Australian Journal of Basic and Applied Sciences, 5(6): 1517-1524, 2011 ISSN 1991-8178

The Correlation Between Left-sidedness and Intelligence as an Advantage for Persistence of Left-handed Frequency in Human Evolutionary Pathway

1Hengameh Alibeik, 2S. Abdolhamid Angaji, 2Sara Pouriamanesh, 3Gita Movallali

1Department of Biology, North Tehran Branch, Islamic Azad University, Tehran, Iran. 2Department of Biology, Tarbiat Moallem University, Tehran, Iran. 3Department of Psychology and Education of Exceptional Children Group, University of Social Welfare, Rehabilitation Sciences (USWR), Tehran, Iran.

Abstract: Hand preference is the most studied form of lateralization. Left-handers have coexisted with right- handers at least since the Upper Paleolithic and left-handers are in the minority in all human populations. Handedness is not neutral and some costs are associated with left handedness. The most frequency cited costs are a reduced longevity, a smaller height and weight, late puberty and a larger developmental instability. The persistence of the polymorphism of handedness is interesting and suggests that left-handedness must be associated with some benefits. In humans has been proposed that it is maintained by negative frequency-dependent selection. In this study, the relationship between psychological and motor systems was investigated and the correlation between handedness, eyedness, footedness and combination of them with intelligence were determined. Nonverbal intelligence was assed using the Persian transltion of WAIS-R. T-test was applied for comparison between groups; the results indicated that those use right hand and right eye and individual with left hand and right eye have much higher creativity in comparison with others.

Key words: laterality, intelligence, crossed dominance

INTRODUCTION

Handedness is a polymorphic trait in humans. In western societies today, about 90% of the adult population is said to be right-handed, with the remaining 10% consisting of persons variably identified as left- handed, ambidextrous, and/or ambiguously handed (McManus, C., 2002; Soper et al., 1986; Ferrari. M., 2007). The same polymorphism is found for other lateral preferences, like eyedness and footedness (Porac and Coren, 1981). Hand preference has been shown in many studies to run in families, the offspring of two left handed parents, being more likely to be left handed than the offspring of two right-handed parents, (Annett, M.,1985; McManus, I.C., 1991; Alibeik, H., Angaji, S.A., 2010a). Similarly, there are data in the literature suggesting that eyedness runs in families (Zoccolotti, P., 1978) and that footedness shows familial trends (Porac and Coren, 1981). People who do not have a dominant hand are said to be crossed dominant. Crossed dominance also refers to a condition where the person's dominant eye, ear, foot, or hand is not on the same side. The figures imply that at least 20% of the population will prefer to use one hand and the other eye. Many theorists, particularly in the area of education, have focused on this phenomenon (Bourassa et al., 1996). Hand preference is the most studied form of lateralization. Left-handers have coexisted with right- handers at least since the Upper Paleolithic and left-handers are in the minority in all human populations. Handedness is not neutral (Faurie, C., M. Raymond,2003; Faurie,C., M. Raymond, 2005; Alibeik, H., Angaji, S.A., 2010b) and some costs are associated with left handedness. The most frequency cited costs are a reduced longevity, a smaller height and weight, late puberty and a larger developmental instability (Aggleton et al., 1993; Coren and Halpern, 1991; Gangestad and Yeo, 1997; Faurie et al., 2006). The persistence of the polymorphism of handedness is interesting and suggests that left-handedness must be associated with some benefits. In humans has been proposed that it is maintained by negative frequency-dependent selection (advantage being greater when the frequency of a trait is lower) (Billiard et al., 2005; Llaurens et al., 2009). The frequency-dependent advantage of left-handers in physical fights is strongly suggested by both the study of interactive sports in industrialized societies and a cross-cultural comparison of traditional societies. In western societies, Left-handers are supposed to have a socio-economic status advantage. Differences in brain organization have been observed

Corresponding Author: S. Abdolhamid Angaji, Department of Biology, Islamic Azad University, North Tehran Branch, Iran. E-mail: [email protected] 1517 Aust. J. Basic & Appl. Sci., 5(6): 1517-1524, 2011

between left- and right-handers. Brain structures and functions are certainly linked to social and intellectual skills, on which socio-economic status depends (Faurie et al., 2008). Left-handed people are seen to be more creative, more likely to notice the size, shape and form of things, more likely to see the whole picture or concept. It has been proposed that perception has direct relationship with the intelligence of a person and studies have indicated that perceptual power of left-handers is more specialized than that of right-handers because of the dominance of right hemisphere (Ghayas and Adil, 2007). The aim of this study is to identify the evolutionary forces involved on human handedness respectively sidedness. To that, the relationship between psychological and motor systems were investigated and tried to determine the correlation between hemispheric laterality and side preference to nonverbal intelligence. It was proposed left handed persons or those with a preference at the left side of their body depend on their distinct organization of the brain, have better perceptual power and socio-economic status advantage. The good fitness and significantly advantage possibly helped them to persist since thousands of years. To improve our understanding of above explained proposal, the following items were studied and measured: 1. the nonverbal intelligence of left hander, left eyed and left footed individuals compared to right hander, right eyed and right footed persons as single-organ groups, 2. The nonverbal intelligence of groups of persons who showed 'crossed’ lateral preferences (right-handed, left-footed and left-eyed; left-handed, right-footed and right-eyed; left-handed, left –footed and right-eyed etc.) or ‘uncrossed’ lateral preferences (right-handed, right-footed and right -eyed or left-handed, left-footed and left-eyed) as multi-organ groups, and lastly compared them together. Finally, it was tried to determine the influence of sex on given results. To our knowledge, data on both nonverbal intelligence and handedness are available in the literature. Some studies found that left-handers have lower intellectual performance, while others found no differences between right and left-handers and an advantage for left-handers was observed in some studies (Resch et al., 1997; Johnson, 0., C. Harley, 1980; Bradshaw et al., 1981; Tan.U., 1998; Faurie et al., 2008). In this research, we studied not only the relationship between hand preference and intelligence, but also this data set was extended to other side preferences. In line with the above mentioned cases, hand preference was assessed by the Edinburgh Handedness Inventory, and a laterality score (Geschwind score) was calculated for each subject. Laterality for eyedness and footedness was evaluated using 3 markers for each one. Nonverbal intelligence (spatial reasoning) was appraised by using the Persian translation of the WAIS-R (Wechsler, 1981), Which is the most widely used intelligence test for adults in Iran and has also been found to be a good measure of fluid and crystallized intelligence. In the WAIS, fluid intelligence is reflected in the performance subtests (Cattell, R.B., 1963; Groth-Marnat, G,. 1997; McGrew et al., 1989; Kline, 2000; Wechsler, 1981; Kaufman and Lichtenberger, 2002).

MATERIAL AND METHODS

The subjects were 86 students (78 female and 8 male) from Azad University Tehran (north branch) and Tarbiat Moalem University who voluntarily participate in the study. They ranged in age from 20 to 26years. The subjects were healthy, devoid of neurological or psychiatric signs, and symptoms.

Side Preference Assessment: To assess the hand preference, the subjects received a Persian translation of the Edinburgh Handedness Questionnaire (Oldfield, 1971). It consists of 20 items describing different hand motor activities. On the response sheet, each item was followed by two columns labelled left and right. Every subject was requierd to mark a "+" in the appropriate column if the activity was preferentially carried out using one hand, a "++" if no way the other hand would be used unless in a forced situation, and "+" in both columns in case of real indifferences on which hand to use. A laterality score was calculated (Geschwind score, GS) instead of a laterality quotient. GS of - 100 indicated that the subject responded “always left.” The GS of +100 indicated always right on all items. Eyedness was assessted by 3 items: Eye used for looking into a dark bottle, Eye used for looking through a hole and Eye used for looking through a camera lens. Footedness was appraised by 3 items: Kicking a ball, picking up a pebble and stepping onto a chair.

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Intelligence Assessment: The intelligence profile was assessed using the Persian translation of the WAIS-R (Wechsler, 1981), which is the most widely used intelligence test for adults in Iran. All testing was done on an individual basis. The WAIS-R was administered and scored according to the instructions in the manual (Wechsler, 1981). Nonverbal IQ (performance IQ) was evaluated by a psychologist using 6 subtests including picture completion, picture arrangement, block design, digits symbol and object assembly. The raw scores were converted into intelligence quotients (IQ), according to the table for converting raw scores directly into IQs. Finally Data analysis including t-test for mean comparison and F-test for variance comparison were carried out using Data SPSS 16 and SASS 9.1 on a computer.

RESULTS AND DISCUSSION

Initially, the nonverbal of 86 students were assessed and classified into six classes with forth class having the highest frequency (Figure 1). The overall mean was around 106.8, with a standard deviation about 11.3 using SAS (version 9.1) software. The character seems to vary continuously among students and the distribution of the trait cannot be distinct into discrete phenotypic classes, suggesting that the trait is polygenic or quantitatively inherited. In Fig. 1, elongated tail is at the left side of the graph and more data is in the left tail than would be expected in a normal distribution, i.e. the data is negatively skewed, with skewness value of around -0.03 which is considered slightly skewed since it is between 0 to -0.5.

Fig. 1: Frequency of nonverbal intelligence for 86 students ranged in age from 20 to 26 years.

Group Comparisons: Comparison Based on Two Organs: In order to find significant difference among the subjects, the population was divided into 12 groups based on two of three organs including hand, foot and eye. The significant results (Table 1, 2 and 3) at 5 percent are as follows:

Table 1: Mean and t test of nonverbal intelligence between those with right preference for hand and eye and the subjects with left preference for the two organs. Eyedness and Handedness N Mean t Right hand & Right eye 29 2.163* 109.72 Left hand & Left eye 22 103.31 df= 49, * p< .05

Table 2: Mean and t test of nonverbal intelligence between the left handed and right eyed students and those with right preference for the two organs. Eyedness and Handedness N Mean t Left hand & Right eye 11 2.320* 112.27 Right hand & Right eye 29 109.72 df= 38, * p< .05

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Table 3: Mean and t test of nonverbal intelligence between those who prefer right side for eye and foot with the right eyed and left footed students. Eyedness and Footedness N Mean t Right eye & Right foot 30 2.356* 109.76 Right eye & Left foot 6 100.16 df=34, *p< .05.

Comparison Based on Three Organs: To look for significant difference among the students, they were classified into eight groups based on three organs including hand, foot and eye. The significant results (Table 4 and 5) at 5 percent are as follows:

Table 4: Mean and t test of nonverbal intelligence between those who prefer right side for the three organs with the right handed, right footed and left eyed students. Eyedness and Handedness&Footedness N Mean t Right hand &right eye& right foot 27 2.103* 109.92 Right hand &Right foot & left eye 11 102.54 df= 36, p< .05

Table 5: Mean and t test of nonverbal intelligence between those left eyed who prefer right side for the hand and foot with the left- handed, left-footed and right eyed students. Eyedness and Handedness&Footedness N Mean t Left hand & Left foot & Right eye 7 2.08* 111.14 Right hand &Right foot& left eye 11 102.54 df=16, p < .05

Discussion: The present study is mainly concerns psychomotor relationships and tries to answer two questions: Is there an association between side preference of motor organs like hand, eye and foot with intelligence of individuals? Is the IQ rate of people who combine a variety of preferences different? Moreover, it was tried to answer the question whether the correlation between left-sidedness and intelligence can be considered as an advantageous factor for persistence of left-sided frequency in human evolutionary pathway. To assess mental ability, the Persian translation of WAIS-R (Wechsler, 1981), which is the most widely used intelligence test for adults in Iran, was used. WAIS-R gives a global IQ and also two separate IQ’s for the two scales: verbal and performance (nonverbal). Since left-handedness is considered to be associated with right-hemisphere activities and functions, we evaluated only those rated that were related to non-verbal intelligence. The results of IQ changes in society revealed the presence of coherence and also indicated a quantitative trait under multiple gene inheritance control which is supported by other studies as well (McManus, 2002; Francks et al., 2003). The results derived from two-organ comparisons showed a significant difference for two organs; hand and eye. Right handed and right eyed people were more creative than left handed and left eyed people. The results also indicated higher scores for individuals with a right side preference compared to those with a left side preference. It was also found significant differences between participants who preferred right side of their bodies compared to those with mix preferences between which left handedness -right eyedness combination exhibited the highest points. Comparisons of three-organ groups also showed people with right preferences had higher non-verbal IQ than those who preferred to utilize the left side of their bodies. However, the individuals who were left sided for hand and foot but were right eyed, exhibited the highest scores compared to those who were right sided or had other mix preferences. Since left footed- right eyed individuals had lower scores than left handed- right eyed persons, it seems that only left hand - right eye combination is suitable and their carriers can be introduced as the most creative people. Data analysis in all groups showed a score superiority for individuals with a right side preference in comparison to those who preferred the left side of their bodies. However we assumed the nonverbal intelligence and spatial power of left sided participants must be more than those with right side preference. Such results had already been reported in previous studies of scientists. The explanation for this deficit has

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been dubbed the "cognitive crowding hypothesis", the term implying that spatial ability has been compromised (partly "crowded out") by the relatively greater degree of commitment of right hemisphere neural networks to language (Milner, 1974; Sperry, 1974; Teuber, 1974). Nettle et al. (2003) found that extreme right-handers have minimal variance in IQ and left-handers have a large variance (p<.001). The major factors that can be involved in this variance are sex, familiar sinistrality (+FS), patterns of cerebral lateralization and different levels of reasoning ability, and outcome of their interaction could result a special and unique phenotype (Nettle, 2003). The present study was able to show the correlation between variety of people with different left side preferences and nonverbal IQ which itself is related to a degree of cerebral lateralization. On the other hand, inter-sex comparisons exhibited superior scores for strong left sided males and inferior scores for strong left handed female. These findings were consistent with studies of Tan, (1989). On average, 10% of people in the world are left-handed, 30% are left eyed and 20% are left footed. All paired muscle systems are represented in the brain by paired controlling centers. Dominance, or leading control of the function, may be entirely left sided, in which case the organs controlled are dominant on the right side, or entirely right-sided. If some centers are on the left and some on the right side of the brain, the condition is called "crossed laterality". At least 20% of the population exhibits a crossed dominance. Johnson and Harley, (1980), found, that strong left-handers of both sexes obtained higher verbal scores but lower spatial scores than did right- or mixed-handers. In contrast to the above findings, Tan, (1988), using Cattel's Culture Fair Intelligence test (primarily a measure of nonverbal reasoning ability), observed moderate left-handedness to be associated with the highest scores. Also, Sanders and coworkers, (1982), found that in three ethnic groups, strongly left-handed males had higher spatial scores than the strongly right-handed males, while the opposite pattern was found for females. In addition, among those individuals of Chinese or Japanese (but not European) ancestry, strongly left-handed subjects had higher spatial scores than both right-handed and ambidextrous subjects. Schwartz, (1988) found that left-handed, left-eyed females (who may have a higher incidence of FS+ in general) exhibited a better performance than right-handed, left-eyed females. Kocel, (1977) observed FS + to be related to higher spatial scores in females and lower spatial scores in males. The data analysis in our study indicated that mix preference can be associated with high nonverbal scores, especially when the left hand preference was in corporation with right eyedness, Eyedness is one of the consequences of brain lateralization. Like Handedness, a number of studies exhibit evidences that eyedness could run in families and that a broadly similar genetic model may be responsible for its appearance. However if there is an association between handedness and eyedness then it must result either from pleiotropy of a single genetic system, or epistatic interactions between two or more genetic systems (Bourassa et al., 1996). Eyedness is related to handedness, which itself is also associated with cerebral lateralization of language. Although manifest handedness may be altered by training, no attempts are made to change the sighting eye. Many authors (Delacato, C.H., 1959; 1963; 1996; O' Connor, 1965) have considered eyedness as a more fundamental measure of an underlying laterality since it is not altered by influences of cultural pressures. Most people present coordination between handedness and eyedness. Subsequently, Delacato (1959,1963,1966) suggested that consistent handedness and eyedness (and footedness) is necessary for normal intellectual development, particularly of reading and speech. Despite the fact that large-scale surveys have shown no association between crossed laterality and intellectual abilities (McManus and Mascie-Taylor, 1983), such theories continue to be influential. In this study some novel aspects of crossed laterality was observed, which may not lead to disorders, but also might cause high cognitive abilities and amazing imaginations. After we evaluated the correlation between left sidedness and Intelligence as positive (at least in one group of participants with a left hand - right eye preference),the second part of our discussion is dedicated to explain how can this advantage be justified as a factor for persistence of left-sided frequency in human evolutionary pathway. The frequency-dependent advantage of left-handers in physical fights is strongly suggested by both the study of interactive sports in industrialized societies and a cross-cultural comparison of traditional societies. However, in other societies it is unclear how this advantage operates. Moreover, left-handers may have other selective advantages. The high cognitive abilities and superior intelligence of left handed (left sided) people are proposed as socio-economic advantages. According to Faurie, (2008), a socio-economic advantage is necessarily frequency-dependent: the status of an individual is relative to the status of others in his/her social group. Socio-economic status is an important component of the reproductive value in most human societies. One of the main components accounting for the relationship between socio-economic status and hand preference is the existence of possible differences in cognitive abilities of individuals. Having superior intelligence and high creativity lead to career success, more income and better socio economic status that help

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individuals to continued survival and persistence. From evolutionary perspective, if men be able to have unique advantages, could have better success to mate and producing more offspring. Coren, (1995) reported that creativity and novelty to be linked with left- handedness, more specifically in men. Several studies have found lefthanders are more frequent in some professions and some educational fields, such as arts, music, mathematics and architecture. According to Denny & O’Sullivan, (2007), the hourly earnings of left-handed men was greater (approx. 4%) and observed an opposite result for right-handed women. Ruebeck et al. (2007) also found a significant increase of wage for left-handed men in the group with high levels of education and did not observe any effects of handedness on wages for women. The differences between right- and lefthanders socio-economic statuses could be related to their reproductive success, though the importance of socio-economic status in human mate choice directly benefits the offspring. While in the initial part of our discussion, we evaluated the positive relationship between crossed dominance (left handedness-right eyedness) and intelligence as the most appropriate combination, but in terms of gender we reported the strong left handed men as the most intelligence individuals, which is compatible exactly with latter evolutionary analysis. Finally we refer to cases which could be considered in the next researches or could be counted as new research subjects.The sample population size should be larger and comparisons between genders should be done; each of the Wechsler nonverbal subtests needs to be separately analyzed and compared; other intelligence tests like "Raven Standard Progressive Matrices Test (RSPMT) and Cattle Culture Fair" should be used to ensure the results being consonant and the researchers should be informed about participants of being familiar sinistrality positive or negative.

REFERENCES

Alibeik, Hengameh., S. Abdolhamid. Angaji, 2010a.evolutionary back grounds of human left handedness.Research Journal of Biological Sciences, 5(1): 36-41. Alibeik, Hengameh., S. Abdolhamid. Angaji, 2010b. Developmental Aspects of Left-handedness. Australian Journal of Basic and Applied Sciences, 4(5): 877-881. Aggleton, J.P., R.W. Kentridge and N.J. Neave, 1993. Evidence for longevity differences between left handed and right handed men: An archival study of cricketers. J. Epidemiol. Commun. Health, 47: 206-209. Annett, M., 1985. left,right,hand and brain:the right shift theory.london:Erlbaum. Billiard, S., C. Faurie and M .Raymond, 2005. Maintenance of handedness polymorphism in humans: a frequency-dependent selection model.Journal of Theoretical Biology, 235: 85-93. Bourassa, D.C., I.C. McManus and M.P. Bryden, 1996.Handedness and Eye-dominance: A Meta-analysis of Their Relationship. LATERALITY, 1(1) :5-34. Bradshaw, J.L., N.C. Nettleton and M.J. Taylor, 1981. Right hemisphere language and cognitive deficits in sinistrals? .Neuropsyclologia, 19: 113-132. Cattell, R.B., 1963. Theory of fluid and crystallized intelligence: A critical experiment. Journal of Educational Psychology, 54: 1-22. Coren, S., 1995 .Differences in divergent thinking as a function of handedness and sex. Am. J.Psychol., 108: 311-325. Coren, S., D.F. Halpern, 1991. Left-handedness: A marker for decreased survival fitness. Psychol. Bull., 109: 90-106. Delacato, C.H., 1959. Treatment and prevention of reading problems. Springfield, IL: C.C. Thomas. Delacato, C.H., 1963. The diagnosis and treatment of speech and reading problems. Springfield, IL: C.C. Thomas. Delacato, C.H., 1966. Neurological organisation and reading. Springfield, IL: C.C. Thomas. Denny, K., V. O’Sullivan, 2007 .The economic consequences of being left-handed: some sinister results. J. Hum. Resour, 42: 353-374. Ferrari. M., 2007.Cognitive performance and left-handedness: comparative analyses in adults with seizures, physical, psychological and learning disorders in a rehabilitation setting. Journal of Rehabilitation Faurie, C., M. Raymond, 2003. Handedness, Neutral or adaptive?. Behavioral and brain sciences, 26: 220- 220. Faurie, C., M. Raymond, 2005. Handedness, homicide and negative frequency-dependent selection. Proc. R. Soc. B,. 272: 25-28.

1522 Aust. J. Basic & Appl. Sci., 5(6): 1517-1524, 2011

Faurie, C., N. Vianey-liaud and M. Raymond, 2006. Do left-handed children have advantages regarding school performance and leadership skills?. Laterality, 11(1): 57-70. Faurie, C., S. Bonenfant, M. Goldberg, S. Hercberg, M. Zins and M. Raymond, 2008. Socio-economic status and handedness in two large cohorts of French adults. Br. J. Psychol., 99: 533-554. Francks, C., L.E. Delisi, S.E. Fisher, S.H. Laval, J.E. Rue, J.F. Stein and A.P.Monaco, 2003. Confirmatory Evidence for Linkage of relative hand skill to 2p12-q11. American Journal of Human Genetics, 72: 499-502. Gangestad, S.W., R.A. Yeo, 1997. Behavioral genetic variation, adaptation and maladaptation: An evolutionary perspective. Trends Cogn. Sci., 1: 103-108. Ghayas, S., A. Adil, 2007. Effect of handedness on intelligence level of students. J. Indian Acad. Applied Psychol., 33: 85-91. Groth-Marnat, G., 1997. Handbook of Psychological Assessment, 3rd edition. New York: John Wiley and Sons. Johnson, 0., C. Harley, 1980. Handedness and sex differences in cognitive tests of brain laterality. Cotter, 16(1): 73-82. Kaufman, A.S., E.O. Lichtenberger, 2002. Assessing adolescent and adult intelligence (2nd ed.). Boston: Allyn & Bacon. Kline, P., 2000. The Handbook of Psychological Testing. New York: Routledge, pp: 744. Kocel, K.M., 1977. Cognitive Abilities: Handedness, familial sinistrality and sex.ANNALS of the new York academy of sciences, 299: 233-243. Llaurens, V., M. Raymond and C. Faurie, 2009. Why are some people left-handed: An evolutioanry perspective. Phil. Trans. R. Soc. London B., 364: 881-894. McManus, C., 2002. Right hand left hand: The origins of asymmetry in brains, bodies, atoms and cultures. Cambridge, MA: Harvard University Press. McManus, I.C., 1991. The inheritance of left-handedness. Paper presented at the biological asymmetry and handedness ciba foundation symposium, London, 162: 251-267. McGrew, Kevin., Dawn .P. Flanagan, 1998. The Intelligence Test Desk Reference. Needham Heights, MA: Allyn and Bacon. McManus, I.c., C.G.N. Mascie-Taylor, 1983. Biosocial correlates of cognitive abilities. Journal of Biosocial Science, 15: 289-306. Milner, B., 1974. Hemispheric specialization. Neurosciences Third Study Progrant. Cambridge, MA: MIT Press, pp: 75-89 Nettle, D., 2003. Hand laterality and cognitive ability: a multiple regression approach. Brain and Cognition, 52: 390-398. O’Connor, J., 1965. Eyedness and cross-dominance. Boston, MA: Johnson O’ Connor Research Foundation. Oldfield, R.C., 1971. The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychology, 9: 97-113. Porac, C., S. Coren, 1981. lateral preferences and human behavior.new york:springer-verlag. Resch, F., J. Haffner, P. Parzer, U. Pfueller, U. Strehlow and C. Zerahn-Hartung, 1997. Testing the hypothesis of the relationships between laterality and ability according to Annett’s right shift theory: Findings in an epidemiological sample of young adults. British Journal of Psychology, 88: 621-635. Ruebeck, C.S., J. E.Hrington Jr and R. Moffitt, 2007. hndedness and earnings. Laterality, 12: 101-120. Sanders, B., J.R. Wilson and S.G. Vandenberg, 1982. Handedness and spatial ability. Cortex, 18: 79-89. 39. Schwartz, M.,1988. Handedness, prenatal stress and pregnancy complications. Neuropsychologia, 26(6): 925-929. Soper, H.V., P. Satz, D.L. Orsini, R.R. Henry, J.C. Zvi and M. Schulman, 1986. Handedness patterns in autism suggest subtypes. Journal of Autism and Developmental Disorders, 16: 155-167. Sperry, R.W., 1974. Lateral Specialization in the Surgically Separated Hemispheres. The Neurosciences,3rd Study Program, Rockefeller University Press, N.Y, pp: 5. Tan, .U., 1989.Nonverbal Intelligence, Familial Sinistrality and Left-Handedness,Intern. J. Neu roscience, 44: 9-16. Tan, U., 1988.The Relationship Between Nonverbal Intelligence, Familial Sinistrality and Geschwind Scores in Right-Handed Female Subjects.International Journal of Neuroscience, 43(3-4): 177-182. Teuber, H.L., 1974. Why two brains?.the Neurosciences: 3rd Study Program. Cambridge, MA: MIT Press, pp: 71-74.

1523 Aust. J. Basic & Appl. Sci., 5(6): 1517-1524, 2011

Wechsler, D., 1981 .Manual for the Wechsler Adult Intelligence Scale-Revised .New York:Psychological Corporation. Zoccolotti, P., 1978. Inheritance of ocular dominance. Behavior Genetics, 8: 377-379.

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