COMMENT: Biology and Body Size in Human Evolution (R.J. Smith)

I wince when estimates of early hominid body weights are accepted without appreciation of their limited reliability. The boundaries of doubt expand when these estimates are applied to problems in relative brain size, megadontia, life history and ecology. Precision does not characterize this line of inquiry. As one who has pursued this line, I appreciate Smith's cautions and can add several other problems to his list of 3. The question arises, is there any value in trying to make and improve these estimates as long as the assumptions are clearly stated? In other words, are they of use in the sense of working hypotheses?

The value of estimating body size and its implications in fossil species can be increased, of course, by following Smith's recommendations. Encephalization could be measured as the relationship between endocranial volume and femoral head size in comparative samples, for example. The reason that body mass plays such an important part of encephalization studies is the fact that the relationship between brain and body weight in humans and other animals has a long history of scholarship. The curious paleontologist can use this richly studied relationship to explore the past. But this exploration cannot stop here and Smith suggests a fruitful area of further research. The same improvements need to be done for all the variables that are now related to body size. Some of us have tried to make a start. Smith cites my 1984 paper (%McHenry, 1984c) as an example of failure to compare tooth area directly with measurements of the fossil remains without going through the process of body weight estimation. That paper tries both approaches: The size of the humerus in extant species of Hominoidea and fossil hominids is related directly to posterior tooth size as well as less directly to body weight.

With these and other improvements, is there value in trying to estimate body proportion and life-history/ecology parameters in fossil species? Of course not, if these variables are taken to approach the precision of estimates on living species. Taking parameters out of tables without reading the cautions in the text must be avoided. They may have value, however, in providing a starting point to examine deviations from expectation. They can show, for example, what the expected home-range area would be based on what is known in living primates (%Milton and May, 1975) and how other evidence contradicts that expectation and explores the implications (%Foley, 1987a). This kind of exploration is helpful, especially in sharpening the focus on human autapomorphies.

I concluded my study of behavioral ecological implications of early hominid body weights by stating that "the dance between precision and uncertainty enlivens paleoanthropology" (%McHenry, 1994a%: 85). With Smith's suggested improvements and clear statement of the errors involved, there remains value in the attempt to reconstruct the past using all approaches including the estimation of relative brain and tooth size, ecological variables, and, with great caution, life-history parameters.

References Cited

Foley, R.A. (1987) Another Unique Species: Patterns in Human Evolutionary Ecology. Harlow: Longman Scientific & Technical.

McHenry, H.M. (1984) Relative cheek-tooth size in Australopithecus. American Journal of Physical Anthropology 64, 297-306.

McHenry, H.M. (1994a) Behavioral ecological implications of early hominid body size. Journal of Human Evolution 27, 77-87.

Milton, K. and May, M.L. (1975) Body weight, diet and home range area in primates. Nature 259, 459-462.

Henry M. McHenry
Department of Anthropology
University of California
Davis, CA 95616
(916) 752-1588
hmmchenry@ucdavis.edu