(06-02-2011, 05:31 PM)--Pete Wrote: Not really. You are overlooking the compounding of change. You are arguing on the basis of a linear model, but the better model is exponential.
Why? Growth is exponential. Decline is not. More people are born as a consequence of past births. But fewer people die as a consequence of past deaths, not more.
Quote:For instance, if you assume a constant death rate of 0.85%/year and no births, then in 2110 the projected world population would be approximately 3 billion, the youngest of whom would be 100 years old. Not a realistic result. The problem is that both the death rate and the birth rate depend on not just the population size, but on the population distribution and sex.
I did say that there would be a massive crash after around 50 years, as everyone reaches the age at which mortality speeds up - 50 and older. In a zero-births model, obviously, the lifespan of the human race cannot be longer than a human lifespan. But even in that incredible case, the massive decline would not even start until around 2040, as the first cohort passes their healthiest age bracket. Up until then, population decline would simply be a stable function of existing cohorts dying off at present rates.
Quote:A slightly better calculation gives a world population of 4.8 billion in 2050 if each woman has (on the average) only 1 child. An average of 0.6 would give a population of 4.2 billion.
How? You'll have to show me your calculation - I thought mine was a limit case. No cohort is dying faster, at least until the youngest cohort hits age 20 or so and production slows down, but no new cohorts are being born.
Quote:There are actually some counter intuitive things going on here. For instance, the present death rate is artificially low because of the increase in life expectancy in third world countries.
The idea here is what, that there are cohorts of children and young adults in Africa that would have died as infants, but are surviving, and will die in greater numbers later? Maybe so, but I can't see that having a massive impact on world population numbers. Nontrivial, but not game changing.
Quote:That's the problem with any rate other than zero -- it leads to explosion or extinction.
That's why we need more space... the final frontier. ;-)
-Jester
(06-02-2011, 08:21 PM)MEAT Wrote: It's part of natural order I believe, and I doubt humans are exempt. Although, I don't know how much of a difference it would really make in the end.
We only evolve the mechanisms that were selected for. Some populations regularly reach saturation for their environment, and thus, would gain reproductive fitness by controlling that growth.
Has that happened to humans on an evolutionary timeframe? I would say it has not. Infanticide has been our typical response to population pressures, and aside from issues with killing babies, from a species standpoint, it seems to work well enough.
There is no "natural order" from which we can reason in this fashion.
-Jester