According to the data in the United Nations paper "Determinants and Consequences of Population Development Trends", from ancient times to the present, our earth has bred a total population of 100 billion to 110 billion.
Many people will wonder, what is the maximum number of people that this blue planet can carry at the same time?
This total should not exceed 16 billion. Because exceeding this limit will cause great changes in the environment suitable for human beings on the earth.
First of all, this total has a very important living environment as a basis, rather than crowded together like captive animals, that is, human survival requires a certain spatial quality.
So, how many people can a region support, in the discipline of geography there are two terms called "population capacity" and "environmental carrying capacity".
Population capacity is the number of people that a country and region can accommodate;
The environmental carrying capacity refers to the number of people that a country or region can sustain to support under the condition of ensuring that it meets the standard of living standards by using local resources.
According to the earth's own capacity, the land area that can survive for human beings is only 149 million square kilometers, accounting for only 29.2% of the total area of the earth, which also includes the Antarctic continent and many islands.
According to statistics, there are currently nearly 1.4 billion hectares of arable land on land that can grow food.
Let's assume that all humans are vegetarian and don't take into account the food needed by livestock for the time being.
According to the report of the Food and Agriculture Organization of the United Nations, global food production in 2020 is about 2.742 billion tons.
Then, a person eats about 1.5 kilograms of grain a day and about 547 kilograms of grain a year.
10 billion people were × 2.742 billion tons× × 2÷ 547 ≈ 200 million tons.
As a result, 1.4 billion hectares of arable land can feed about 10 billion people.
To reach the limit of 16 billion people, it is necessary to use the photosynthesis of all plants on the planet.
Because the photosynthetic energy of plants converts solar energy into chemical energy, it is stored in the organic compounds it forms.
The chemical energy stored in these organic matter, then, in addition to being used by the plants themselves and all heterotrophic organisms, is more importantly a source of energy for human nutrition and activities.
If the nearly 40 trillion watts of energy absorbed by the photosynthesis of all plants can be converted into human food, then the entire earth can support a total population of up to 16 billion.
However, in such a crowded environment, other life forms will be almost completely eliminated.
At this point, an unknown conundrum arises: if 16 billion people live on Earth at the same time, what changes will occur to human behavior at this time?
A thought-provoking experiment on animal behavior:
In 1968, animal behaviorist John Calhun used a metal fence 2.7 meters long and 1.4 meters wide to make a closed nest for rats with automatic projectors of water and food.
The maximum capacity of this nest was 3800 rats, and John put 4 pairs of rats in it.
In the beginning, John called this nest a utopia of rats, and rats can do any activity in it, but they can't come out.
The first 4 pairs of rats live very moistly, but you know, the reproductive ability of rats is particularly fast, and after 55 days, their number will double.
There are more rats, and their days in this nest are naturally not as moist as before.
By day 315, the number of rats in the nest had reached 610, the highest number of rat populations in John's experiment for the first time.
Since then, the rate of rat reproduction has slowed down significantly, doubling every 145 days.
To make matters worse, the behavior of the rats in the nest became chaotic.
The male rat became particularly aggressive, no longer performing the task of succession, but fighting everywhere to grab the territory, the defeated male rat lost its social status, and chose to avoid social interaction and became depressed.
In order to be able to support the family, the female mouse quickly weaned the mice, and even expelled them, allowing them to carry the burden of survival prematurely.
Therefore, these little mice are first abandoned by the male rats and then by their mothers, and they have no idea how to survive in the nest.
But what is interesting is that these chaotic behaviors of parents have actually been inherited.
By day 600, the rats' social ecosystem had completely collapsed and their behavior had been completely degraded.
96% of the young mice died, cannibalism, the female rat ate the mouse, and the male rat mated with the male mouse.
At this time, a special group of rats was produced, who ate, slept, and combed their hair every day, and at other times they had nothing to do and had no interest in the outside world.
It goes without saying that in the end all the rats in the nest went extinct.
Many see John's dark experiment as the ultimate metaphor for the fate of humanity on Earth.
In fact, this experiment seems to be somewhat similar to the human living environment, but we humans have wisdom, and the benefit of wisdom is that we can solve difficult problems.
For example, we can build taller skyscrapers and reduce overexploitation of land;
More nutritious and convenient foods can be developed, reducing the need for arable land;
Colonize the moon and Mars, opening up new habitation environments.
With the development of human science and technology, these living environment problems will definitely be solved by us one by one.
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