Human ears grow throughout the entire lifetime according to complicated and sexually dimorphic patterns - conclusions from a cross-sectional analysis
Niemitz, Carsten;Nibbrig, Maike;Zacher, Vanessa
In most of its anatomical constituents, e.g.in the Helix, etc., the external human ear is homologous to that of all Primates and Scandentia(tree shrews). Thus, its genetic basis is largely older than 60 Mio yrs. Based upon the observation of lifelong growth of the ear(e.g.Montacer-Kuhssary 1959), we aimed to elucidate the growth of the human ear in a more detailed way throughout life and in both sexes. On standardized photographical material collected randomly in Berlin(Germany), we measured N=1448 ears from neonate children to volunteers of 92 yrs in age. 10 longitudinal measurements and 5 further anatomical parameters yielded a data set of roughly 19,000 data in total. Based upon our cross-section analysis, we quantified several sexual dimorphisms. Furthermore, we deduced ontogenetic developments and, partially, corrected their proportions for secular acceleration and body height shrinking with age. At the time of birth, in proportion to the body, the external ear was even bigger than the large head and continued growing rather linearly throughout life, reaching the highest average lengths in the volunteers aged over 85 yrs. The large yearly increases during childhood began to diminish at as early an age as 8 or 10 yrs. In all parameters where post adult growth was observed, female ears showed a lesser increase than those of men. The greatest ear length in females was 52 mm(SD-4.3 mm)at birth, 61 mm(SD-3.9 mm)at around 20 yrs of age and 72 mm(SD-4.6 mm)in women older than 70 yrs. For the male subjects, these three values were:52 mm(SD- 4.1 mm),65 mm(SD -4.0 mm)and 78 mm(SD-4.8 mm), respectively. In spite of extreme premature growth of the auricle and its further lifelong growth, three anatomical features of the ear did practically not grow at all after birth:the width of the Concha auriculae and of the Incisura intertragica, as well as the diameter of the helical brim of the auricle. The problems arising concerning the functions and selective values of all these very unusual proportions and growths are discussed. The ontogenetic development of one or more pretragal skin folds could be used as a contribution to age estimations in forensic anthropology.