Quinn's population parable (Story of B)


#1

Not sure where this should go.

I am rereading the Story of B, and have developed doubts about the mice parable in the lecture on population. If you have 10,000 mice, and suddenly give them only enough food for 10,000 mice, it seems to me that rather than painlessly the population stabilizing, as Quinn assumes, there would be severe probles before adjustment.

Let’s say that half of the female mice are pregnant at the time. That’s 2,500. Soon, they will produce pups, let’s be conservative and say averaging 4 pups per little (wiki says it’s actually 10-12 pups per litter). So in a month we have 20,000 mice. But the pups are nursing. In another month, we have 30,000 mice living on the same rations as 10K. And as soon as the new pups are weaned, they will tuck into the food supply. It seems to me that Quinn did not account for the effect of new critters coming on board at a fast rate. If in 4 months there are 40,000 mice living on rations meant for 10K, then there will be fighting for food, there will be cannibalism of the pups, there will be starvation of the weakest.

Eventually, the situation will stabilize, as he says, but I think he is wrong that it’s painless.


#2

True, and it’s a heck of a lot more complex when people are involved. That, plus the idea that it’s now “green” to ruin open space with “clean energy” projects, yields little realistic hope for nature’s future.


#3

Interesting conundrum Vera, you may have a point. Elsewhere Quinn & Dr. Alan Thornhill go into something which seems to be related called the ‘demographic trap’ - see the first 10-or-so mins in this vid:

Basically, instead of the scenario you describe of the food being levelled off suddenly, they describe the effects of a drop in the death rate (because of improved health & sanitation etc). The result is similar, with lots of new mouths to feed and only the same resources to go around. In the 3rd world scenario that’s the point where they start importing food to maintain the population increase until cultural changes eventually lower the birth rate to a replacement level with the low death rate (mainly people find they don’t need so many children to help with all the farmwork).

Possibly mice are a bad example, as I think they’re geared to big fluctuations in population size in response to the sudden availability of lots of food, hence the large litters and the ability to give birth multiple times in one year. They’re also a major prey species so any big population increase is quickly matched by increased predation from carnivorous birds, mammals & reptiles, leading to a balancing increase in death rate. The world isn’t as simple as Quinn’s cage, as FiniteEarther suggests (and as I think DQ would recognise)! Would a halt in the year-on-year increase of global food production cause as much trouble for a human population as for a mouse population? Seems doubtful to me somehow, though there could be issues if people were gearing up for a big growth that then failed to materialise.

Fwiw the global pop growth rate has slowed from an approx 2% yearly increase in the 60s to more like 1% in the present day (wiki). So a 0% rate would, I guess, be less of a shock now than it would have been then. Several European countries seem to be coping with a negative growth rate at the moment, but you’ve got to factor in all their food exports which basically outsource this growth to 3rd world countries. The UK had negative growth during the 70s of around 0.07% annually, due mainly to net migration out of the country because of the economic woes of the time, and I think Russia also had a pretty major decline after the collapse of the Soviet Union, so yes it probably won’t be a painless process, associated with all the other aspects of social collapse. Quinn thinks it would be better if made as a conscious global policy decision to arrest food production at a certain level and then start to gradually roll it back. Personally I think there’s as much chance of that happening as yeast cells refusing to eat available sugar, even as the waste build-up threatens to kill them. Sorry if that’s a downer!

best,
I


#4

i’m happy to report that i’ve read several articles recently ‘lamenting’ that millenials in the u.s. are not having nearly as many kids as our predecessors. they’re calling it a ‘baby bust’ and say that we’re now below population-replacement levels. :heart:


#5

Thank you for the thoughts, everyone. It further occurred to me that Quinn’s example does not work at all (where he says that a 100 mice given 100 food portions a day will remain constant, more or less. Baloney. If only 25 of those females reproduce, you have 350 mice in a month… and yes, pretty soon you will have Famine, Cannibalism, War for food, and Pestilence – the horsemen ride in. And they knock down the pop to 100 eventually, but with a lot of suffering. Then, the same happens over and over again… until after gazillion generations the experiment maybe breeds mice who are so full of wildness (wild-associated hormones and neurochemicals) they slow their reproduction. Sort of the reverse of the Russian tame fox breeding experiment. (Those foxes, after selecting for docility, went into heat twice a year, just like dogs).

Joan, there is no happy news about human reproduction – Jevons paradox kicks in, and others fill the void the millennials leave.


#6

Woozletracker, they are right, of course (in the vid). More food, more people (ceteris paribus). I think, however, that Quinn focuses entirely on the access to food when he talks about the feedback loop that functions so well, and not enough on predation. The famous ecological feedback loop goes like this: more food for mice, more mice: more mice, more food for foxes and therefore more foxes, more foxes, more predation on the mice and therefore fewer mice; mouse food rebounds while predators grow less, and the cycle repeats.

I think you are absolutely right that there is no chance of it happening… we are not wired biologically to do it any more than yeast is.