Sexual dimorphism and its forensic implications in human lanugo and vellus hair

Abstract

Hair as an exoskeleton is a unique characteristic of mammals; Human hair is a highly versatile material with significant potential in several areas such as population classification, forensic science for personal identification and also from evolutionary perspectives. Many research reported sexual dimorphism of quantitative characters in adult terminal hair and thereby provided imperative roles in evolutionary aspects and personal identification. Apart from the three phases to hair growth such as anagen, catagen and telogen phases, the age of hair can be divided into three types such as the first hair, known as lanugo begins to grow on the entire body of the embryo at 3-4 months of pregnancy and falls out within 7-8 months, followed by vellus and terminal hair. To best of the knowledge this is the first attempt on Histomorphological and Quantitative variation of lanugo Hair consisted of 250 lanugo hair strands (125 males and 125 females) obtained from spontaneously aborted fetus (around 3 months) and 1650 vellus hair strands (Male 800 and female 850) obtained from the newborns. Before microscopy for histomorphological (medullation) and quantitative aspects (hair length in mm and shaft diameter in µm), each hair strands were washed and cleaned following standard technique. The result demonstrated no histomorphological variation in lanugo hairs for both the sexes, since all strands were non-medullated. But in contrary to lanugo hair strands, vellus hairs showed medullated hair strands with significant (p<0.05) lower incidences in comparison to non-medullated scalp hair for both the sexes. However, the incidences of shaft diameter demonstrated significant (p<0.05) sexual variation (dimorphism) in terms of higher shaft diameter in vellus scalp hair among the females. The quantitative characteristic for example, hair length also demonstrated significant (p<0.05) sexual dimorphism indicating of higher vellus scalp hair length among the females than the males. Unlike the lanugo hair, the vellus hair revealed significant (p <0.05) sexual dimorphism for the both the hair length and shaft diameter. Interestingly, the present research vindicated significant (p<0.05) effect of hair growth (length and shaft diameter) from lanugo to vellus scalp hair for both the sexes. Therefore, the present study envisaged the sexual variation in fetal scalp hair for both the qualitative and quantitative aspects could have forensic implications.