Wednesday, 12 August 2015

A timescale for human extinction - a speculative extrapolation from mouse utopia

I would not advise reading the above post if you are feeling despondent, especially not if you are also English.

Note - Sorry! I initially posted the wrong link for this post: now corrected.


knifecatcher said...

Central Africa is in a different category.

List of countries by median age

Zambia 16.7
Malawi 16.3
Mali 16.0
Uganda 15.5
Niger 15.1

Bruce Charlton said...

@k - Indeed. However, the lag may not be all that great, because although Sub Saharan Africa industrialized maybe up to 100 years later than England; the African generation time is shorter, probably spontaneous mutation rates per generation are higher, and African population growth has been created and is sustained by the Western populations (especially by medicine and public health and hygiene) - those now far advanced in mouse utopia.

Nathaniel said...

@Bruce - How does this function among the upper classes/aristocracy? Assuming they've had the highest fertility rates for the longest, with the most surviving children (but assuming otherwise better adaptability, at least at one time) - does it just sort of balance out?

Bruce Charlton said...

@Nathaniel - On the one hand, the upper classes would have started out (before the industrial revolution) with a lower mutational load (as reflected in higher intelligence and greater reproductive success) - but the upper classes were the first to experience the relaxation pof purifying natural selection; and if this inflicts damage as quickly as Mouse Utopia suggests then there should have been a rapidly obvious effect on reproductive success. And indeed, the demographic transition to lower fertility did start first in the upper classes, went into subfertility first in the upper classes, and has gone furthest in the upper class (highly intelligent) women (who have an average fertility rate of about 0.5 children per woman unless traditionally religious - which few are). It is possible that the incidence of sexual pathologies (sexual development being probably sensitive to mutation accumulation) rose first in the upper classes. So overall, I think the data broadly fits the predictions of mutation accumulation.

Anonymous said...

The experiment started with 8 pairs of mice. How much might inbreeding have played a role?  Were the original pairs even of distinct stock? If mice inbreed more readily than we do,  or the ones in the experiment were related in the first place, maybe we can credit ourselves another generation or two for being 'not mice'.

But then, how many nuclear engineers are we producing these days to run or replace all those reactors tomorrow?  Details, I know,  but that could accelerate mutation accumulation; a balancing debit on our 'not mice' ledger, I suppose.


Bruce Charlton said...

@Bill - I expect inbreeding had a role - indeed all lab animals are inbred so as to make them phenotypically as homogenous as possible. Inbred, but they are selectively bred - these mouse in the utopia experiment were not selectively bred, and I think that was one reason they declined so fast.

It would be daft to make too much of the mouse utopia experiment, but equally daft to ignore it. The facts that the mouse reproductive rate declined before two generations had elapsed, and that every last mouse died out despite utopian conditions, were quite unexpected and need careful consideration.