Size and scaling in human evolution

Our general conclusion is simply stated: many lineages display phyletic size increase; allometric changes almost always accompany increase in body size. We cannot judge adaptation until we separate such changes into those required by increasing size and those serving as special adaptations to changing environments. In our view, the three australopithecines are, in a number of features, scaled variants of the "same" animal. In these characters, A. africanus is no more "advanced" than the larger, more robust forms. The one early hominid to show a significant departure from this adaptive pattern toward later hominids-cranially, dentally, and postcranially-is H. habilis from East Africa. The australopithecines, one of which was probably a precursor of the Homolineage, were apparently a successful group of basically vegetarian hominids, more advanced behaviorally than apes (87), but not hunter-gatherers. The fossil hominids of Africa fall into two major groupings. One probable lineage, the australopithecines, apparently became extinct without issue; the other evolved to modern man. Both groups displayed steady increase in body size. We consider quantitatively two key characters of the hominid skull: cranial capacity and cheek tooth size. The variables are allometrically related to body size in both lineages. In australopithecines, the manner of relative growth neatly meets the predictions for functional equivalence over a wide range of sizes (negative allometry of cranial capacity with a slope against body weight of 0.2 to 0.4 and positive allometry of postcanine area with a slope near 0.75). In the A. africanus to H. sapiens lineage, cranial capacity increases with positive allometry (slope 1.73) while cheek teeth decrease absolutely (slope - 0.725). Clearly, these are special adaptations unrelated to the physical requirements of increasing body size. We examined qualitatively other features, which also seem to vary allometrically. Of course, many characters should be studied quantitatively, but we think that the scheme outlined here should be treated as the null hypothesis to be disproved.     

Susceptibility of the gibbon Hylobates lar to falciparum malaria

The splenectomnized juvenile gibbon, Hylobates lar, is susceptible to infection with trophozoites of Plasmodium falciparum. All subjects in a group of six animals that were injected with freshly collected blood from four infected humans in Saraburi Province, Thailand, developed parasitemia 2 to 20 days later; infections were transmitted from one of these subjects to three clean gibbons.     

Habitat characterization of Texas wild‐rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River,TX, USA

1. The habitat of Texas wild‐rice (Zizania texana Hitchcock), known only from the spring‐fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild‐rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα_0.05=0.60; p=0.009), but even non‐significant levels of turbidity may present biologically significant impacts to wild‐rice plants. 3. Differences in substrate particle size were highly significant (Kα_0.05=0.71; p=0.001) with Texas wild‐rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non‐rice sites (82%). However, no significant differences were found in organic matter content among rice and non‐rice transects ( =2.09 and 2.56%, respectively). 4. Texas wild‐rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non‐rice sites ( ≥0.46 m s⁻¹ and ≤0.22 m s⁻¹, respectively). 5. Texas wild‐rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild‐rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild‐rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd.