Behavior OnLine Forums - IQ Differences and Suicide

I stumbled over the following...

Tomassini later rebutted his observation about twin's IQ and cited their results with 21,000. (good gawd!). On the other hand, I think Segal's "Entwined Lives" notes a small but consistent drop in IQ with twins...

From another world, there are consistent data linking IQ with ancestry. And the distinguished George Howe Colt (November of the Soul: The Enigma of Suicide, Scribners, 2006) rambles at some length that Blacks, despite poverty and education problems, rarely kill themselves. Colt reaches no conclusions but, judging from the general tone of his book, would probably skip Voracek's data.

Also note: Catanzaro proposed, perhaps as early as 1981, that suicide is a product of inclusive fitness. Some of his data from '91 & '95 are summarized in Buss, Evolutionary Psychology, 2004. The business of a "threshold IQ" is new to me.

JB

"BMJ 2003;327:1168 (15 November), doi:10.1136/bmj.327.7424.1168-a

"Letter

"Risk of suicide in twins

"Intelligence of twins and singletons may explain risk

"EDITOR: Tomassini et al presented evidence for a lower suicide rate of twins compared with singletons.1 However, they did not present any data supporting their preferred explanative factor ("strong family ties") for this finding, and their explanation is therefore speculative. Other causal factors need to be considered. I give one example.

"According to de Catanzaro's evolutionary theory of human suicide, a threshold intelligence is necessary for suicidality.2 A corollary of this hypothesis is that human intelligence and suicide mortality should be positively related.

"This prediction has been confirmed in an ecological study of 85 countries.3 National intelligence is significantly positively related to the national suicide rate, and ethnic differences in intelligence correspond to ethnic differences in suicide rates. Furthermore, excess suicide prevalence has been observed in the highly gifted.3

"Following these convergent strands of evidence it would be expected that population subgroups with a lower intelligence level than the generality also show lower suicide mortality than the generality. It has long been known that mean scores in intelligence tests are some 6 IQ points (or 0.4 standard deviation units) lower for twins than for singletons.4 5 The current finding of Tomassini et al is consistent with the expectation that subgroups that are on average less intelligent than the general public also have a reduced suicide risk compared with the general public. It seems that the intelligence of twins needs to be considered as an explanatory factor for the current finding.

"Martin Voracek, research resident

"Department of Psychoanalysis and Psychotherapy, "Statistics and Documentation Branch, University of Vienna Medical School, A-1090 Vienna, Austria

"martin.voracek@akh-wien.ac.at

"References
"Tomassini C, Juel K, Holm NV, Skytthe A, Christensen K. Risk of suicide in twins: 51 year follow up study. BMJ 2003;327: 373-4. (16 August.)
de Catanzaro D. Suicide and self-damaging behavior: a sociobiological perspective. New York: Academic Press, 1981.
Voracek M. National intelligence and suicide rate: an ecological study of 85 countries. Pers Individ Dif (in press).
Record RG, McKeown T, Edwards JH. An investigation of the difference in measured intelligence between twins and single births. Ann Hum Genet 1970;34: 11-20.
Byrns R, Healy J. The intelligence of twins. J Genet Psychol 1936;49: 474-8. "