Abstract: problem of distinguishing the earliest Man from his fellow primates. One criterion suggested was brain size; another, the ability to make tools. Agreement was not reached. And at that time evidence was accumulating that primates with smaller brains made tools earlier than had been sup posed?seeming to push the origin of Man back considerably in time, and making distinguishing criteria even more uncertain. But, after all, should we expect, using any criteria whatsoever, to be able to pin-point the exact moment of origin of Man, any more than could Archbishop Usscher, who placed it at 4004 b. c? More than a few genetic steps must separate Man from his nearest known primate relatives, and even though each step itself was an abrupt one, all did not occur, or manifest them selves, simultaneously. So any choice of a moment of emergence must be arbitrary, and may be misleading if we let it color our ideas of subsequent events. Is it not better to think of this, and other evolutionary origins, as vague periods of transition at the end of which categories have appeared that could not have been distinguished before, and the exact path to which is not traceable?1 From fossil remains the more manlike Australopithecus may be easily distinguished from, say, the more apelike Oreopithecus as a separate though related species having common ancestry (Le Gros Clark, 1955; Simons, 19 0). But even if the one were derived more or less directly from the other there must have been many intermediate forms that have not been discovered, since the fossils that have been collected can be only a meager sample of the populations that have existed. By diligent search fossils of some of these intermediates may be found; but not all, for it is not to be expected that each genetic step will be reflected in gross anatomical features that may be recognized in the fossil record. The transition from one species to another would probably appear quite gradual if we had the whole record before us instead of only those frag ments accidentally preserved. But in the case of Man there is concerned something more than his * I wish to thank The Bollingen Foundation for assistance which made possible the development of the ideas in this paper. 1 Recently m this journal I pointed out some of the difficulties of assigning a moment of origin for living systems (Blum, 1961a). 32

Abstract: Because in most areas traces of all except the most substantial archaeological sites have been removed by alterations in the ground surface, rapid methods of location are of value as a guide to the extent and nature of deposits and the avoidance of relatively uninteresting but otherwise necessary excavation. The presence of sufficient contrast in physical properties between archaeological strata, and between archaeological features and their surroundings, often small or non-existent, is an important factor, which may be complicated by natural contrasts or modern features. The horizontal complexity is also very important, and if great the resultant measured variations are likely to be confused. While one property may show a distinctive variation others may be quite uniform or show misleading changes, hence there is value in cross-checking one method against another. Of the methods used in commercial geophysics, gravity measurement is of little value because of the small scale of archaeological features and their low contrast in density; seismic methods, although of possible use, have not received much attention; but electrical-resistance and magnetic methods are in use. Electrical and seismic methods involve the introduction of a disturbance into the ground followed by measurement of the effects produced, while gravity and magnetic methods measure existing physical properties at points above the ground surface. For routine archaeological work desirable characteristics include simplicity and speed of operation, easy portability, complete self-containment, infrared ray thermometry in investigations of humidity in masonry).