In Science What Goes Around Comes Around – but sometimes this can take 40 years. By far my kindest mentor was Alan Welford; a slow, sonorous, intensely dignified scholar and clergyman. He was touchingly dismissive of all but one of his own abilities: high intelligence. When he heard that I had support for what eventually became a 20 year longitudinal study he accosted me, in his stately way, and said “Always remember, Rabbitt“ (we never, ever, dreamt of using each-others’ first names) “the most important thing that you can possibly find out is whether clever people keep their intelligence longer than the rest”. A self-satisfied glint signalled that, in his heart, he was already sure of the answer, and of the group to which he belonged, and so of his destiny, but might like to have his faith backed by numbers (though he was never truly at ease with statistics). I am happy that he did indeed live as long and stayed as intellectually sharp as any of us can hope to do.
When others have asked me “Do clever people live longer and lose their wits more slowly” I have always answered that I think that they do, but only because life is unfair from beginning to end. Affluent families tend to have fine plump healthy babies who are better and more wisely fed and educated and so enjoy more prosperous careers and better medical care and survive longer. Many studies show that because declines in our mental abilities are strongly driven by the accumulations of illnesses that will eventually kill us, at any moment in our later lives our rates of change are more closely linked to how far we are from death than from birth. Dying late also allows us to keep our wits longer.
These arguments are not unwelcome to academic colleagues who are (of course quite rightly…..) extremely conscious of their own high intelligence. But I get the feeling from encounters with them that, like Alan Welford, they really hope for much more than this simple story. They seem to feel that intelligence is a transcendent rather than a biological or a neurophysiological quality, a sort of …… Mojo, …… that magics all aspects of life. I have not found that this feeling is necessarily related to any spiritual or religious belief. For example I know that the Holy Irish Christian Brothers who did their best to bash religion and Latin into me did not think in this way because I remember Brother Gleason panting with effort as he told me “I can strap into you Grammar and the love of God, but never any, any, any glint of intelligence”.
Evidence accumulates that the story I have been telling is too simple. A fine study 1,2 found that the intelligence test scores of Scottish schoolchildren who were aged 14 when assessed in 1948 strongly predicted how long they would live and how late they would decline thereafter. This remained true even when differences in lifelong socio-economic advantage and education had been taken into account though, as far as I know, the more crucial and directly interesting health data were not considered. However later work finds that peoples’ reaction times and intelligence test scores predict their chances of survival even after differences in their affluence, education and general health have been allowed for 3
A great part of the enchantment of doing science is that while you live it never stops. This week, 34 years late, I have learned new bits of answers that might have pleased Alan Welford and that will allow me to look my colleagues more directly in the eye if they ask why my work still offers no reassurance about the durability, if not the actual transcendence and immortality of their intelligence.
Paolo Ghisletta and Stephen Aichele, at the University of Geneva,4 have looked again at the Newcastle and Manchester data for 6504 people who had taken the same sets of tests of intelligence, speed of decisions and memory for words and pictures up to 4 times at 4 year intervals over 11 to 20 years. They found, as others had earlier noticed, that individuals who had performed well when they were first tested thereafter lived longer and declined more slowly than those with lower scores on mental tests. Volunteers’ baseline memory and vocabulary test scores did predict their subsequent survival, but more weakly than did their intelligence test scores and decision speeds. As usual women survived longer than men but, provocatively, for men the stronger of these two powerful predictors was intelligence while for women it was decision speed. Within this elite, highly self-selected group of volunteers there were no differences between the most and least prosperous. How fast and bright you happen to be during your lifetime seems to strongly affect how long you are likely to live. Paolo and Stephen also took into account differences in levels of affluence and between the cities of Newcastle and Manchester but this did not change the pattern.
Paolo’s and Stephen’s additional new finding is that volunteers’ chances of survival are not just determined by their estimated baseline intelligence and speed scores at the beginning of the study, and so probably throughout their earlier lives, but also by the rates at which they changed while the study was in progress. Those who declined faster died sooner than those who declined less and more slowly. This was not just because, as other colleagues and I have suggested in an earlier paper, sharp declines (“terminal drops” as they are described by my grimmer colleagues) occur during the few years just before death 5. The rates at which we change over periods up to 8 or 11 years before death also strongly predict how long we have left.
Obviously at least some proportion of the relationship between rate of mental decline and the approach of death must be due to the accumulating burdens of illnesses that can start to affect our bodies, brains and minds long before they kill us. The other, much more tantalising association is between lifetime level of intelligence and speed and probable lifespan. This suggests that the simple relationship between health, longevity and rate of decline does not capture all that is going on. If further work continues to confirm claims from other studies 1,2 that intelligence and speed do not prolong our lives just because they benefit our lifestyles we have a new, rich puzzle to solve: What, precisely, is the Great Good Luck, – the Grand Mojo – of which being quick and clever are only some, and maybe only incidental, manifestations ?
- Deary, I. J., Allerhand, M., & Der, G. (2009). Smarter in middle age, faster in old age: A cross-lagged panel analysis of reaction time and cognitive ability over 13 years in the West of Scotland Twenty-07 Study. Psychology and Aging, 24, 40–
- Deary, I. J., Johnson, W., & Starr, J. (2010). Are processing speed tasks biomarkers of cognitive aging? Psychology and Aging, 25, 219–
- Anstey, K. J., Luszcz, M. A., Giles, L. C., & Andrews, G. R. (2001). Demographic, health, cognitive, and sensory variables as predictors of mortality in very old adults. Psychology and Aging, 16, 3–11.
- Stephen Aichele, Patrick Rabbitt & Paolo Ghisletta (2014) Lifespan Decrements in Fluid Intelligence and Processing Speed Predict Mortality Risk. Submitted Ms. For futher information please contact Stephen Aichele
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- Rabbitt, P., Lunn, M., Wong, D., & Cobain, M. (2008). Sudden declines in intelligence in old age predict death and dropout from longitudinal studies. Journal of Gerontology Psychological Sciences, 63B, P205–