborhoods, killing

swaths of the population before moving onward. But that's the key: it has to move on.

In a small, isolated group, a plague like cholera cannot survive -- it kills all available

victims, leaving only the immune and then theres nowhere to go -- it's a fire that burns

through its fuel.

But a city -- shining city on the hill -- to which rural migrants flock, where hundreds

of babies are born a day: this is sanctuary for the fire of plague; fresh kindling comes

to it. The plague flares and smolders and flares and smolders again -- impossible to

extinguish.

Historically, in city borders, plagues killed faster than people could breed. Cities grew

because more people moved to them than died inside of them. Cities only started growing

from their own population in the 1900s when medicine finally left its leaches and bloodletting

phase and entered its soap and soup phase, giving humans some tools to slow death.

But before that a city was an unintentional playground for plagues and a grim machine to

sort the immune from the rest.

So the deeper answer is that the New World didn't have plagues because the New World

didn't have big, dense, terribly sanitized deeply interconnected cities for plagues to

thrive.

OK, but The New World wasn't completely barren of cities, and tribes weren't completely isolated.

Otherwise the newly-arrived smallpox in the 1400s couldn't have spread.

Cities are only part of the puzzle: they're required for plagues, but cities don't make

the germs that start the plagues -- those germs come from the missing piece.

Now, most germs don't want to kill you, for the same reason you don't want to burn down

your house; germs live in you. Chronic diseases like leprosy are terrible because they're

very good at living in you and not killing you.

Plague lethality is an accident, a misunderstanding, because the germs that cause them don't know

they're in humans; they think they're in this.

Plagues come from animals.

Whooping cough comes from pigs, as does flu, as well as from birds. Our friend the cow

alone is responsible for measles, tuberculosis, and smallpox.

For the cow these diseases are no big deal -- like colds for us. But when cow germs get

in humans, the things they do to make a cow a little sick to spread make humans very sick.

Deadly sick.

Now, germs jumping species like this is extraordinarily rare. That's why generations of humans can

spend time around animals just fine. Being the patient zero of a new animal-to-human

plague is winning a terrible lottery.

But a colonial-age city raises the odds: there used to be animals everywhere; horses, herds

of livestock in the streets, open slaughterhouses, meat markets pre-refrigeration, and rivers

of human and animal excrement running through it all.

A more perfect environment for diseases to jump species could hardly be imagined.

So the deeper answer is that plagues come from animals, but so rarely that you have to raise

the odds with many chances for infection and even then the new-born plague needs a fertile environment

to grow. The Old World had the necessary pieces in abundance.

But why was a city like London filled with sheep and pigs and cows and Tenochtitlan wasn't?

This brings us to the final level, for this video anyway.

Some animals can be put to human use -- this is what domestication means: animals you can

breed, not just hunt.

Forget for a the moment the modern world: go back to 10,000BC when tribes of humans reached

just about everywhere. If you were in one of these tribes, what local animals could you

capture, alive, and successfully pen to breed?

Maybe you're in North Dakota and thinking about catching a Buffalo: an unpredictable,

violent tank on hooves, that can outrun you across the planes, leap over your head and

travels in herds thousands strong.

Oh, and you have no horses to help you -- because there are no horses on the continent. Horses

live here -- and won't be brought over until too late.

It's just you, a couple buddies, and stone-based tools. American Indians didn't fail to domesticate

buffalo because they couldn't figure it out. They failed because it's a buffalo. No one

could do it -- buffalo would have been amazing creatures to put to human work back in BC,

but it's not going to happen -- humans have only barely domesticated buffalo with all

our modern tools.

The New World didn't have good animal candidates for domestication. Almost everything big enough

to be useful is also too dangerous, or too agile.

Meanwhile the fertile crescent to central Europe had cows and pigs and sheep and

goats: easy-peasy animals comparatively begging to be domesticated.

A wild boar is something to contend with if you only have stone tools but it's possible

to catch and pen and breed and feed to eat -- because pigs can't leap to the sky or crush

all resistance beneath their hooves.

In the New World the only native domestication contestant was: llamas. They're better than

nothing -- which is probably why the biggest cities existed in South America -- but they're

no cow. Ever try to manage a heard of llamas in the mountains of Peru? Yeah, you can do

it, but it's not fun. Nothing but drama, these llamas.

These might seem, cherry-picked examples, because aren't there hundreds of thousands

of species of animals? Yes, but when you're stuck at the bottom of the tech tree, almost

none of them can be domesticated. From the dawn of man until this fateful meeting, humans

domesticated; maybe a baker's dozen of unique species the world over. And even to get that

high a number you need to stretch it to include honeybees and silkworms; nice to have, but

you can't build a civilization on a foundation of honey alone.

These early tribes weren't smarter, or better at domestication. The Old World had more valuable

and easy animals. With dogs, herding sheep and cattle is easier. Now humans have a buddy

to keep an eye on the clothing factory, and the milk and cheeseburger machine, and the

plow-puller. Now farming is easier, which means there's more benefit to staying put,

which means more domestication, which means more food which means more people and more

density and oh look where we're going. Citiesville: population: lots; bring your animals; plagues

welcome.

That is the full answer: The lack of New World animals to domesticate limited not only exposure

to germs sources but also limited food production, which limited population growth, which limited

cities, which made plagues in the New World an almost impossibility. In the Old [World], exactly

the reverse, and thus a continent full of plague and a continent devoid of it.

So when ships landed in the New World, there was no Americapox to bring back.

The game of civilization has nothing to do with the players, and everything to do with

the map. Access to domesticated animals in numbers and diversity is the key resource

to bootstrapping a complex society from nothing -- and that complexity brings with it, unintentionally,

a passive biological weaponry devastating to outsiders.

Start the game again but move the domesticable animals across the sea and history's arrow

of disease and death flows in the opposite direction.

This still does leave one last question. Just why are some animals domesticable and others

not? Why couldn't American Indians domesticate deer? Why can't zebras be domesticated? They

look just like horses. And what does it mean to tame an animal? To answer that, click here

for part 2.

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