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The Seashore Measures of Musical Talent tests of Pitch, Loudness, Rhythm, Time and Tonal Memory were administered to these twins, always testing both cotwins simultaneously. For each of the above five tests the heritability, i. e. the intra- pair variability portion that might be attributed to genetic factors, was estimated by comparing the variability within monozygotic twin pairs to the variability found within like-sexed dizygotic twin pairs. Statistically significant genetic components were indicated for pitch discrimination, time discrimination, and tonal memory, as measured by the Seashore Measures of Musical Talent. ii THE HERITABILITY OF SOME MUSICAL APTITUDES by Raymond S. Corwin A Thesis Submitted to the College of Science and Arts Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology East Lansing, Michigan 1960 TABLE OF CONTENTS Introduction Musical Aptitudes The Study Sample Statistical Analysis Data Discussion Summary Acknowledgments Bibliography Appendix Data On Dizygotic Twins Data On Monozygotic Twins Analysis Of Data Computations iv 11 12 13 15 16 17 18 19 THE HERITABILITY OF SOME MUSICAL APTITUDES Raymond S. Corwin INTRODUC TION The study of the genetic factors involved in musical aptitudes is important to a number of fields. First, musical aptitudes, the potentials for musical achievement, offer a group of quantitative characters that are common to all people. Secondly, it may shed some light on an age old question of music education, "Can any person become an accomplished musician provided he receives the necessary training? ”. In other words, are all people genetically alike in their potentialities for musical development? Musical ability, i. e. , musical achievement, has been studied by a number of investigators (Hurst 1908, Drinkwater 1916, Davenport and Seashore 1920, Stanton 1922, Seashore 1923, Mjo'en 1925, Northrop 1931, Reser 1934, Rittershaus 1935, Schank 1936, Scheinfeld 1939). However, several of these studies have suffered serious bias in that the families studied were selected because they had produced large numbers of accomplished musicians. Moreover, the design of these studies did not permit separation of the genetic from the environmental factors in musical achievement. It should be mentioned that most of these studies antedate both objective tests of musical capacity and the methodological advances of modern human genetics. With due con- sideration to the above, the results of these studies can still be said to suggest that heredity may influence the expression of. musical achievement. It is the purpose of this study to estimate the genetic components of certain musical aptitudes by comparing the within-pair variability “of aptitude test scores in monozygotic and like-sexed dizygotic twins using Holzinger's (1929) method of analysis. The musical. aptitudes studied were selected from the six tests comprising the Seashore Measures of Musical Talent. MUSICAL APTITUDES We define a musical aptitude as a psychological character which indicates an individual's potential musical capacity. The Seashore Measures of Musical Talent Were used in this study to measure the following five musical aptitudes: pitch, loudness, rhythm, time and tonal memory. The selection of these tests was based on several considerations. Ideally, a test suitable to our purposes should not measure the effects of either intelligence or musical training, and it should give consistent results when repeated. The reliabilities of The Seashore Measures of Musical Talents were estimated by the Test Division Staff of The Psychological Corporation (1956). Most of the unreliability of the test battery has been attributed to the low reliability of the Timbre test (Mc Leish, 1950). Accordingly we have elected not to use the Timbre test in this study. The five Seashore Measures of Musical Talent qualified more fully than the other tests available. The Kwalwasser-Dykema tests correlate highly with I. Q. (Kwalwasser, 1955), while both the Oregon Test of Musical Discrimination and the Wing Test of Musical Intelligence are probably less Specific than the Seashore tests (Mc Leish, 19 50). The tests for pitch, loudness, rhythm and time are of similar construction. For example, the Pitch Test presents 50 pairs of tones to the subject. The subject must determine, for each pair, whether the pitch of the second tone is higher or lower than that of the first tone. The pitch difference between the tones of each pair decreases progressively. Similarly the abilities to discriminate differences in loudness, differences in rhythmic patterns and in notes held for differing lengths of time are tested. The Tonal Memory test consists of two sequences of notes in which one note in the second sequence differs in pitch from its positional correSpondent in the first sequence. The subject must tell the position in the sequence of the changed note. The length of sequences increases from 3 to 5 notes as the test pro- gresses. For a more detailed description of the Seashore Measures, the reader is referred to the Revised Manual for The Seashore Measures of Musical Talent (1956). Two other similar twin studies have been done with musical aptitudes, one by C. A. Mizer (1941), and another, not yet published, by S. G. Vandenburg. Mizer used the Kwalwasser-Dykema tests, which, as was pointed out earlier, correlate with intelligence. Moreover, Mizer' s method of correlating only aptitude with achievement gave little information on heritability. THE STUDY SAMPLE Twins were drawn from three sources in a haphazard fashion. The first group of 12 monozygous and 6 dizygous twin pairs was obtained by an "I. B. M. sort” from the Michigan State University student body. None of the twins identified through this procedure refused to cooperate though some pairs were excluded because both members could not be present for simultaneous testing. The second group was collected from some of the Lansing, Michigan, public high schools. Three twin pairs were not willing to cooperate. How- ever, 8 monozygotic and 12 dizygotic twin pairs were collected. The third group consisted of 9 monozygotic and 6 dizygotic twin pairs that responded to our request during the 1958 Convention of the International twins Association, held in Detroit, Michigan. The zygosity of the twins was primarily determined from their blood types, employing the ABO, Rh, Lutheran a, MN, P, Kidd a, Kell and Duffy a antisera. Twins were classified monozygotic if they were concordant for all of the blood groups examined and if there were no gross morphological differences between them; otherwise they were classified dizygotic. Three pair whose zygosity was ques- tionable were excluded from the study. STATISTICAL ANALYSIS Holzinger's method of estimating heritability assumes that the variance within like-sexed dizygotic twins, 01%, contains two additive components, one, 0'33, due to environmental factors and the other, 0'2, due to genetic factors. Thus, 0'1?) = (I: + 0'; . However, the variance Within monozygotic co—twms, O'M, contains only the single component, 0123 . That is, 0'12VI 0% . Assuming that (7% is the same for monozygotic as for like-sexed dizygotic twins, (I: can be estimated from the relation 0'3} = 012)- 0.12% = (0-3} + (7%)) - 01%: . For any given trait the proportion of the total variance within dizygotic twins that is attributable to genetic factors is called the heritability ofthat trait. It is defined as 2 2 2 GD_ UM = ”G 0’12) (7&4— (7%; and is estimated by the statistic 2 2 2 SD‘SM h '——'2"~“"’- SD The significance of the difference between h2 and zero is tested by comparing the variance ratio sf) /812VI with unity, using the standard F table with as many degrees of freedom in the numerator and denom- inator as there are pairs of dizygotic and monozygotic twins, respectively. In using the above method it is desirable that the testing environment be as constant as possible. This was accomplished by carefully standardizing the administration of the tests and the preparation of the subjects and by always testing co-twins simultaneously. The same phonograph was used for all tests, using constant volume and tone control settings. The co—twins were always seated at approxi- mately the same distance from the phonograph (80 inches - speaker to table edge). DATA The-sample variances 8% and 52M as well as h:2 were computed for each of the five Seashore Measures of Musical Talent and are shown in Table I. (See Appendix, Tables 1 and 2, and p. 18 for raw data and computations.) The F ratios used to test the significance of the difference between h2 and zero are also shown in Table I with signif— icance indicated at the 1% and 5% levels. (See Appendix p. 18 and Table 3 for computations. ) As may be seen from Table I, h2 was not significantly different from zero for either loudness or rhythm. However, for pitch and time, 2 h was significantly greater than zero at the 5% level, and for tonal memory it was significant at the 1% level. Table I. Within P ir Variances (52), Estimates of Heritability (h ) and F Tests Computed From Seashore Test Scores of 24 Dizygotic (D) and 29 Monozygotic (M) Twin Pairs i 2 2 2 Test SD sM h F Pitch 38. 00 17.08 . 0.55 2. 22* Loudness 14. 00 36. 76 ': -1. 52 0.38 i 3 a Rhythm 4. 56 4. 55 i 0.00 1.00 1 l 1 Time 27.10 13.36 ! 0.51 2. 03* Tonal 18. 25 7.14 0.61 2. 56>:==:= Memory * Significant at the 5 per cent level. ’1‘ *Significant at the l per cent level. DISCUSSION The fact that h2 is not significantly different from zero for Loudness and Rhythm suggests that genetic influences are responsible for little or none of the variability in Loudness and Rhythm scores within dizygotic twin pairs. Thus, it would appear that little information about an individual's inherent musical potentialities can be gained from Seashore's tests of loudness sensitivity and rhythm discrimi- nation. A sense of rhythm has been said to be one of the least essential items to musicians of exceptional talent. These musicians often develop the particular rhythm necessary to portray their own interpretations. (Scheinfeld, 1939). Educators in the music fields would not, then, want to depend on the senses of loudness and rhythm as measured by the Seashore tests in estimating the potentiality of a student, unless they are willing to accept these as indicative of mostly environmentally conditioned qualities. Similarly, it would appear that human geneticists would derive little benefit from further family pedigree studies of these two characters. This conclusion is, of course, based only on negative evidence. Confirmation by another twin study and possibly by results obtained from pedigree studies would strengthen this con— clusion. The h2 values for Pitch, Time, and Tonal Memory indicate the influence of genetic components. Pitch showed a heritability of 0. 55 with an F of 2. 22, significant at the 2. 5% level. This would mean 55 per cent of the variability found within fraternal twins can be attributed to genetic components. Time exhibited a heritability of 0. 51 with an F of 2. 03, significant at the 5 per cent level. Tonal Memory gave a heritability of O. 61 with an F of 2. 56, significant at the 1 per cent level. Interesting pedigree studies might now be done on these three characters. Also, based on this evidence, it would not be surprising to find musical training less effective in overcoming deficiencies in pitch discrimination, time discrimination, and tonal memory than in loudness and rhythm discrimination. Although many controls were exercised, variability has entered the study both through sampling errors in the selection of twins and through the testing procedures. Much of this variability would tend to make the computed h2's underestimates of the true heritabilities. It has been suggested that the prenatal environment of fraternal twins is much more similar than that of identical twins (Price 19 50). Price feels that identical twins, in unequally sharing the same blood supply, usually have dissimilar uterine nourishment, growth, and birth weight. Fraternal twins, who do not compete for uterine blood supply, gener- ally are more alike in prenatal growth and neonatal weight. This phe— nomenon might tend to spuriously diminish estimates of heritability by increasing the intra-pair variance in monozygotic twins. However, other studies not yet published may fail to confirm Price's hypothesis. Also, the postnatal environments are thought to be more similar for 10 identical than for fraternal twins, tending to exaggerate estimates of heritability obtained in this way. It was not possible to control or measure a number of variables, e. g. subject's emotional maturity, and variations in the reproduction of test sounds. We assume, however, that the extent of these variables in the monozygotic twin sample is approximately equal to that in the dizygotic twin sample and consequently that little or no bias results from them. It might be worthwhile to make two improvements in future studies of this type, using these tests. As Mc Leish (1950) has sug— gested, a slower presentation of the individual test items would be advantageous. Secondly, the relatively low reliability coefficients indicated in the Manual for the Seashore Measures of Musical Talent (1956) suggest that it would be desirable to retest in each case. 11 SUMMARY Five of the Seashore Measures of Musical Talent; Pitch, Loudness, Rhythm, Time and Tonal Memory, were used to test the musical aptitudes of 29 pairs of monozygotic twins and 24 pairs of like-sexed dizygotic twins. The proportion, h2, of the variance within pairs of like-sexed dizygous twins which is attributable to genetic factors, was estimated by Holzinger's twin study method. Data collected in the present study suggest that genetic factors account for a statistically significant proportion of the variability in pitch, time, and tonal memory within dizygotic twin pairs. However, the h2's for loudness and rhythm were not significantly different from zero, suggesting that variation in these traits may be largely attributable to the environment. These results lay the ground work for pedigree studies of pitch, time and tonal memory, or additional twin studies of musical aptitude. 12 ACKNOWLEDGMENTS I wish to thank the twins that participated in this experiment for their wonderful cooperation. I am indebted to both the Lansing, Michigan School System and the International Twin Association for their assistance in securing twins. I wish to express my deepest appreciation to Dr. Harold O. Goodman of Bowman Gray School of Medicine, Department of Human Genetics for his stimulating guidance, counsel, and encouragement throughout the study, and to Drs. Philip J. Clark and Karl A. Stiles of Michigan State University, Department of Zoology for their repeated critical reading. 13 BIBLIOGRAPHY Bienstock, S. F. 1942. A review of recent studies on musical aptitude. J. Educ. Psychol. 33:427-442. Davenport, C. B. 1911. Heredity ERelation To Eugenics. New York, N. Y. Henry Holt and Co. Drinkwater, H. 1916. Inheritance of artistic and musical ability. J. Genet. 5:229—241. Gates, R. R. 1946. Human Genetics. New York, N. Y. The Macmillan Co. Holzinger, K. J. 1929. The relative effect of nature and nurture influences on twin differences. J. Educ. Psychol. 20:241-48. Hurst, C. C. 1908. Mendel's Law of Heredity and its Application to Man. Leicester Lit. Phil. Soc. Trans. 12:35. Kwalwasser, J. 1955. Exploring The Musical Mind. New York, N. Y. Coleman-Ross Co. Inc. Mc Leish, J. 1950. The validation of Seashore's Measures of Musical Talent by factorial methods. Brit. J. Psychol. 32129-40. Mizer, C. A. 1941. Correlation of Scores Earned by 25 Pairs of Twins in Music Talent and Music Achievement Tests. Thesis, Syracuse University. deen, J. A. and F. 1925. Zur Erbanaluze der musikalischen Begabung. Hereditas. 72109-28. Price, B. 1950. Primary biases in twin studies. Amer. J. Human Genet. 2: 29 3-352. PaychologiC-al Corporation, Test Division Staff. 1956. Revised Manual for Seashore Measures of Musical Talents. New York, N. Y. The Psychological Corporation. Reser, J. 1934. Inheritance of musical ability. Eugen. New. 20:8—9. Rittershaus, E. 1935. Die Vererbung musikalischer Eigenschaften. Arch. f. Rass. Biol. 29:132-52. Schank, A. 1936. The inheritance through six generations of pro- nounced musical ability. Eugen. News. 21:14-16. Scheinfeld, A. 1939. You And Heredity. New York, N. Y. Frederick A. Stokes Co. Seashore, C. E., Lewis, C.. and Saetveit, J. G. 1940. Revision of the Seashore Measures of Musical Talents. Univ. Ia. Studies, N. 65. Stanton, H. M., and Koerth W. 1933. Musical Capacity Measures of Children Repeated After Musical Training. Univ. of Ia. Studies, No. 42. Stanton, H. M. 1935. Measurement of Musical Talent, The Eastman Experiment. Studies in the Psychology of Music Vol. II. Univ. of Ia. Studies. 15 BI?! II... .8 V In! “It: I'll, ’J‘WL! I ‘— APPENDIX Table 1 . Data On Dizygotic Twins. Test Scores (number wrong) Twin Age Sex Pair (years) (M Pitch 21%? Rhythm Time M12331), No. or F) twin twin twin twin twin a b a b a b a b a b 1 20 F 5 5 3 6 5 2 2 5 5 13 2 22 F 2 14 4 4 0 1 14 7 O 2 3 21 F 5 3 5 4 3 4 8 4 1 0 4 20 F 12 9 8 7 4 3 14 6 3 12 5 22 M 10 6 6 5 3 2 7 10 0 1 6 19 F 6 6 7 7 8 3 13 10 8 5 7 17 F 26 19 5 8 5 6 10 13 19 10 8 17 F 5 6 11 6 4 1 12 18 6 4 9 16 F 15 6 4 3 3 7 14 12 13 10 18 F 9 25 16 17 6 11 14 9 9 19 11 18 F 9 3 11 5 3 4 19 10 11 8 12 17 M 4 19 11 6 2 4 18 7 19 13 13 19 F 5 8 6 2 6 13 22 1 2 14 16 M 15 31 6 15 3 7 6 22 3 13 15 19 F 8 11 6 5 6 6 20 9 4 6 16 18 F 20 12 9 7 6 5 9 18 13 11 17 16 F 26 14 4 12 5 7 17 11 11 8 18 18 M 12 21 8 11 9 3 17 10 16 13 19 19 M 6 12 3 4 1 2 5 11 1 7 20 12 F 32 22 9 23 10 16 14 26 16 22 21 12 F 8 8 5 13 6 11 14 6 1 22 15 M 24 12 18 6 7 5 21 16 26 15 23 14 F 18 29 13 21 11 8 18 16 8 18 24 24 F 7 7 7 7 2 1 8 14 6 2 l6 Table 2 . Data On Monozygotic Twins Test Scores (number wrong) Twin Age Sex Pair (years) ‘ (M Pitch Loud- Rhythm Time Tonal No. or ness Memory F) twin twin twin twin twin a b a b a b a b a b 1 20 F 13 4 9 9 1 1 9 5 3 1 2 21 M 6 4 10 9 6 5 9 9 4 4 3 18 F 3 3 11 9 5 4 8 9 4 4 4 19 M 2 2 4 5 6 1 3 5 0 1 5 19 F 10 9 7 8 3 2 ll 5 2 2 6 19 F 13 V 10 10 4 2 l 9 10 2 5 7 19 M .1 3 6 2 3 5 6 3 5 5 8 20 F 2 l 5 9 1 l 8 8 0 0 9 24 M 13 19 6 6 4 3 6 10 8 6 10 19 M. 3 10 6 8 1 5 4 9 3 2 11 22 F g 6 7 8 6 1 1 9 3 2 0 12 22 Mi37 19 5 3 8 5 8 5 15 19 13 19 F1 4 8 8 4 4 1 13 14 1 0 14 15 F ; 4 - 14 ‘ 9 7 5 8 12 11 11 10 15 39 F [27 24 15 12 9 10 6 10 12 16 16 16 M 10 12 8 5 10 6 15 l4 l7 5 17 16 M 20 17 11 8 6 2 16 10 5 7 18 18 M 24 19 24 8 5 2 23 23- 15 18 19 26 M 10 6 16 6 4 8 7 10 9 5 20 15 F 26 25 8 7 8 12 17 10 18 16 21 39 F 13 28 12 29 8 6 19 25 9 9 22 31 F 21 19 15 13 10 8 10 10 13 14 23 36 M 5 5 7 2 5 4 10 9 8 4 24 42 F 28 28 25 35 10 14 31 17 9 15 25 19 F 3 9 2 5 4 10 9 7 7 14 26 25 F 18 18 33 8 9 8 17 13 19 1:5" 27 10 M 22 28 29 32 5 10 27 27 14 15 28 25 F 18 15 40 16 17 12 16 32 22 16 29 28 M21 21 16 14 7 8 15 15 22 17 .. u m. -fi l8 ANALYSIS OF DA TA The formula for the variance within twin pairs is k 2 2 2 2: z X.. 2 _ i=1 3-1 11 1 j-l ii 2 k where Xij is the score made by the jth individual of the 1th twin pair and k is the number of twin pairs in the sample. The variance within monozygotic twin pairs is designated by 812VI and that within dizygotic pairs by SE) . 19 Table 3 . Computations . Pitch Loudness Rhythm Time Tonal Mem. For DZ 2 X 594. 0 385. 0 235.0 597. 0 418. 0 z X2 10585. 0 4258. 0 1509. 0 8893. 0 5535. 0 Z T2 19348.0 7784. 0 2999. 0 16485. 0 10395. 0 4 2 9574. 0 3892.0 1499. 5 8242. 5 5198. 0 Sum qu. 912. 0 355. 0 109. 5 550. 5 438. 0 sg (+24) 38.0 14.0 4. 55 27.1 18.2 For MZ z X 773. 0 554. 0 330. 0 591. 0 504. 0 2x2 14995. 0 11802. 0 2550. 0 10891. 0 5788. 0 2T2 28999. 0 21472. 0 5035. 0 21007. 0 13152. 0 + 2 14499. 5 10735. 0 2518. 0 10503. 5 5581. 0 Sum qu. 495. 5 1055. 0 132. 0 387. 5 207. 0 Si, (+29) 17.1 35. 8 4. 55 13.4 7.14 h2 0. 550 -1. 525 0.002 0.507 0. 509 F24, 29 2. 224. ' 0. 381 1. 002 2. 028 2. 557 Sifiiiél 2. 5% - - 5. 0% 1. 0% F. 05 F 01(24, 29) - 2.49 (24, 29) - 1. 90 MGM USE ONLY 3 .117” “fluiv {13" hi" "us-’6 L 5): (:5 ‘5. 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