Name: 人類人口增長--生態學速成班 #3 (Human Population Growth - Crash Course Ecology #3)
Uploaded: 2021-01-14T04:16:29.000Z
Duration: 10 min 54 s
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If being alive on Earth were some kind of contest, humans,

As a population of organisms, we're the Michael Phelps of being

alive, only we have like 250,000 times more gold medals.

Last week, we talked about exponential growth, when a population

grows at a rate proportional to the size of the population,

even as that size of the population keeps increasing.

Well, since around the year 1650, the human population

has been undergoing probably the longest period of

exponential growth of any large animal in history, ever.

In 1650, there were about 500 million people on the planet.

By 1850, the population had doubled to one billion,

and it doubled again just 80 years after that,

and doubled again just 45 years after that.

We are now well past 7 billion now, and counting.

So, think about this: Today there are 80-year olds

who have watched the population of their species on Earth triple.

So, why is this happening? And...how? And how long can it go on?

Let's say you're shopping for dinner, and bear with me,

we're going to relate it back to ecology in a second,

but you have a lot of choices at your grocery store.

You could buy 5 packs of ramen for a dollar or you could buy

some fancy ravioli made by Italian nuns out of organic pasta

for like $20 dollars a pound. They're both noodles.

They're both food. But, you know, with the ramen you get more,

whereas with the handmade stuff it tastes better.

It's a perennial problem in nature, and in our lives,

satisfying the two competing impulses: do I have more,

or do I have the best? Quantity or quality? Tough choice.

Although we're not really aware of it, all organisms

make a similar choice through how they reproduce.

In ecology, we size up who chooses quantity over quality

by something called the R vs. K Selection Theory.

The R vs. K Selection Theory says that some organisms

will reproduce in a way that aims for huge, exponential growth,

while others are just content to hit the number of individuals

the carrying capacity, and then stay around that level.

Species that reproduce in a way that leads to very fast growth

are called R-selected species, because "R" is the maximum growth

rate of a population when you're talking math talk,

Very strongly R-selected animals make a lot of babies

in their lifetime and just hope that they make it.

If some of the babies get eaten or something, no biggie:

On the other hand, K-selected species only make a few babies

in their lifetime, and invest in them very heavily.

"K" in math language is carrying capacity,

since K-selected species usually end up living at population

densities closer to their carrying capacity than r-selected ones.

Of course, things aren't so cut and dry in nature.

Most animals aren't very strongly K-selected or r-selected.

It's actually, you know, a spectrum: Some organisms,

usually smallish ones, reproducing more on the r side,

and others, usually larger ones, on the K side.

Most species are somewhere in the middle.

So, the reason I'm telling you this is to drive home how bananas

it is that humans have gotten to the population size we have:

Because we tend to reproduce way on the K-selected side of the spectrum.

We're pretty big mammals who usually have only a few kids

during our lifetimes, and those kids are a total pain in the butt

to raise, but we put a ton of resources into them anyway.

So even though humans reproduce K-selected-ish-ly,

for the past few centuries, our population growth curve

has been looking suspiciously like that of a R-selected species.

And exponential growth, even for R-selected species,

Well, the short answer is, humans figured out how to raise

our carrying capacity, so far, indefinitely.

And we did this by eliminating a bunch of obstacles that would have

made our numbers level off at a carrying capacity a long time ago.

These obstacles, you will recall, are limiting factors,

and we've managed to blast them to pieces in a few different ways.

First, we've upped our ability to feed ourselves.

Our crazy-rapid population growth started in Europe around

the 17th century, because that's when agriculture was becoming

echanized, and fancy new farming practices like the domestication

of animals and crops, were increasing food production.

From Europe, those agricultural practices and their

accompanying population explosion spread to the New World

and to much of the rest of the world by the mid-19th century.

Another game-changer for the human population

Anton van Leeuwenhoek, Father of Microbiology all around

really smart guy, was the first modern scientist to propose

the germ theory of disease in 1700, and even though it took

about a century and a half for people to take it seriously,

it revolutionized human health, leading to things like vaccinations.

Suddenly people stopped dying of stupid, avoidable stuff

as they had been for thousands of years, which meant that

everybody lived longer: childhood survival rates improved,

and those kids went on to make their own babies and get very, very old.

And we also increased our carrying capacity

We figured out that you can't just sit around

in your own poop and live to tell the tale.