Handedness Aging And Lifeexpectancy

The reason for the age related trend is controversial. (See also Chapter 4 of this volume.) The elimination hypothesis, that non-right handers die younger than right handers so none remains alive if one goes sufficiently far back in time (see Ashton, 1982, Coren & Halpern, 1991; Halpern & Coren, 1988, 1990, 1991), has been severely criticized (see Anderson, 1989; Kuhlemeier, 1991 ; Wood, 1988; commentaries in The New England Journal of Medicine, vol. 325, No. 14, 1991; Harris,1993; and reply by Halpern & Coren, 1993).

The evidence offered by Coren and colleagues for reduced longevity in left handers was of two sorts. First, the mean age of death of consistently left-handed baseball players was slightly younger than that of left-handed players (Halpern & Coren, 1988). The findings were not replicated by Fudin, Renninger, Lembessis, and Hirshon ( 1993) nor by Hicks, Johnson, Cuevas, Deharo, and Bautista (1994) in their own analyses of baseball data (see also Lembessis & Fudin, 1994). Supporting findings have, however, been claimed (Rogerson, 1993).

The second type of evidence (Halpern & Coren, 1991) came from a study of the mean age of death of right handers and non-right handers (determined by answers given by relatives of the deceased to three questions) in the state of California. Mean age of death was 9 years younger for non-right handers.

Annett (1993) has drawn attention to a weakness in any attempt to explain a decline in dextrality with increasing age in terms of reduced longevity of left handers. She argues that "The fallacy rests on a failure to distinguish between criteria used to define left handedness in the early and the later studies. In the first half of this century, the pressures against left handed writing were so well-known . . .that evidence of left handedness was sought in actions other than writing" (original italics).. In a sample of people dying in any one year, the oldest sinistrals would have been shifted to dextrality and counted as right handers, while those recorded as left handers would be on average younger It is not that left handers die younger, but that left handed writers are younger than right handed writers in the population" (pp. 296-297). She has since published data confirming this for the U.K. (Davis & Annett, 1994).

An alternative hypothesis, that society has in general become more tolerant of deviations from consistent handedness in recent years (the social-modification hypothesis), has been more widely accepted, not that this is the only alternative possible. Porac ( 1993a) identified 6 different hypotheses but on the basis of her own data favoured "a combination of two developmental hypotheses, one postulating a trend toward increased consistency of preferred hand use and the second proposing the gradual covert shaping role of a right-based environment" (p. 709). It is perhaps not well appreciated that even at the present time some 11 per cent of (Canadian) individuals (Porac, Coren, & Searleman, 1986) experience overt pressure to switch hand, usually from using the left to using the right. Porac, Rees, and Buller ( 1990) conclude that "approximately 8% of the within-cultural variability in adult handedness scores can be explained by knowledge of overt environmental pressures. This figure rises to 23.5% when one examines cross-cultural variations in handedness patterns" (p. 285).

It is commonly found in family studies of handedness that there is a greater proportion of non-right handedness among the filial than the parental generation (e.g., Annett, 1979, 1994; Ashton, 1982). This generation effect has been found not only in recent studies but in earlier ones, too. This implies that a relaxation of social presure against left handedness in recent times cannot be the only mechanism underlying a reduction in left handedness with age. However, if the different manifestations of sidedness are indeed biologically related and if the elimination hypothesis has some credence, then one might also expect to see an age-related effect in footedness, eyedness or earedness, which presumably are not subject to social control. It is therefore of interest that Dargent-Pare, De Agostini, Mesbah, and Dellatolas (1992) reported finding an age effect in eyedness and footedness (see also Gabbard & Iteya, 1996; Porac, 1996) in a large scale study (n=5,199) of individuals from different countries. A similar effect was reported by Porac, Coren, and Duncan ( 1980). It is difficult to see why eyedness, for example, should be subject to social pressure and these data therefore offer a measure of support for the elimination hypothesis, which has not yet been unequivocally disconfirmed (see Hugdahl et al., 1993; 1996).

Because it has been claimed that left handedness is associated with life-threatening conditions such as breast cancer (Kramer, Albrecht, & Miller, 1985), it would not necessarily be surprising to find that left handers die earlier than right handers despite the fallacy highlighted by Annett ( 1993). Even less dramatic associations between non-right handedness and smoking (Harburg, 198I), alcoholism (Bakan, 1973; London, 1986, 1989; London,

Kibbee, & Holt, 1985), responsiveness to centrally active drugs (Irwin, 1984; London, 1986), auto-immune disease (Geschwind & Behan, 1982; Geschwind & Galaburda, 1987) and risk of accident (Coren, 1989; Halpern & Coren, 1991) might be expected to have some effect.

With regard to auto-immune disease, however, a thorough review of the literature (Bryden, McManus, & Bulman-Fleming, 1994a; see also commentaries and reply by Bryden, McManus, & Bulman-Fleming, 1994b) concluded that although "there seem to be real associations between handedness and some immune disorders ... some of these associations ... follow the pattern hypothesized by Geschwind and Galaburda, while others ... show the reverse pattern" (p. 152).

How to Stay Young

How to Stay Young

For centuries, ever since the legendary Ponce de Leon went searching for the elusive Fountain of Youth, people have been looking for ways to slow down the aging process. Medical science has made great strides in keeping people alive longer by preventing and curing disease, and helping people to live healthier lives. Average life expectancy keeps increasing, and most of us can look forward to the chance to live much longer lives than our ancestors.

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