aging

An introductory review of the literature on why people’s levels of happiness followed a U-shaped curve  in the vast majority (72) of countries researchers have looked at, from Azerbaijan to Zimbabwe.  The nadir of the U is always in the mid to late 40s, with people emerging from the low period in their 50s. They found this curve held its shape  irrespective of a person’s’ socio-economic status, whether were divorced, or were facing changes in jobs or income, or whether there were children in the house or not.[br]

“So I, the fires that lit once dreams
Now over and spent,
Lie dead within four walls
And so now love
Rains down and so enriches some stiff case,
And strews a mind with precious metaphors,
And so the space
Of my still consciousness
Is full of gilded snow,
The which, no cat has eyes enough
To see the brightness of.”

From Ezra Pound’s Middle Aged

Michelangelo’s sculpture in marble ‘Awakening Slave’ was completed when he was 48 years of age – in his middle age.

It’s entitled ‘awakening’  but it looks like he’s sinking in quick-sand – which is perhaps metaphoric for widespread experience of middle age.

The ‘mid-life’ crisis is an idea that has empirical support in a study by Arthur Stone (Stony Brook, NY) and colleagues, reported in their 2010 PNAS paper  ‘A snapshot of the age distribution of psychological well-being in the United States’.

In their study they look at psychological well being as a function of age over the lifespan. Psychological well-being (WB) includes a person’s overall appraisal of his or her life (Global WB) and affective state (Hedonic WB). They used a Gallop telephone survey of over 340,000 people in the US to get averages of both Global and Hedonic WB by age. Ages in this huge sample ranged from 18 to 85.

The nadir of middle age

What did Stone and colleagues find?  All positive well-being measures – overall life appraisal (Global), Enjoyment and Happiness –  showed U-shaped patterns with their nadirs in middle age (between around 40 – 60, with the lowest points in the 50s). It’s the same ‘U’ for both men and women. Here’s the graph for overall life appraisal.

Fig. 4.

Overall appraisal of life

That’s a striking rise in the overall appraisal of one’s life after one’s 50s for both men and women! It just continues to rise and rise into the mid 80s, where it peaks over the entire life-span. And this is despite the obvious deterioration of objective physical well-being, which previous studies have confirmed.

Enjoyment and Happiness

Cognitive decline & average earnings

As with physical aging, cognitive decline will have taken it’s toll by 80 (see graph below), with quite dramatic drops in IQ, but apparently this doesn’t affect a person’s global well-being, happiness and enjoyment too much – which is something to keep in mind when you hear about all the doom and gloom associated with old age.

Cognitive Aging

And subjective well-being and life evaluation seems to have little to do with average earnings as a function of age.

graph : age wages

Figures are for gross (i.e. before deductions) full time weekly earnings in the UK in April 2011 (source ONS).  Earnings tend to max out in middle age, not just in the UK but in the US and elsewhere.

Youthful angst

But there’s a different pattern for some of the negative well being measures. Sadness has a ‘bump’ pattern that is the inverse of the happiness ‘U’ as you’d expect. Stress and anger drop quite dramatically with age. People are by a long way at their most stressed and angry when they are in their early 20s. This period  is the zenith of angst in life – which is interesting given how positively this age group rate their happiness and overall life quality.

(As an aside, this shows that anger has a very different kind of dynamic to sadness – even though both may be considered ‘negative’ emotions.)

Negative well being indices

The angst of youth

Women have a harder time, but report more global well-being

You can see from these graphs that women experience more stress, more worry and more sadness throughout the lifespan (compare with anger where there is no gender-difference).  Despite this striking inequality, women  report higher levels of Global WB (overall life appraisal)  from the mid 20s through to the mid 50s  and again from the mid 70s onwards (see above). Men look like they are consistently enjoying themselves a bit more than women though!

What causes the well-being ‘U’ and increasing well-being with aging?

Stone and colleagues considered a number of hypotheses that might explain the well-being ‘U’ function – for example that WB improves when children leave home by reducing family conflict and family burden. The variables they looked at as ‘co-variates’ over the lifespan  included:

  • Time with children.
  • Time with partner.
  • Being unemployed.

They  found that controlling for these variables:

only marginally altered the pattern of the association of WB with age, indicating that they do not individually or collectively account for much of the age relation

None of these factors explains the ‘U’ of well-being.

So the overall WB-age pattern calls out for explanation. Why are older people, on average, happier and less stressed than younger people? Stone and colleagues’ US population study reveals a pattern that is remarkably consistent across countries.  Results published by Oswald & Blanchflower in the Journal Social Science & Medicine (paper here), showed that people’s levels of happiness followed a U-shaped curve  in the vast majority (72) of countries the researchers looked at, from Azerbaijan to Zimbabwe.  The nadir of the U is always in the mid to late 40s, with people emerging from the low period in their 50s. They found this curve held its shape  irrespective of a person’s’ socio-economic status, whether were divorced, or were facing changes in jobs or income, or whether there were children in the house or not.

Three theories  are consistent with the ‘wellbeing-over-the- lifespan ‘U’ function:

  • Baltes’ theory of increased “wisdom” and emotional intelligence with age (at least through middle age), wherein decreased negative affective states could be a result of increasing wisdom.
  • Carstensen et al.’s socioemotional selectivity theory, wherein older people have an increased ability to self-regulate their emotions and view their situations positively.
  • A “positivity effect,” wherein older people recall fewer negative memories than younger adults.

But explanations are up for grabs.

A more complete understanding of the determinants of aging on WB, including potential psychological, social, and biological explanations, deserves our attention.

Stone et al. 2010

All great apes may feel the ‘U’

Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being has just been reported in Weiss and colleagues’ 2012 PNAS paper ‘Evidence for a midlife crisis in great apes consistent with the U-shape in human well-being.

In this study the researchers showed that a similar U-shape exists in 508 great apes (two samples of chimpanzees and one sample of orangutans) whose well-being was assessed by raters familiar with the individual apes.

The apes covered all age ranges, and their ‘subjective well being’ was rated through a survey answered by their keepers or those who knew them well. The survey covered four criteria:

  • the animals’ overall mood
  • how much pleasure they got out of socializing
  • their success in achieving goals such as obtaining food and objects they desire
  • how happy the keeper would be if he or she were that animal for a week

Here are the averaged and standardized well-being ratings averaged over the different samples of great ape species. Apes, with shorter life spans, reach middle age before humans do – in their late 20s to mid 30s.

It’s the well-being ‘U’ function all over again!

How do humans fit in?

Great apes are members of the biological family Hominidae. This  includes: chimpanzees, gorillas, orangutans, bonobos…… and humans.

 

Evolutionary origins of well-being?

It’s pretty clear that chimpanzees and orangutans go through a ‘mid-life crisis’, just like humans – and have the same well-being ‘U’ function over the lifespan. This suggests that economic and cultural conditions specific to humans – or even what is unique to human biology such as family life  or in-group cooperation – does not have much to do with the overall dynamic of how happy we feel over our lifespans. The origins of this happiness trajectory lie in a common great ape ancestor!

Weiss and colleagues conclude (provocatively):

Our results imply that human well-being’s curved shape is not uniquely human and that, although it may be partly explained by aspects of human life and society, its origins may lie partly in the biology we share with great apes.

…studies of age and well-being in other species of great apes and studies examining possible fitness costs of high midlife well-being in chimpanzees, orangutans, and humans would lead to a greater understanding of its evolutionary origins. These and other comparative, evolutionary approaches offer applications beyond the midlife nadir in happiness and could affirm Darwin’s (29) view that “He who understands baboon would do more towards metaphysics than Locke.”

Outstanding questions

  • What factors determine this ‘U’ well-being function that we share with other great apes?
  • Do older chimpanzees and orangutans also self-regulate better their emtional states better as they age?  Are there shared changes in cognition that play a role?
  • Do hormone concentrations over the life-cycle play a role?
  • Is there actually a selective advantage for the ‘U’ curve?
  • Is there a socio-ecological explanation based on competition for status or mates?
  • Do other great apes exhibit the same sex differences in well-being, stress and sadness?

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