Mixture Analysis and its Preliminary Application in Archaeology

Abstract

Sexual dimorphism has been a special concern in human origins studies. Not only must sexual dimorphism be considered in attempts to determine sex ratios in archaeological faunal materials and prehistoric human population samples, but assessing the nature and degree of sexual dimorphism in various hominid species in the past can be crucial for understanding the nature and rate of hominid evolutionary change and sometimes to a certain degree for making species designations among (hominid or other) specimens. Obtaining sex ratio in a population is easy if each individual in the population can be accurately sexed through the use of one or more objective variables. But this is often impossible, due to the incompleteness of the osteological record. One does not, however, have to sex each individual in a population in order to “sex the population”. Mixture analysis is a statistical method that can be used to deal with the problem of sexing the population without knowing the sex of any individual member.This paper introduces some basic concepts and procedures of mixture analysis, gives a brief review of its development and previous applications in various fields, discusses some preliminary results of its application to the tooth metric data of African early hominids, of the Lufeng hominoids and of the two cervid species (Megaloceros pachyosteusandPseudaxis grayi) from theHomo erectussite at Zhoukoudian Locality 1. The quantitative results of this research are compared to previous qualitative assessments of the same materials. A control study to test the power of mixture analysis to discriminate sexual dimorphism was conducted on metric dental data from modern great apes, the results compared to the known metric patterns.Analysis of hominid/hominoid tooth data indicates that there are more males than females inA. robustusand more females than males inA. afarensis; there appears to be more than one species of hominoid represented at the site of Lufeng in China; and there are more females than males in the alleged smaller species among the Lufeng hominoids. The analysis of cervids from Zhoukoudian Locality 1 suggests that there are more females than males for theMegaloceros pachyosteusand more males than females for thePseudaxis grayi;Pseudaxis grayiis dentally more sexual dimorphic thanMegaloceros pachyosteus. The analysis shows that mixture analysis has great potential for determining sex ratios and the degree of sexual dimorphism for zooarchaeological and palaeontological researches.