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Similarities in grip strength, and tests of running, jumping and throwing performance are considered in 198 sibling pairs, 6 through 13 years of age, living under conditions of chronic mild-to-moderate undemutrition in rural, southern Mexico. All correlations are quite low. Sisters tend to resemble each other more than brothers in the motor performance tasks, while there is no consistent pattern of sex differences in right and lift grip strength. Controlling for the effects of body size does not significantly affect the sibling correlations. Brother-brother correlations for grip strength de­crease, while sister-sister correlations increase. In contrast, sibling correla­tions for running, jumping and throwing change only slightly when body size is controlled. Sibling correlations for the same tasks tend to be higher in well-nourished children. However, sisters resemble each other more than brothers in the undernourished sample, while brothers are more similar than sisters in the better nourished sample.


There was a minor omission in the report. The sibling correlations for the total sample in Table 2 (p. 948) were omitted in setting. The correlations are as follows: Right grip .17 Left grip .13 Dash .17 Jump .03 Throw -.05 In addition, the name of Sklad is misspelled (p. 945 & 953). The Polish letter ‘Ɨ” with a slash through it was mistaken as a “t” in typesetting.