(December 14, 2014 at 7:22 pm)Beccs Wrote:

(December 14, 2014 at 7:10 pm)lifesagift Wrote: But there were so many violent wars... is that the reason?

55 million people died in WW2, by somewhat conservative estimates. That's a tiny percentage of the human population, even 70 years ago.

And those numbers were easily replaced by the boom after the war.

And even with 55 million fatalities, better than 90% were from disease rather than a direct result of warfare.

The Black Death killed 75-200 million people in the mid-1300's - 30-60% of the human population on the planet.

As it turns out, compared to disease, war has been a pretty inefficient killer.

(December 14, 2014 at 7:27 pm)lifesagift Wrote: Surely life expectancy is key? and number of offspring?

Yes to both. As life expectancy increases - due to getting a handle on what vorlon mentioned above (among other things) - the number of children who survive long enough to have offspring themselves is going to increase, creating a sort of snowball effect.

Humanity has gotten itself into a position where the limiting factors for populations of other organisms (predation, loss of habitat, food shortages, diseases, etc) really don't matter all that much.

Yet.

Boru

(December 14, 2014 at 7:27 pm)lifesagift Wrote: Surely life expectancy is key? and number of offspring?

Well, yeah - population grows when the birth rate > death rate. That's kind of tautological.

Number of offspring isn't directly a factor, not as much as you might think. Every couple could have 15 kids, and if only three reached reproductive age, your population growth would be slower than if every couple had four that all reached reproductive age. All else being equal, of course.

It seems to me that mortality is the more important factor, all else being equal.

(December 14, 2014 at 7:39 pm)Cthulhu Dreaming Wrote:

(December 14, 2014 at 7:27 pm)lifesagift Wrote: Surely life expectancy is key? and number of offspring?

Well, yeah - population grows when the birth rate > death rate. That's kind of tautological.

Number of offspring isn't directly a factor, not as much as you might think. Every couple could have 15 kids, and if only three reached reproductive age, your population growth would be slower than if every couple had four that all reached reproductive age. All else being equal, of course.

It seems to me that mortality is the more important factor, all else being equal.

but if they had only one child!?

(December 14, 2014 at 8:01 pm)lifesagift Wrote:

(December 14, 2014 at 7:39 pm)Cthulhu Dreaming Wrote: Well, yeah - population grows when the birth rate > death rate. That's kind of tautological.

Number of offspring isn't directly a factor, not as much as you might think. Every couple could have 15 kids, and if only three reached reproductive age, your population growth would be slower than if every couple had four that all reached reproductive age. All else being equal, of course.

It seems to me that mortality is the more important factor, all else being equal.

but if they had only one child!?

Look at China.

(December 14, 2014 at 8:01 pm)lifesagift Wrote: but if they had only one child!?

Then population isn't going to grow unless we discover immortality.

But look at world population... 1 billion to 7 billion in the blink of an eye !

(December 14, 2014 at 8:07 pm)lifesagift Wrote: But look at world population... 1 billion to 7 billion in the blink of an eye !

An astounding level of technological and scientific innovation has occurred just as quickly and account for much of that increase.

(December 14, 2014 at 8:05 pm)Beccs Wrote:

(December 14, 2014 at 8:01 pm)lifesagift Wrote: but if they had only one child!?

Look at China.

China has never had a universal policy of one-child-per couple. There are so many exceptions that only about a third of the population is subject to the policy.

However, had they done so, their population would shrink. 1 child for every female is not enough to maintain population levels, much less grow them. It's estimated that the population replacement rate in developed countries is ~2.1 children per female (that is, on average, each female would have to have, on average, 2.1 children to maintain population levels).

(December 14, 2014 at 8:07 pm)lifesagift Wrote: But look at world population... 1 billion to 7 billion in the blink of an eye !

Is there something unclear in the reasons you've been given for this?