Pop. Principles

From childhood I had assumed human population was growing because the world was not yet fully populated and life was still expanding, but it turns out most recent "garden of Eden scenario" occurred 500 million years ago, and since then the planet has been full and the total biosphere of life slowly shrinking. It turns out that on geological timescales, it does not take very long for any species to reach its limit for possible population on Earth. So, given every niche where life now exists has long been filled to maximum capacity, how does the human population keep increasing? The answer is the same process that allows new species to arise and grow their populations, a process Darwin declared "survival of the fittest" which is basically species creating their own vacancies by out competing or "evicting" other species, resulting in the decline or extinction of other species to make way for population growth. This may explain why as the human population now grows other species face decline or face extinction, but the twist is how this population growth is happening some 300 thousand years after humans first appeared.

It seems like the human population has forever been growing, but any analysis makes it clear growth must stop eventually at some level. The question becomes at what level should growth stop? Do we go for the maximum possible people just before everything collapses, even if average living standards could be far better with a smaller population? With caged hens being farmed for eggs people advocate for a lower free-range population instead of denser living caged hens as it provides a better existence, but does anyone advocate against multinationals and politicians pushing for denser and denser housing for humans in order to allow bigger populations of humans for them to farm? It seems to be accepted that global population growth should stop but claimed that countries who end population growth face economic disaster.

Throughout history, although no other species on Earth has experienced such long term overall population growth, even before the recent population explosion, the human population kept slowly growing. Yes, we recently had an unprecedented population explosion, driven by is hidden by by the near elimination of previously tragic infant mortality, but against the background of long term growth, many of us never didn't even realise their was an explosion. But what drove population growth even before the explosion? What will now happen as the explosion ends?

The main surprise is that life expectancy reveals very little about how long people typically live. From the 1500s till around 1800, life expectancy throughout Europe hovered between 30 and 40 years of age, and it was only as recent as the 20th century, that life expectancy rose from 49.2 to 80.3 years. Yet famous historical figures from 2,000 years ago, typically lived to around 70 or longer.