Stanley M. Garn

Genetic Control of Sexual Dimorphism in Tooth Size

The existence of sexual dimorphism in the size of the permanent teeth is a well-known attribute of primates, particularly so for the canine teeth, in which the magnitude of the sex difference in the mesiodistal crown diameter may equal 50 percent or even more. However, little attention has been given until recently to the extent of sexual dimorphism in the remaining teeth of various primates and to variations in the magnitude of sexual dimorphism and the patterning of sexual dimorphism in permanent tooth size in various contemporary populations.12 In man, one would postulate either of two conditions for tooth size dimorphism in various populations, the first being identity in patterning but differences in level or variability and the second being variability in patterning as well as variability in magnitude or level. One would also postulate relatively simple genetic control of sexual dimorphism in tooth size, such that the magnitude of difference in the size of the teeth of brothers and sisters would exhibit strong family-line resemblances. One might further postulate a relationship between the magnitude of sexual dimorphism in tooth size and of sexual dimorphism in body size, also best shown by the analysis of brother-sister pairs. Testing these various hypotheses would enable us to go beyond the simple computation of sexual dimorphism in tooth size and beyond population and species comparisons to the analysis of factors controlling the

Variability of Tooth Formation

DATA on the variability of tooth formation are of potential use in a wide variety of applications. With juvenile fossil ancestors of man, teeth alone may have to serve as indicators of age.1 The identification of skeletal remains, cadavers, or amnesia victims may be speeded by good age-estimates utilizing the teeth.2 Where endoerinopathy is known or suspected, comparison of the dental status of individuals with appropriate norms may be of potential diagnostic value, and may help to elucidate the effects of endocrine secretions on tooth development.3 , 5 It is useful, therefore, to have adequate information on the normal range of variability of tooth formation, using either the +2 af limits currently accepted6 or other limits, precisely defined. The literature prior to 1930 provides little assistance in this task. Although there is no lack of tables, the accuracy of the early estimates is open to question, and ranges of variability are almost totally lacking. The tables of Pierce.7 Black,8 and Legros and Magitot9 10 simply do not agree with clinical experience. The atlas of Remington, and the trilingual photographic atlas of Witzel11 are beautifully printed, but inadequate, as is the tabulation reprinted by Churchill in 1933.2 Most contemporary references to tooth formation and the variability of tooth formation are derived from the studies of Logan and Kronfeld,13 and the table published by Kronfeld in 1935.14 Areys table, as printed in Developmental Anatomy (ed. 6, 195715) is clearly modified from Kronfelds although not so designated. Wilkins attributes his Table VI (Ref. 16, p. 38) to Holt and McIntosh,17 and they (via Schour and Massler1l) to Kronfeld.14 The norms for tooth formation in The Handbook of Biological Data6 are evidently derived from Kronfeld14 through Schour and Massler. Thus, any worker who wishes information on the variability of tooth formation knowingly or unknowingly makes use of the Logan-Kronfeld data and the Kronfeld values. However, in the course of our longitudinal investigations on the development of the secondary dentition, we encountered increasing evidence that the Logan-Kronfeld ranges were unduly narrow. Many children in our series fell outside of the published ranges, occasionally by as much as 3 to 4 years. Accordingly, we prepared new estimates of variability for 3 stages of 5 posterior teeth, and found a much larger range of variability than had been

The Sex Difference in Tooth Calcification

DURING the years of growth and development, girls are advanced over boys in a great many respects. They are earlier, on the average, in appearance of ossification centers; they are ahead in epiphysial union and the appearance of secondary sexual characteristics. While the direction of sexual dimorphism in the deciduous dentition may be somewhat questionable, the fact that girls tend to be earlier in eruption of the permanent teeth is not. For white children of European ancestry, the average sex difference in the time of eruption is 0.45 year (or nearly 5 per cent) with a maximum of 0.93 year (9 per cent) for the mandibular canine tooth.2 Whether comparable or equivalent sex differences exist in tooth calcification is open to question. The most commonly used standards fail to provide an answer. The norms of Logan and Kronfeld,3 based on histologic examinations of jaw sections of 30 children, make no distinction between the sexes; Broadbents roentgenographic standards similarly lump male and female data.5 While the roentgenographic investigations of Gleiser and Hunt on the mandibular first molar6 and Demisch and Wartmann on the mandibular third molar7 both suggest advancement of girls over boys, generalization cannot be made from their studies. It is entirely possible that dental advancement of girls over boys is largely limited to eruption, so that the permanent teeth of girls emerge into the mouth with a lesser degree of calcification. Since, in the course of the Fels Longitudinal investigations, we have amassed serial roentgenograms on a sizable sample of children, exceeding in number the sum of previous studies combined, it seemed pertinent to investigate in detail the question of sex differences in those stages of tooth development not easily accessible to visual examination. The matter of a sex difference and the magnitude of this difference were the problems of primary interest in this investigation.

Bone Measurement in the Differential Diagnosis of Osteopenia and Osteoporosis

Increased or decreased bone formation and bone loss, resulting in the clinical appearance of deficient bone or reduced bone tissue, may be indicated by measurements of (a) total tubular bone width, (b) medullary cavity width, (c) cortical thickness, (d) cortical area, and (e) per cent cortical area. Such measurements are more useful than the general terms “osteopenia” and “osteoporosis.”

The Interrelationships of Serum Cholesterol, Cholesterol Esters and Phospholipids in Health and in Coronary Artery Disease

Serum cholesterol (free, esters and total) and serum phospholipids were determined in 97 men who had experienced coronary heart disease prior to the age of 40, 146 healthy nonhospitalized men of comparable age and a group of 97 men who were matched to the coronary disease group. The mean values for serum cholesterol (total) were 286 mg. per 100 cc., 224 mg. per 100 cc., and 247 mg. per 100 cc. for the coronary disease group, control group and matched control group, respectively. The serum phospholipids were highest in the coronary disease group. It is demonstrated that the interrelationships of the lipids in coronary heart disease are more important than any one of the constituents taken by itself. The theoretic implications of the total cholesterol: phospholipids ratio are considered.

Compact Bone Deficiency in Protein-Calorie Malnutrition

Children hospitalized for acute protein-calorie malnutrition in Guatemala City were not delayed in ossification status as compared with Guatemalan Indian children on their customary low-protein diets, but were markedly and often dramatically deficient in cortical bone.

TYPES AND DISTRIBUTION OF THE HAIR IN MAN

Unlike other taxonomic criteria, hair can be used both to compare man to other primates, and to compare sub-groups of the genus Homo to each other. In the amount of hair, and the number of morphological types of hair, man differs from all other primates, while in the form, distribution, and development of the body hair, racial differences are great. It is not surprising, therefore, that most racial taxonomies have used hair form and distribution, and some classiiications (like Denikers) have made hair the principal criterion of race? As Weidenreich has pointed out, human taxonomies are unique in the importance given to hair: yet no other characteristic that has been employed is more suitable as a sorting criterion. Although the major racial differences in hair form and distribution have been known for a long time, our present knowledge of the form, structure, and distribution is largely limited to the hair of the face, head, and extremities. Until recently, few comparative studies had included data on the hair of. the trunk, and its patterns. Though physical anthropologists have rated hairiness, the categories have remained undefined, and the entire body was rarely included in such ratings. Recently, however, it has become practicable to examine and rate the nude subject, and the attention of anthropologists has therefore shifted from the face and head to the entire body. The pioneer quantitative study of body hair, conducted by Danforth and Trotter over twenty years ago, has been followed by the recent investigation of Dupertuis, Atkinson, and Elftman,6 and studies by the author.6. I These investigations have developed standardized methods for rating body hair, both directly and from photographs. During this time, child-growth studies have contributed data on the growth and development of the adult hair pattern. The appearance of pubic hair, and the development of body hair a t puberty has been studied by Greulich in boyss and by Pryor in girlsQ and has been summarized by Stuart.O Reynolds and Wines have considered the relationship between pubic hair development and maturation, while the relationships between body hair, physique, and sexual dimorphism in the adolescent and young adult have been treated by Bullen and Hardy,2 Sheldon, Tucker, and st even^,^ Bayley and Bayer,I4 and others. Since the studies mentioned have been conducted on draftees, adolescents, and college students in this country, published data is largely confined to young American whites. Now, due to the current interest in body-build, there are available extensive collections of somatotype photographs taken during medical and anthropological examinations, and these photographs are suitable for comparative racial studies of body hair, as well as investigations of hair changes in older age groups. Body-build photographs now on file include extensive series of American whites, Negroes, Chinese, Japanese,16 Navajo,*B Aleut,I7 and Micronesians.Is Reports on the body-

X-linked Inheritance of Tooth Size

In the course of previous studies on the genetics of tooth formation and movement timing1 2 we have encountered evidence suggestive of X-mediated inheritance.8- These findings have raised the question of whether calcification, movement, and apical closure alone indicated sex-chromosomal involvement or whether tooth size and tooth morphology might also reveal evidence of X-chromosomal mediation. The present report, therefore, is concerned with tooth size in siblings of like-sex and unlike-sex. The mesiodistal tooth measurements were completed before the specific hypothesis was advanced for testing and therefore were free of unconscious bias in this respect.

Sexual Dimorphism in the Buccolingual Tooth Diameter

In recent years attention has been given to mechanisms controlling over-all tooth size. Reduction in tooth number has been related to reduced size and morphological complexity of the remaining teeth (S. M. GARN, A. B. LEwis, and R. S. KEREWSKY, Nature, 200:488, 1963; H. J. KEENE, Angle Orthodont., 35:289, 1965; K. HANIHARA, T. MASUDA, and T. TANAKA, J. Anthropol. Soc. [Nipponj, 73:72, 1965). While sex clearly affects tooth size throughout the dentition, dimorphism is particularly large for

Sibling Similarities in Dental Development

Numerous aspects of the human dentition have been subjected to genetical analysis. Besides caries susceptibility, these include tooth size, tooth morphology, the time oferuption of the teeth, and, finally, the rate of development of the teeth within the jaws. Tooth form does appear to be largely gene-determined, as studies of cusp pattern, crown morphology, and root shape suggest. 2 The size of the teeth may also be listed among those traits primarily under genetic control, even though twin concordance in crown diameters of the anterior teeth falls short of perfection.34 For the timing of tooth eruption there are at least inferential data, derived from comparative studies, that point to some degree of genic control.56 However, information on twin and sibling similarities in the rate of tooth formation and comparative racial data on tooth formation are almost completely lacking.7 We have, therefore, extended our earlier studies on sibling similarities in the sequence of calcification7 to similar family-line analysis of similarities in the timing of tooth calcification and tooth movement. Our purpose has been to determine whether and to what extent tooth development shows evidence of genic control.