Thursday 7 August 2014

Longevity versus real health - more reflections on mouse utopia


In the late phases of the mouse utopia experiment the birth rate dwindled to zero - but there was a plateau phase when the population numbers remained approximately static because the mice were living to an extreme old age - four years and longer, which is considerably older than mice will usually live in the wild.

Yet these mice were grossly abnormal, indeed pathological, in their behaviour. - in particular what might be termed psychiatric abnormalities that impaired social interaction (and reproduction) including a strange narcissism in some male mice (the 'beautiful ones') which looked like superb physical specimens but did not mate


So we find on the one hand a combination of evidence of cumulative disease, initially manifested in the realm of behaviour - yet on the other hand an ageing population with some animals having a very long life span.


My interpretation is that an increasing average lifespan cannot be interpreted as improving health - indeed increasing lifespan is compatible with a severe reduction in health; especially when health is defined 'biologically' in terms of reproductive success (having sufficient viable offspring to maintain population numbers, and potentially amplify the population when conditions permit).


In Britain in recent decades there has been a large increase in average lifespan (among the native population), including several-fold increases in the length of survival of many groups of ill people. For example, elderly people with moderate to severe dementia may now live for many years, whereas thirty or forty years ago such a diagnosis was regarded as being rapidly fatal.

There is no doubt that modern people have been, and are being, misled by the increase in lifespan - and superficial appearances of youthfulness - into assuming that population health is improving; when in biological terms what matters is the ability to survive and reproduce under given conditions.


Only if modern people - in particular those of reproductive and productive age - were put into the same kind of environment that people of the past lived-in, would we know whether they really do have better health.

In hunter gatherer societies those who lacked mobility would, sooner or later, necessarily be left to die. In agricultural societies, the struggle for survival was extremely severe.

But modern societies shelter pretty much everybody from exposure to extreme heat or cold, dehydration, starvation, epidemic infectious disease and violence; plus the treatment of chronic medical conditions which would soon cripple or kill without continued medication and management.

Therefore, many people (such as myself!) who would been unable to do anything useful or even survive in historical societies, are able to live for many extra decades in modern societies - with all appearances of good health... except for behavioural pathologies and sub-fertility.


My point is that modern people may be much less healthy than they think they are; and that if societal conditions reverted towards those of historical agrarian societies, or hunter gatherer conditions, their low fitness and inability to survive would become very obvious.


Perhaps the increasingly elderly individuals of the terminal phase of mouse utopia may have congratulated themselves on the success of the experiment, and that mice had attained a more comfortable and compassionate level of social organization than in any previous society.

And then they died out; every last one of them.



Boethius said...

In what stage of the mouse utopia the modern world finds itself in your opinion?

Bruce Charlton said...

@B - The parallels are not exact - in particular the population of England is fairly rapidly being replaced from elsewhere - however this is a very approximate analysis:

pyrrhus said...

Excellent point Professor! Your analysis seems to confirm Mikhail Blagosklonny's thesis that aging is a purposeless quasi program. As such, there is no reason to think that longer life is connected to fitness in a Darwinian sense.

Bruce Charlton said...

@py - Indeed. I sometimes emphasize this in lectures by asking whether the men in the class would like to extend their lifespan by an average of several years - and then (before any have a chance to respond) telling them that this can be achieved by castration. This usually gets a laugh.

In other words people can often increase lifespan by various means, but at the cost of reducing (or eliminating) reproductive success.

Edward said...

I wonder if you've read this:

I believe it sheds rather a lot of light on the situation we find ourselves in.