A comment in the “Should I Date a High-Schooler” thread had me wondering. Someone mentions that women are at their most fertile in their teens. I don’t know whether that’s true, but it doesn’t seem improbable. Much of the discussion in the thread revolved around similarity of maturity-level and development rate and compatibility of personality, as well as legality, for the would-be couple. That’s all well and good; I think compatibility trumps numerical age difference every time. However…
This all assumes we can afford that people be happy and well-adjusted in their social settings. What if for some reason humanity was reduced to a small population of a few thousands and we had get the population up as quickly as possible lest we be wiped out? We would have to throw all such luxuries aside and concentrate on survival.
How quickly could we increase the population? How would we arrange things? At what age could the women start bearing children? 16? 15? Younger? What would ‘marriage’ look like: one man, many women?
What are the most rapid historical examples of population growth?
The age of childbearing would be a balance between two factors: Obviously, you’d want to get started as soon as possible, but pregnancies too young carry an increased risk of the baby and/or mother dying in childbirth. I’m not sure what the proper compromise is.
We’re talking about a small enough gene pool as it is. If we’ve got multiple males, we might as well make use of all of their genes. Assuming that modern record-keeping and knowledge of genetics have survived, the optimum would probably be to try for every possible pairing of not-closely-related couples, to mix the gene pool as thoroughly as possible.
The age of childbearing would be a balance between two factors: Obviously, you’d want to get started as soon as possible, but pregnancies too young carry an increased risk of the baby and/or mother dying in childbirth. I’m not sure what the proper compromise is.
We’re talking about a small enough gene pool as it is. If we’ve got multiple males, we might as well make use of all of their genes. Assuming that modern record-keeping and knowledge of genetics have survived, the optimum would probably be to try for every possible pairing of not-closely-related couples, to mix the gene pool as thoroughly as possible.
Are you allowed to use any sort of technology or just the good old fashioned draught method of delivery. If nothing invasive what about fertility drugs?
Assuming women are going to be baby factories and that we retain modern standards of healthcare, assume 8 surviving children per couple or x4 people per generation. With a start population of 4096, the population will reach 1M in 4 generations and 1B in 9.
How long would the generation time be? Would 15 years be a good average? If so, we have 4 generations in 60 years and 9 in 135. I think there’s some sort of assumption in there about family structure though.
15 years would be too short, if we are assuming each woman has 8 kids. If a woman starts having kids when she is 16, and spaces them out to one every 2 years, then the average generation time will be 24 years.
It appears Quartz assumed his 4096 people were 2048 male & 2048 female.
We have to start out with whatever m/f ratio the disaster provided. For (male) fun we can assume any population skew we want. I’d bet one healthy male could probably impregnate 1 female per week. So given a 38 week gestation period one male could keep 38 females perpetually pregnant. Let’s round down to 30 to give the females a little recovery time, allow for miscarriages, etc.
So now our 4096 people could be 132 males & 3964 females. That’d give a big boost to the initial productivity.
BUT … regardless of the male / female ratio of our initial suvivor cadre, the offspring will be the boring old 50/50 we’re used to. So after about 20 years we’d be back to the x4 / lifetime numbers that Quartz used.
Now if we could alter the m/f ratio of the offspring, we could really boost the per-generation productivity.
Which raises a fascinating hijack … Are there any mammal species which have a male/female newborn ratio very far from 50/50? Certainly there are species where only a small fraction of the males produce most of the offspring, but I’m asking about births, not subsequent alpha male behavior.
'Zactly. Unless you’re 14, you can’t quite achieve the Catholic Ideal of one orgasm = one pregnancy. (Let’s all sing along now … Ev’ry sperm is Sacred …)
I suppose initially a near exponential growth may be possible under ideal conditions, at least for a time.
Several developing countries post some fairly impressive population explosions i.e. Congo (ex-Zaire): 10,384,000 (1942); 60,085,000 (2005), Ethiopia: 12,100,000 (1945); 73,053,000 (2005)
Childbearing age starts with puberty, so potentially very young, though mediated by any surviving moral consensus and the risks of such an early pregnancy. With a base population of several thousand it’s unlikely that you’d need to push the envelope that far anyway.
Leaving aside sex-selective abortion and infanticide, the human sex ratio at birth isn’t itself 50:50 but more like 105:100 in favour of males. I’m not sure what the most skewed mammalian ratio is, but wikipedia’s page notes a variety of fish, the Bluestreak cleaner wrasse, where all the offspring are female and the strongest individual in the group changes gender for the purpose of breeding. This leads to a 1:6-8 ratio in favour of females.
Assuming sex selection IVF technologies were still available, you could obviously idealise the post-disaster ratio for the most rapid growth. Equally if you’re prepared to ditch morality altogether you don’t even require the most basic technology to achieve a gender bias, unfortunately still apparent in some areas of the world today.
The evolutionarily stable strategy is to put as much energy into raising male offspring as female offspring. If it takes more energy to raise males or more energy to raise females, the stable strategy is to put equal amounts of energy into both however that results in numbers. If takes the same amount of effort to produce a male as a female then sex ratios should be equal.
The reason for this is simple, the expected reproductive success of a male or a female in a situation where there is an imbalanced sex ratio.
Imagine a scenario with 10 females for every male. On average, males will have 10 times the reproductive success of females. This means that there is tremendous selective pressure for any gene that increases your chance of producing males. And the opposite holds if there are 10 males for every female.
