Tuesday, July 10, 2007

Just replace yourself, childwise

Been meaning to post about this for a while, but was too lazy.

In an effort to stem the tide of population growth its often suggested people only replace themselves.

Let's do the math.

This year there are two people in the world. A man and a woman.

They have two children or "replacements".

These children marry and have two "replacement" children for them and their spouse.

See the problem here? If the first two people are still alive, there are now 8 people in the population where there were initially only 2.

Barring accidents and other non-natural deaths, and considering multiple births, the population grows and it grows a lot.

The only way to keep the world's population under control is for a couple to have only 1 child.

Surprisingly, I had to quit looking for a "suitable" picture for this post. It had to be 3 generations which totaled 8 people and there were none I could find.

I did post a picture of a couple with only one child. That might already have changed or be in the process of changing, of course.



Blogger Mike said...

I googled "replace yourself" and found your blog.

The big hole in your maths is that people die. The population would ultimately decrease until the world comes back to balance. And the 'survival of the species' instinct kicks in again.

10/01/2009 11:08:00 AM  
Anonymous Anonymous said...

I was googling "overpopulation" to look at funny comics when I came across your blog...

The idea of "replacing" yourself does work, actually. Think about it: a man marries a woman and has two children to replace him and his wife. Then their children marry and have two children each. These children (the F2 generation) replace the original couple's children and their spouses. Each generation only produces enough people to replace the producing generation. Mathematically:
1 father + 1 mother = 2 children
parents die
1 child + 1 spouse = 2 children
1 child + 1 spouse = 2 children
2 children + 2 spouses die
So.. the deaths cancel out the births. You're still left with a net gain of zero:
6 children - (2 parents + 2 spouses + 2 original children) = 0

It only looks like there is population expansion because it branches to other people's lineages. There's no growth, though. The only way this can work, however, is if each person in a population only has two children.

The "replacement" method works if you want to sustain a population. If you want to cut a population in half, you would need to only have one baby per couple. So... a population of 200 people (100 males and 100 females) would produce one child per couple (100 children) to spread their genes to the next generation, thereby reducing the population.

12/14/2009 12:43:00 PM  

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