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AUSTRALOPITHECINE SEX CHANGE

1 M. Brunet, et al., "The First Australopithecine 2,500 Kilometers West of the Rift Valley (Chad)," Nature, 378 (16 November, >1995), 273-275.

See Physical Anthropology: The Core, Chapter 10, pages 237-239, 243-245, 254-255; Physical Anthropology, 6^th edition, Chapter 16, pages 408-409, 414-416, and 418-419.

One of the more complete gracile australopithecine skulls is that of Sts 5 found in 1936 by Robert Broom at the site of Sterkfontein, South Africa. Originally named Pleisanthropus transvaalensis, this well-preserved skull is classified today as Australopithecus africanus, yet retains its original generic name as part of its ickname, "Mrs. Ples." Countless physical anthropologists hold the cast of this fossil in their hands of as they expound on the anatomy of the australopithecine skull.

At the 1995 meeting of the American Association of Physical Anthropologists, several physical anthropologists called the sex of Sts 5 into question.¹ New analysis of sexual dimorphism of the pelvis has led some to conclude that Sts 5 is really a male, and should in the future be referred to as "Mr. Ples."

Is "Lucy" Really a Female?

Martin Hüsler and Peter Schmid of the University of Zurich, Switzerland, made a detailed study of the australopithecine pelvis.² While many fragments of the pelvis are known, only two relatively complete pelvises have been discovered. A third pelvis, from Sterkfontein (STW 43), has recently been discovered, but has not as yet been described. The two pelvises that are complete enough to reconstruct and study are Sts 14 and AL 288-1. Sts 14 is from Sterkfontein and belongs to Australopithecus africanus. AL 288-1 is part of the "Lucy" skeleton from Hadar and is attributed to Australopithecus afarensis.

Both pelvises have some degree of damage and both have critical parts missing. More than one attempt at reconstruction has been made. The differences between the various reconstructions is part of the controversy surrounding the interpretation of the australopithecine anatomy.

Paleoanthropologists are actively debating two major issues in the interpretation of the australopithecines. First, what is the degree of sexual dimorphism and, second, how many species are represented by the fossils that have been recovered to date?

Donald Johanson and others interpret the AL 288-1 skeleton as being that of a female, primarily because of its small size. Larger skeletal elements, including the recently described skull AL 444-2, are thought to represent the A. afarensis male. Some paleoanthropologists explain the presence of fossils of adult australopithecines of different sizes as representing a relatively large degree of sexual dimorphism. On the other hand, others conclude that the two collections of bone represent two distinct species, a smaller and a larger one.

The determination of sex based upon a fossilized pelvis is difficult. The secondary sexual characteristics that distinguish the modern male and female pelvis are very well known. However, it may not be correct to expect the same features to differentiate sex in australopithecine material.

Another approach taken by the investigators was to determine the size of the head of the fetus and then to see if it could fit through the birth canal. Based on this analysis they conclude that Lucy was actually a male. If this is true, then two distinct species, a large and a small one, must exist. On the other hand, many paleoanthropologists criticize this analysis because of all the assumptions that have to be made when dealing with disputed reconstruction of the pelvis and with the method and data used to estimate the size of the fetal head.

1 S. R. Loth, M. Henneberg, and J. F. Thackeray, "Assessment of the sex of Sts 5 and Stw 53: A New Consideration of Sexual Dimorphism in Fossil Hominids," American Journal of Physical Anthropology, Supplement 20 (1995), 136-137; B. Bower, "Hominid Skull Gets Abrupt Sex Change," Science News, 147 (April 8, 1995), 215.

2 M. Hüsler and P. Schmid, "Comparison of the Pelves of STS 14 and AL 299-1: Implications for Birth and Sexual Dimorphism in Australopithecines," Journal of Human Evolution, 29 (1995), 363-383.