Wednesday, 12 August 2015

If humans are recapitulating mouse utopia, what is the approximate timescale for extinction?

In the Mouse Utopia experiment, an optimal environment with ample food, space, temperature, no predation etc. was created for 8 pairs of healthy breeding mice - but eventually the entire colony died, every single mouse - because after about two and a half years there were no more conceptions. The colony became sterile.

Before they died there were several phases

Phase A - 104 days - establishment of the mice in their new environment, then the first litters were born.

Phase B - up to day 315 - exponential population growth doubling every 55 days.

Phase C - from day 315-560 population growth abruptly slowed to a doubling time of 145 days.

Phase D - days 560-920; population stagnant with births just matching deaths. Emergence of many pathological behaviours.

Terminal Phase - population declining to zero. The last conception was about day 920, after which there were no more births, all females were menopausal, the colony aged and all of them died.

This is interpreted as a consequence of mutation accumulation leading to extinction from mutational meltdown:


As far as I can gather, mice are fully ready to reproduce at about 4 months, so the average generation time is probably about 5 months which is about 150 days.

So, starting with 104 days as zero - when reproduction began; we can convert the above timings into mouse generations

Phase B exponential growth doubling every 55 days lasted 201 days, = 1.3 mouse generations.

Phase C exponential growth doubling every 145 days lasted a further 245 days = 1.6 mouse generations.

So population growth phase in utopian conditions lasted only 3 mouse generations. 

Phase D of population stagnation phase lasted a further 360 days = 2.4 mouse generations

Therefore, the last conception (and de facto inevitable extinction) was 816 days after breeding commenced = 5.4 mouse generations.


Human generations are conventionally 25 years, although these have slowed to about 30 years in Western countries in the past several decades - but let us therefore give two values - one for 25 year, and the other for 30 year human generations.

If we start at 1850 as the date when the Industrial Revolution seems to have become certainly established and child mortality rates began to drop rapidly, and start counting generations from that point, and if humans were made like mice (which they are not!)...

We would then predict that human population growth phase (B & C) would last three generations up to 1925-1940 

And the stagnation phase (D) for another 2.4 generations - with 5.4 human generations taking us up to 1985-2012.


Well, clearly English people did not stop conceiving three years ago, because babies are still being born to native English - albeit not at a high rate!

I have previously guesstimated that the English situation  was that the slower growth phase c began in about 1920 (not about 1880) and the plateau phase began in about 1970) not 1930-ish

So maybe England is lagged about 40 years, because 1. we are not mice, and 2. our mouse utopia emerged only incrementally and was probably not complete until about 1950.

So we do not need to worry about mutational meltdown and de facto extinction (i.e. the final English child of English parents and ancestry being conceived) for, oh, another thirty or forty years...


Nonetheless, I draw the following lessons.

1. Assuming the decline and extinction of mouse utopia was due to mutation accumulation leading to mutational meltdown - then it happened very quickly indeed: only mouse 5.4 generations to the final conception, with half of that being stagnation.

2. The decline in rate of population increase after only 1.3m mouse generations suggests that the effect of relaxed natural selection and mutation accumulation leads to genetic damage immediately, in the very first generation.

3. Although humans (maturing over 14 years and with a natural life expectancy about 70 years) are built to last longer than mice (maturing over 4 months and living about 2 years) - this may mean that humans are more vulnerable to mutation accumulation - because we have a more prolonged and multi-phasic development and depend on extremely-complex brains which use many genes make and to function, and constitution large mutational targets.

4. In mouse utopia, the mouse environment, shelter, food, hygiene etc were all managed by humans - and did not depend on the mice doing anything much for themselves except east, sleep, fight, groom and reproduce (until they altogether lost interest in sex)- but humans depend on other humans for survival.

When the human population is damaged from mutation accumulation, this will destroy the 'utopian' environment. If this destruction is severe enough and comes early enough- then mutational meltdown will be avoided.

But if there is a generational lag - and utopia is maintained sufficiently that further mutational damage to younger generations continues to accumulate - then this will hasten the meltdown and extinction; because by the time utopia comes to an end, the younger generations will be unfit to survive the harsher conditions.

Have a nice day!


Valkea said...

Was there additional factors which caused mouse extinction, like overcrowding and consequent social stresses?

Bruce Charlton said...

@V - The author interprets the experiment in terms of overcrowding being the cause - but this seems obviously nonsense.

The environment was designed for 3840 mice, but the population peaked at only 2200.

And it is hard to see how overcrowding could cause extinction of every last mouse - if the cause of population decline was overcrowding stress, then as the population declined, one would have assumed that the mice would have begun breeding again. Why was every mouse affected? Surely some would have been resistant to the psychological stress of the (non-existent) overcrowding and would have continued to breed - even if more slowly.

The scientists also reported anecdotally that the mice seemed less and less intelligent in their behaviour, they seemed demotivated, their behaviours became maladaptive.

Eric Ruttencutter said...

You may like to read the new science fiction novel Aurora by Kim Stanley Robinson, which details the difficulties encountered by the crew of a multi generational starship, including decreasing IQ, slower reaction times, different evolutionary rates between microbes and humans, etc.

Wade said...

So what would a solution look like? Ending socialism? More immigration to put pressure on the native population? Eugenics?

Bruce Charlton said...

Wade - No solution. Just acknowledge and cope and best we may.

Cloudswrest said...

Wade - No solution. Just acknowledge and cope and best we may.

Well in another decade or so the "Gattaca" solution, using improved versions of CRISPR or whatever, should be available (if only to self selected groups) to do what Cochran calls "spell checking the genome" to scrub the zygotes of each generation of deleterious mutations. These groups risk suffering the "crap pot" or "tall poppy" syndrome though.

Cloudswrest said...

It would be interesting to redo the mouse utopia experiment with a built in survival fitness requirement. Perhaps an inclined freewheeling treadmill that must me surmounted in order to get to the food (with perhaps an electro-shocking floor in the mess hall that activated after feeding to keep them from hanging out and/or residing there after feeding). Provisions might have to be made for nursing mothers, etc.

Bruce Charlton said...

@C - I don't believe that genetic engineering will work - WD Hamilton explained why he thought it would not work. The geneticists are (as a species, overwhelmingly) an appallingly uneducated, ignorant and incompetent bunch, so their opinion is not worth asking.

But, as always, we need to consider who 'they' are that are being expected to engineer future humans, and what their motives would actually be - considering what they are at present.

Yes - it would be great to redo mouse utopia, many times and in many ways. For a start, there would need to be a straight replication to see if the same result happened, monitor genetic change, intelligence etc.

MarkN said...

Could you summarise Hamilton's thought on why genetic engineering would not work. Or, point to non paywall.

Bruce Charlton said...

@MN - You can read some of it on Google Books, WD Hamilton, Narrow Roads of Gene Land - Volume 2 - the chapter entitled The Hospitals are coming.

Kjetil Sevenius said...

Interesting Experiment, but it only proves that inbreading is not god for the geene pool, as we have many historical examples of from small communities, e.g european royal families of last century. With a larger starting population I'm convinced the experiment would show that the mice would not degenerate even with indefinate generations. What is created here is a small homogenous and synchronized gene pool which will fail simulatiously in the whole population, hence the extinction. Actually this experiment is only a mouse utopia from an external perspective. If one takes into account the mice itself one would realise that the selection mechanism is indeed highly present in the form of malfunctioning geenes. The malfunctioning of the geenes would be comparable to a cataclysmic natural disaster like the meteor hitting the earth 65 million years ago, wiping dinosaurs of the map.

Bruce Charlton said...

@KS - There is no problem with inbreeding so long as the offspring are under strong selection such that only a minority of the fittest breed.

There have been more than 200 years of intensive inbreeding (and crossing, of course) among agricultural animals without extinction, and indeed with considerable functional improvements.

The key variable is not the fertility, but the mortality.