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Comment by cft | Hacker News Reader

because there are fewer and fewer children. http://reason.com/blog/2014/12/05/us-birth-rate-hits-all-tim...

I found the interview at the bottom of that article completely surreal. A couple of talking heads applying reason to question of whether the world has enough people or not (and apparently deciding that it doesn't have enough), when all they needed to do was buy a plane ticket to Bangladesh.

> when all they needed to do was buy a plane ticket to Bangladesh.

As someone from Bangladesh, I have to say it's not quite so simple. Does the country need more people in general? No. Does it need more more parents to spend the time, money, and energy it takes to raise highly-educated kids that are going to be the backbone of the economy in a couple of decades, and to do that in Bangladesh instead of moving abroad? Absolutely!

But net immigration into the US, so the population is actually increasing.

The point is many people forego having children, and then keep dogs or cats to fill in their need for nurturing.

>1.86 babies, well below the 2.1 needed for a stable population

Should it not be 3 babies or over? Maybe my lack of statics knowledge is my problem.

But if two parents have two kids that's zero population growth if they have three kids that means they've replaced themselves plus added one more person to create population growth.

"stable" here means zero population growth over the long term, which actually requires a little above 2 per couple to account for people who die before being old enough to parent children. 2.1 is the common approximation for that.

I see what you mean stable versus growth I just assumed growth was needed to survive not just stability.

But people live after they reproduce. Having 2 children, and every 2 in the next generation have 2 more, etc, means population continues to grow. A steady state is reached, but as lifespan increases so does population. The obvious limit is, if lifespan is infinite, then 0 children is the only number that permits a stable population.

Eventually the older generations die. That stabalizes things.

The average human lifespan is a relatively fixed sized buffer. Since everyone who is born eventually dies, input matches output, and there's no population increase other than the average lifespan (and thus the buffer size) increasing.

I don't understand your question.

Stability and growth are different things.

Not all couples need to have extra babies to have growth.

Why did you bring up growth?

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