ABSTRACT
The ratio of 2nd to 4th digit length (2D:4D), the systemizing quotient (SQ) and the empathizing quotient (EQ) are commonly put forth as correlates of prenatal testosterone. However, the evidence that 2D:4D is related to SQ or EQ is mixed. Indirect finger measurements were used and no significant associations with 2D:4D and SQ or EQ was found, whereas significant correlations between 2D:4D and a composite measure of SQ and EQ using direct finger measurements was reported. This study aimed at reporting associations of traits largely determined in-utero (2D:4D), SQ, EQ and other anthropometric indices in participants from two ethnic groups, namely Bajju and Asholio of Kaduna state. SQ and EQ were assessed in 600 participants, 300 from each ethnic group consisting of both males and females, using a questionnaire of 120 questions. Body anthropometrics such as height, weight, hip, waist, chest circumference were measured using stadiometer and measuring tape. Digit lengths of the second and fourth fingers were directly measured from the proximal crease to the tip of the finger using vernier caliper. Digit ratio was found to be significantly lower in males than females in both ethnic groups (right hand; males: 0.964 ± 0.050, females: 0.987 ± 0.054, t = 2.579, p = 0.010, : left hand; males: n = 0.984 ± 0.040, females: n = 1.011 ± 0.039, t = 4.549, p = .0001).There was significant negative correlation between SQ and 2D:4D and this being stronger for right hand (right r = -0.18, left; r = -0.08, p < 0.01 and 0.05) and independent of weight, age, height, ethnicity, body mass index, waist-hip ratio, waist-chest ratio and education. There was no significant correlation between EQ and left and right 2D:4D (right r = 0.13, left; r = 0.11, p > 0.01 and 0.05) , right hand 2D:4D being the major predictor of SQ (B=0.154, p=0.00). Significant positive correlations was found between female‘s left and right hand 2D:4D, waist and hip circumference, and WCR (right r = 0.12, 0.26, 0.19 left; r = 0.10, 0.26, 0.25 p < 0.01 and 0.05). (v) BMI has no relation with right ratio in the female, is negatively related to left hand 2D:4D but insignificant (right r = 0.13, left; r = -0.013, p > 0.01 and 0.05). In
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conclusion, it is found that right hand 2D:4D was negatively correlated with SQ in males and females. The relationship was strong to the effects of sex, age, height and education. This suggests that 2D:4D and SQ are influenced by Prenatal Testosterone at similar developmental times. There was no association between 2D:4D and EQ. Birth order and family size shows effect on SQ and EQ
TABLE OF CONTENTS
Title Page – – – – – – – – – – i Declaration – – – – – – – – – – ii Approval page – – – – – – – – – iii Acknowledgement – – – – – – – – – iv Dedication – – – – – – – – – – vi Table of Content – – – – – – – – – vii List of Tables – – – – – – – – – xi List of Figures – – – – – – – – – xiii List of Appendices – – – – – – – – – xiv Abstract – – – – – – – – – xv 1.0 INTRODUCTION – – – – – – – – 1 1.1 Background to the Study – – – – – – – 1 1.2 Brief Ethnography of Bajju and Asholio – – – – – 6 1.2.1 History – – – – – – – – – 6 1.2.2 Main cities and towns – – – – – – – 6 1.2.3 Weather and Climate – – – – – – – – 6 1.2.4 Land mass, location and population – – – – – – 9 1.2.5 Original inhabitants and settlers – – – – – – 9
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1.2.6 Administrative structure – – – – – – – 9 1.2.7 Ethnic composition, culture and the arts – – – – – 10 1.2.8 Population structure and distribution – – – – – – 10 1.2.9 Urban and rural development and patterns of human settlement – – 11 1.3 Statement of Research Problem – – – – – – 12 1.4 Justification of study – – – – – – – 12 1.5 Aim and Objectives of Study – – – – – – 13 1.6 Significance of Study – – – – – – – 13 1.7 Study Hypotheses – – – – – – – – 14 2.0 LITERATURE REVIEW – – – – – – – 15 2.1 History of Digit Ratio Research – – – – – – 15 2.2 Assessment of Digit Ratio – – – – – – – 16 2.3 Digit Ratio Distribution – – – – – – – 17 2.4 Evidence of Androgen Effect on Digit Ratio – – – – 18 2.5 Geographic and Ethnic Variation in Digit Ratio – – – – 20 2.6 Correlation between Digit Ratio and Traits – – – – 21 2.7 Correlation between Digit Ratio and Muscular Endurance – – 24
2.8 Correlation between Digit Ratio and Jealousy – – – – 27
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2.9 Correlation between Digit Ratio and Male Ability in Sports – – 30 2.10 Correlation between Digit Ratio and Facial Attractiveness – – 31 2.11 Correlation between Digit Ratio and Traffic Violations – – – 33 2.12 Digit Ratio and Play Behaviour in Children – – – – 36 2.13 Digit Ratio, Cognitive Styles and Facial Emotion Recognition – – 40 2.14 Body Mass Index, Weight, Height and Digit Ratio – – – 42 2.15 Digit Ratio and Risk Taking – – – – – – 43 2.16 Male to Female Transsexual People – – – – – 45 2.17 Digit Ratio and Development – – – – – – 45 2.18 Empathizing-Systemizing Theory – – – – – – 45 2.19 Fetal Testosterone – – – – – – – – 53 2.20 Evolutionary Explanation for Sex Difference – – – – 53 2.21 Extreme Male Brain Theory of Autism – – – – – 54 2.22 Imprinted Brain Theory – – – – – – – 56 3.0 MATERIALS AND METHODS – – – – – – 57 3.1 Research Participants – – – – – – – 57 3.3 Methodology – – – – – – – – 57 3.4 Sampling Size Determintion- – – – – – 58 3.5 Systemizing Quotient and Empathizing Quotient – – – – 59 3.6 Data collection technique – – – – – – 60 3.7 Anthropometry – – – – – – – – 61 3.8 Ethical Approval – – – – – – – – 62
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3.9 Inclusion and Exclusion Criteria- – 62 3.10 Statistical Analyses – – – – – – – – 63 4.0 RESULTS – – – – – – – – – 64 5.0 DISCUSSION – – – – – – – – – 104 6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS – – 110 6.1 Summary – – – – – – – – – – 110 6.2 Conclusion – – – – – – – – – 112 6.3 Recommendations – – – – – – – – 113 REFERENCES – – – – – – – – – 114 APPENDICES – – – – – – – – – 139
CHAPTER ONE
1.0 INTRODUCTION 1.1 BACKGROUND OF THE STUDY
Digit ratio is the ratio of the lengths of different digits or fingers typically measured from the midpoint of proximal crease where the finger joins the hand to the tip of the finger (Mayhew et al., 2007). An individual’s fingers and toes begin to develop in the 6th week of pregnancy. Digit ratios are determined while the embryo forms and will then remain the same without change during individual development (Manninget al., 2004). The fetus grows quickly from the 9th week of pregnancy, and this is the sensitive period for fetal development. The major feature of the fetal period is cell differentiation, which is sensitive to external environmental changes. So during this period, if the fetus encounters changes in the intra-uterine environment, such as intra-uterine under-nutrition or hormone level changes, not only will the fetal structures of the organs and organism be changed, but also the development of fetal fingers and toes will be affected (Manning et al., 2004). Exposure to different levels of sex hormones in-utero leaves effects on human fingers (Manninget al.,1998). People exposed to elevated levels of testosterone tend to have ring fingers (the fourth digit: 4D) longer than their index fingers (the second digit: 2D). Estrogen exposure has the opposite effect; the index finger tends to be longer than the ring finger. Therefore, the ratio between the length of second and fourth manual digits (2D:4D) is a sexually dimorphic trait—males tend to have lower 2D:4D values that females (Manninget al.,1998) and it is a cross-cultural trait (Manninget al., 2003; Manning et al., 2004).2D and 4D ratio showed significant relationship with height, weight, chest, waist and hip circumferences in a study of sexual dimorphism in Nigerians (Danborno et al., 2007). The study strongly confirms the sexually dimorphic nature of 2D:4D ratio. Even though it failed to show relationship between 2D:4D, BMI, chest, waist and hip circumferences as reported in other studies (Danborno et al., 2007). (Gwunireama et al., 2010)
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confirmed that digit ratio is sexually dimorphic and represents the original data for the people of the Niger Delta. The result of the 2D:4D ratios of the Ebira ethnic group showed that the 2D:4D ratio of females was greater than the digit ratio of the males and also the digit ratios has no relationship with either height, weight or BMI of an individual and represents the original data for the people of the Ebira tribe of Nigeria (Ibegbu et al., 2012).
Baron-Cohen (2003) proposed a theory which encompasses two different styles of thinking or ‗cognitive styles‘ namely systemizing and empathizing. Systemizing is the drive to analyse and explore a system, to extract underlying rules that govern the behavior of a system and the drive to construct systems. Whereas empathizing is the drive to identify the thoughts and emotions of others and respond appropriately (Baron- Cohen, 2002, 2003; Baron-Cohen et al., 2003).Cognitive styles in the current context should not be confused with the same term that cognitive psychologists traditionally conceptualized as the way someone perceives and remember information along a dimension (Kozhevnikov, 2007). While the two definition might share similar or overlapping characteristics, Baron-Cohen‘s conceptualization of cognitive style is born out of the volume of work with autistic children and endeavors to explain functional and cognitive differences between individuals with and without autistic traits. Males on average score higher on tests of systemizing and females usually score higher on tests of empathy (Baron-Cohen, 2002, 2003). These sex differences may arise as a result of the influence of Prenatal testosterone PT acting on the fetus such that it has an organizing effect on the brain and thus facilitates the ability in systemizing but reduces the ability to emphasize. Males develop a lower 2D:4D than females by the end of the first trimester of gestation (Malas et al., 2006; Galis et al., 2010). Because of the early fetal development of sexualdimorphismin2D:4D ratio, it is suggested that 2D:4D ratio may serve as a biomarker for prenatal androgen exposure (Manning et al., 1998; Lutchmaya et al., 2004; Gallup et al.,2008).Over
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the past few years, this hypothesis has generated much interdisciplinary research interest (Gallup et al., 2008; Voracek et al., 2009). 2D:4D was shown to be a correlate of a multitude of sex-dependent, hormonally influenced variables such as behavioral, cognitive, personality, and somatic traits, adult onset disorders, and measures related to fertility and sexuality (Manning, 2002).
Many studies showed that low 2D:4D ratios correlated with athletic ability (Manninget al., 2001; Manning et al., 2007) and male aggression (Bailey and Hurd2005; McIntyre et al., 2007).In a study conducted among the Nigerian population, showed males have a significantly negative relationship between right and left 2D:4D ratio with birth weight, while females show positively significant relationship in both right and left hands. This means that association exists between 2D:4D ratio and birth weight which could be predicted most especially from the left hands (Danborno et al., 2010). On the other hand, results regarding other variables were less homogenous. For example, some studies investigating relations between finger digit ratios and sexual orientation reported that homosexual men have higher 2D:4D ratio than heterosexual men (McFadden et al., 2002; Manning et al., 2007), some homosexual men have lower 2D:4D ratio than heterosexual men (Rahman et al., 2003; Rahman, 2005), and others showed that there was no significant difference between 2D:4D ratio in homo- and heterosexual men (Williams et al.,2000; Voracek et al., 2007). The latest meta-analysis regarding 2D:4D and sexual orientation (Grimbos et al., 2010) showed that there was no difference between heterosexual and gay men (but heterosexual women had more feminine 2D:4D ratio than did lesbians). Additionally, ethnicity explained some between-studies variation in men. Cross-racial differences in sexual dimorphism of 2D:4D is poorly investigated. Surprisingly, 2D:4D varies across nations and these cross-national differences are noticeably larger than the sex differences found within nations (Manning et al., 2007; Manning et al., 2000, 2003, 2004). As Voracek and Dressler (2006) discussed, these differences are poorly understood and, therefore,
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cross-cultural studies concerning 2D:4D are still interesting. Until 2006, samples from more than 25 different countries or ethnic groups were collected and investigated, but the participants were mainly White (Voraceket al., 2006). Human digits are numbered consecutively from 1 (thumb) to 5 (little finger). Because thumb length is difficult to measure, digit ratio generally just includes the six ratios of digit lengths, being 2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D and 4D:5D (Manning 2002). In 2000, a related paper published in Nature introduced studies on digit ratio, and pointed out that ―finger length ratio may reveal some surprising information of development‖(Williams et al., 2000). Accordingly, numerous studies have found associations between digit ratio and sexually dimorphic variables including – but not limited to – aggression, gender self-concept, stimulation seeking traits, nociception, and sporting ability (Fink et al., 2006; Hampson et al., 2008; Manning, 2002; Schmukle et al., 2007; Schwerdtfeger et al., 2008; Tester et al., 2007).Recently researchers have been trying to investigate the relationship between 2D:4D and traits like coronary heart disease (Fink et al, 2006), gym-based physical fitness (Hoenekopp et al., 2006), development of psychopathology (Fink et al., 2007), cooperative behaviour (Millet et al., 2006), attention deficit hyperactivity disorder (Stevenson et al., 2007).
Progress has been rapid in describing the traits of digit ratio, especially the second to fourth digits (2D:4D) and its correlation studies in humans. It has been shown in early studies that 2D:4D differ between the genders. Males have lower 2D:4D ratio than females. It is generally assumed that this difference is established during early prenatal development under the influence of sex hormones. This view has illustrated by the recent experimental mouse work of (Zheng and Martin 2011:
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Manning 2011). They revealed that the sex differences in 2D:4D were the results of prenatal testosterone (PT) and prenatal estrogen (PE) signaling in a narrow developmental time window in utero. Furthermore, an evidence suggests that in the human male, fetus starts to produce testosterone in week 8 and testosterone peaks at about week 11 or 12 to 14 (Scott et al., 2009). The 2D:4D ratio is probably fixed during this tight time (Mallas et al., 2006). Because of this, there has been increasing use of the 2D:4D ratio as an index of prenatal hormone exposure, and extensive studies in humans have found correlations between digits ratios and a variety of physiological and psychological conditions, including fertility, athletic ability, sex-biased diseases, social behaviors, and sexual orientation (Manninget al., 2003: Zheng and Martin 2011). Over the last decade, studies of 2D:4D ratio of many different populations have suggested a link between developmental stability and organism’s general health and reproductive fitness (Roney et al., 2004). Manning et al.,reported that 2D:4D was related to fertility in men (Manning et al 1999: Manninget al., 2004). Low 2D:4D values in the right hand were associated with high sperm counts and high concentrations of testosterone. This finding is in agreement with earlier study by Wood (Wood et al., 2003) on ICSI of sperm. However, (Firman et al., 2003; Bang et al., 2005) reported no association between 2D:4D and sperm parameters in men from the general population. In contrast, (Augeret al., 2010) reported a week but significant positive association between low 2D:4D and fertility in a general population sample.
Manning and colleagues have shown that 2D:4D ratios vary greatly between different ethnic groups (Manning et al., 2004) This variation is far larger than the differences between sexes; in Manning’s words, “There‘s more difference between a Pole and a Finn than a man and a woman.”(Terrance et al., 2000).
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1.2 STUDY LOCATION The study was conducted in Ahmadu Bello University, Zaria, Kaduna State University, Nuhu Bamalli polytechnic and College of Education Gidan -waya Kaduna state. 1.2.1 History Kaduna State was originally part of the Northern region in the three-region structure of 1954. In 1967, with the creation of twelve federal states by General Yakubu Gowon’s Military Government, Kaduna State became part of North-Central State. The 1976 Military Government of General Murtala Muhammed created nineteen states from the existing twelve and North-Central State was renamed Kaduna State. In 1987, General Ibrahim Babangida’s Military Government brought the number of states to twenty-one and Kaduna was divided into Kaduna and Katsina states. 1.2.2 Main Cities and Towns Kaduna (capital city), Zaria, Kagoro, Kafanchan, Kachia and Zonkwa.Kaduna State is one of the seven states that make up the North West geopolitical zone of Nigeria. It has interstate boundaries with Niger State to the west, Zamfara, Katsina and Kano states to the north, Bauchi and Plateau states to the east and FCT Abuja and Nasarawa State to the south.
1.2.3 Weather/Climate
The state is located in a tropical rain forest zone and has a tropical savannah climate. The climate is humid and the humidity is at its highest between March and November. For the whole Kaduna State the mean daily temperature is 32.7°C (80.1°F). As in the rest of West Africa, there are only two types of weather periods, rainy season and dry season.
The average annual rainfall in the area is around 1,500 millimetres (79in), which arrives intermittently and becomes very heavy during the rainy season. Other weather conditions affecting
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the state include Harmattan, a dusty trade wind lasting a few weeks of December and January. Like the rest of Nigeria, the state is hot all year round.
Fig. 2: Map of Nigeria showing a Kaduna State
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Figure 3: Map of Kaduna state showing the Asholio and Bajju LGA as Kaura and Zangon-Kata
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1.2.4 Land Mass, Location and Population Kaduna State lies at latitude 10°20′ north and longitude 7°45′ east and covers an area of 45,711.2 square kilometres. It has a population of 6,113,503 (2006 census figures) and a population density of 130 people per square kilometre. It accounts for 4.3% of Nigeria’s total population. 1.2.5 Original Inhabitants and Settlers The early settlers of Kaduna State were the Atyap (who occupy its southern part) and the Gbagyi peoples. Archaeological finds show that Kaduna State was home to the ancient Nok civilisation which dates back to 500AD. The main ethnic groups in Kaduna State are the Gbagyi, Hausa, Kamuku, Kadara and Kurama. Fifty-seven languages are spoken in the state; of these, Gbari and Hausa are the major ones. Christianity and Islam are the main religions in Kaduna State, although a fair amount of traditional religion is practised.
1.2.6 Administrative Structure There are 23 Local Government Areas (LGAs) in the state. Each has a chairman as its administrative head. Local Government Areas in Kaduna states are Birni-Gwari, Chikun, Giwa, Igabi, Kajuru, Ikara, Jaba, Kachia, Jema’a, Kaduna North, Kaduna South, Kagarko, Kaura, Kauru, Kubau, Kudan, Lere, Makarfi, Sabon-Gari, Sanga, Soba, Zango-Kataf, Zaria.
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1.2.7 Ethnic Composition, Culture and the Arts Apart from the six major ethnic groups found in the State, there are over twenty other ethnic minority groups, each with its language and arts or religion different from the other. Works of art and pottery (e.g. the “Nok Terracotta”) found in the southern parts suggest that it is a major cultural centre. Among the major ethnic groups are Kamuku, Gwari, and Kadara in the west, Hausa and Kurama to the north and Northeast. “Nerzit” is now used to describe the Jaba, Kaje, Koro, Kamanton, Kataf, Morwa and Chawai instead of the derogatory term “southern Zaria people”. Also, the term “Hausawa” is used to describe the people of Igabi, ikara, Giwa and Makarti LGAs, which include a large proportion of rural dwellers who are strictly “Maguzawas.” In the north, the Hausa and some immigrants from the southern states practice Islam and majority of the people in the southern LGAs profess Christianity. The major Muslim festivals are the “Salah” celebrations while Christmas, New Year and Easter are observed by the Christians. Two traditional festivals of significance are the “TukHam” and “Afan” in Jaba and Jama’a LGAs respectively. Prominent among the traditional arts, are leather works, pottery and indigopit dyeing with Zaria as the major centre. 1.2.8 Population Structure and Distribution Although majority of Kaduna State population live and depend on the rural areas, about a third of the State’s populations are located in the two major urban centres of Kaduna and Zaria. However, except in the northwestern quadrant, the rural population concentration is moderate, reaching a high of over 500 persons per sq. km. in Kaduna/Zaria and the neighbouring villages; 350 in Jaba, Igabi and Giwa and 200 in Ikara LGAs. Despite the provisional nature of the census results, observations of movements of young able bodied male labourers in large numbers, from rural
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villages to towns during the dry season and back to rural agriculture fields during the wet season, suggest a sizeable seasonal labour force migration in the state. However, the seasonal labour migration has no effect on agricultural labour demands in the rural traditional setting. Indeed, some of these seasonal migrants come to town to learn specific trade or acquire special training and eventually go back to establish in the rural areas as skilled workers (e.g. masons, technicians, tractor drivers, carpenters, motor mechanics, etc). Another major feature of the State’s population structure is the near 1:1 male/female ratio, not just for the state as a whole, but even among all the LGAs. The effects of this may be helpful to the future social and economic development of the rural sector especially in the agro allied rural industries. The large number of secondary school leavers, polytechnic and university graduates provides a growing skilled labour force for the growing industries in the State. 1.2.9 Urban and Rural Development and Patterns of Human Settlement: The pattern of human settlement throughout the State is tied to the historical, political and socioeconomic forces the area has been subjected to, from the precolonial to post colonial period. Prior to the advent of the British occupation, the basic unit of human settlement was the extended family compound. As compounds grew, the needs for security and defense led to a higher hierarchy of settlements called “Garuruka” (towns). These towns were protected by walls with a titled/administrative head appointed by higher political authority, the “Sarki”. This pattern of settlement dominated the Hausawa cultural groups to the north (i.e. Giwa, Igabi, Zaria, Sabon Gari, Kudan, Makarfi and parts of lkara LGAs). Higher settlement hierarchy than the rural extended family compounds in other parts of the state was delayed, until the development of social amenities
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and infrastructure such as motor and rail road, Christian Missionary establishments and recently, produce buyers, markets and administrative reorganizations gave impetus (settlements such as Birnin Gwari, Kuda’a, Kachia, Zango Kataf, Kwoi, Sambam, Kagoma and Saminaka are good examples). 1.3 STATEMENT OF RESEARCH PROBLEMS The ratio of the length of the second to fourth digit (2D:4D ratio) presumably reflects prenatal exposure to sex hormones. The 2D:4D ratio is sexually dimorphic, and males consistently have a slightly lower value (Manning et al., 1998). It is associated with many behavioral and biological variables, including fertility and sexual behavior but few studies have focused on its association with psychosocial traits like systemizing and empathy particularly among the Bajju and Asholio tribes.. Therefore, there is paucity of reference values for direct association between Second to fourth digit ratio, systemizing and empathizing in Bajju and Asholio population of Kaduna state. Hence the need to carry out this research to fill this gap. 1.4 JUSTIFICATION There are indications that 2D:4D ratios correlate with aggression, dominance, sporting ability, fertility problems, number of children, health status, sexual orientation and other variables related to reproductive success. Therefore the need to correlate 2D:4D ratio, BMI, empathizing and systemizing among these ethnic groups is desirable. Results of this study may provide reference for the use of 2D:4D ratio in psychoanalysis of individuals. It may also confirm systemizing and empathy quotient as behavioural marker for prenatal testosterone.
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1.5 SIGNIFICANCE OF STUDY Digit ratio has been reported by many workers to show sexual dimorphism with women having higher ratio than men (Phelps 1952, Manning et al., 1998, Manning et al., 2002). This study will provide information about the digit ratio of Asholio and Bajju young adults and its association with systemizing, empathy and BMI. Can also provide functional index of nutritional status and social rehabilitation. The result of the present study will also show the influence of anthropometric indexes, ethnicity, geographical location, digit ratio on systemizing and empathy. 1.6 AIMS AND OBJECTIVES 1.6.1 AIM OF THE STUDY The aim of this study is to evaluate the association of 2D:4D, empathizing, systemizing and anthropometric indexes among the Bajju and Asholio tribes in Kaduna state. 1.6.2 OBJECTIVES OF STUDY The objectives of the present study is to investigate:
i. Sexual dimorphism in 2D:4D ratio amongst the Bajju and Asholio people.
ii. Ethnic difference in 2D:4D ratio between the Bajju and Ashilio groups.
iii. The relationship between 2D:4D ratio and BMI.
iv. The relationship between systemizing, empathizing and 2D:4D ratio.
v. Ethnic difference in systemizing and empathizing between the Bajju and Ashilio groups.
vi. The influence of education on empathizing and systemizing.
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1.7 STUDY HYPOTHESIS There will be sexual dimorphism in 2D:4D ratio, relationship between 2D:4D ratio with systemizing and empathizing behaviours amongst Bajju and Asholio people of Kaduna State, Northen Nigeria.
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