BIOGEOCHEMICAL RECORD OF ANCIENT HUMANS

The geochemical record of humans extends back to their first appearanc e on the landscape some one million years ago. Biochemical remains fro m humans, however, can be found in the fossil record for only the last 100 000 years, and even then these remains are only fragmentary. Stab le carbon and nitrogen isotopes in organic and inorganic fossils of hu mans are providing a great source of information on ancient human biog eochemistry. Two case studies demonstrating the utility of isotopic an alyses for tracing the history of human behavior are presented. In the first, human skeletons from Easter Island were analyzed to determine whether the diet included foods from the marine environment. Isotopic records show that a sizeable influence from marine N can be detected i n the ecosystem of this island. In a second study, the duration of nur sing by prehistoric people was pinpointed with isotopic analysis. A st udy of modern humans was compared with analyses of two skeletal popula tions - Archaic Indians living 5000 years BP and Plains Indians from 1 600 AD. Duration of nursing was the same in both populations, even tho ugh the Archaic Indians did not practice horticulture, whereas the Pla ins Indians grew crops. The geochemical record on the population growt h of the human species has many implications. Recent developments incl ude the analysis of stable isotopes in individual compounds from human remains. Carbon and nitrogen isotopic compositions of amino acids-hav e been used to determine the source of dietary C with a C-4 plant infl uence on human collagen. Also, the relative distribution of C and N is otopes in amino acids of these humans is compared with those in collag en from modern humans. Human diet and feeding behavior differ from tha t of almost all other animals (with the exception of primates and poss ibly cetaceans), because of the human's ability to think and resulting societal pressures. Finally, when human remains are scarce, the searc h for human activity reverts to materials that serve as proxies for pa leostudies. The future of this field lies in expanding tools of biomed icine to the study of ancient DNA. Expansion of isotopic techniques in cludes the study of lipids in skeletal remains and associated archaeol ogical materials. The challenge will be to broaden the techniques and samples available for analysis to proxy materials not directly associa ted with skeletal remains so that an even older human record can be re ad. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.