Molecular biology and evolution.
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Fig. 1.—The first members of early Homo sapiens are really quite distinct from their australopithecine predecessors and contemporaries. Perhaps the most fundamental dissimilarity, a dramatic size difference, is shown here in this correctly scaled comparison of the reconstructed skeletons of two women: "Lucy," a 3-Myr-old australopithecine (Wood 1992{Citation} ), and ER 1808 (Walker, Zimmerman, and Leakey 1982{Citation} ), a woman of our species about half that age. Australopithecine contemporaries to ER 1808 were as small as Lucy. Other differences lie in skeletal proportions and brain size (fig. 2 ), both absolute and relative to body size.
- We, like many others, interpret the anatomical evidence to show that early H. sapiens was significantly and dramatically different from earlier and penecontemporary australopithecines in virtually every element of its skeleton (fig. 1 ) and every remnant of its behavior (Gamble 1994 ; Wolpoff and Caspari 1997 ; Asfaw et al.
- ult, with a broad frontal bone and an expanded parietal association area; neural canal expansion); (2) changing dental function (more anterior tooth use, greater emphasis on grinding and less on crunching) as reflected in broader faces and larger nuchal areas; (3) development of a cranial buttressing system to strengthen the vault, including vault bone thickening and prominent tori; and (4) dramatic expansion of body height (estimated average weights double) and numerous changes in proportions (fig. 1 ).
Molecular biology and evolution.
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Fig. 2.—Plot of mean log10 brain weights and body weights for 85 living primate species (Holloway 1988{Citation} ). Two early hominids complete enough for estimates of brain and body weight are inserted in position: the Hadar australopithecine female AL 288-1 ("Lucy") and the early Homo sapiens Turkana boy ER 15000 (adult estimates for the parameters are plotted). Note that the australopithecine is within the nonhuman primate distribution, while ER 15000 is beyond their ellipsoid of variation and is like the human above it (the figurine represents the population means for living H. sapiens). The gorilla value (the largest body size for any living primate) is also shown as a figurine. These and other data show that cranial capacity in living and fossil H. sapiens is beyond the expectations of primate allometry. This expansion is the case only for H. sapiens, even the earliest, and it is one of the most dramatic and important distinctions of the species.
- The significant change to the cranial size of H. sapiens is greater than could be explained by body size alone (fig. 2 ), which also greatly increases as discussed below.
- Other differences lie in skeletal proportions and brain size (fig. 2 ), both absolute and relative to body size.
Molecular biology and evolution.
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Fig. 3.—Comparison of the Stw 431 australopithecine (left) and KNM-ER 3228 early H. sapiens male innominates (drawings by Karen Harvey). ER 3228, dated at 1.95 ± 0.05 Myr, is the earliest specimen that can unquestionably be attributed to the earliest known direct ancestor of living human populations in the genus Homo. The Sterkfontein innominate is at least 200,000 years older (Schwarcz, Grün, and Tobias 1994{Citation} ).
- It differs from them in features such as the relatively large acetabulum and strongly developed iliac pillar (fig. 3 ).
- figure 3 shows the basis for this interpretation, with the earliest known specimen of H. sapiens, the male innominate discussed above.
- We thank Karen Harvey for kindly providing the drawing of innominates in figure 3 , the National Museums of Kenya for permission to study the fossil specimens reported on here, and the National Science Foundation for its support.
Molecular biology and evolution.
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Fig. 4.—Frequency distribution of Late Pliocene and Early Pleistocene (approximately 1.9–1.6 Myr) Koobi Fora femur lengths in centimeters, actual or as estimated by McHenry (1991){Citation} and Ruff and Walker (1993){Citation} . The total range exceeds the variation in Africa today, where the world’s shortest and tallest populations are found. The larger mode is the size of very tall populations such as Tutsi or Nuer, and the middle mode is approximately Khoisan-sized. All specimens associated with crania in the large group are attributed to early H. sapiens (both sexes are represented), and all associated specimens in the small group are australopithecines. There are no cranial associations for the femora in the middle-sized group, but the oft-made suggestion that they represent the larger habiline species (or sex) is not unreasonable. The middle group are not likely to be females of early H. sapiens, because the only demonstrable female, KNM-ER 1808, is in the large group. This distribution indicates that early H. sapiens was quite large and had a human-like magnitude of sexual dimorphism in body size.
- The frequency distribution for femur length (fig. 4 ) shows this quite unequivocally.
Molecular biology and evolution.
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Fig. 5.—Distribution of coalescence estimates for mtDNA, arranged in order of publication date. Methods of range estimation vary; see specific sources for details. It would be fair to say that the uncertainty of this information has been increasing over time (and for further uncertainty see Parsons and Holland [1998]{Citation} ).
- A wide range of estimates was obtained (fig. 5 ); 200,000 years is a widely accepted median estimate.
Molecular biology and evolution.
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Fig. 1.—Phylogeny of diverse eukaryotes based on beta-tubulin; BioNJ tree of maximum-likelihood (ML) distances corrected for site-to-site rate variation. Numbers at selected nodes indicate support greater than 50% from neighbor-joining of gamma-corrected ML distance bootstraps (top) and percentage of occurrence in the quartet puzzling tree (bottom).
- In trees constructed with a variety of eukaryotes plus the fungal and microsporidian sequences reported here, the same overall relationships are recovered with support values similar to or slightly lower than those reported in published analyses (fig. 1 ).
- In contrast to figure 1 , the four fungal divisions are monophyletic in this tree (with the single exception of the divergent Spizellomyces 2 gene), and their branching order reflects the expected pattern, with chytrids branching first, followed by zygomycetes and, finally, basidiomycetes and ascomycetes (Bruns et al.
- As with the larger analysis shown in figure 1 , many of the surprisingly poorly supported features were found to be affected by the more divergent sequences (especially Linderina), so once again, trees were inferred using only the most conserved representatives of each of the four fungal divisions (fig. 2 B and C).
Molecular biology and evolution.
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Fig. 2.—Phylogeny of microsporidian and fungal beta-tubulins with animals as the outgroup; BioNJ trees of maximum-likelihood (ML) distances corrected for site-to-site rate variation. A, Diverse fungi and microsporidia represented. Numbers at selected nodes refer to support greater than 50% from (top to bottom) neighbor-joining of gamma-corrected ML distance bootstraps, and percentage of occurrence in the quartet puzzling tree. B and C, Phylogeny of beta-tubulins from microsporidia and the most conserved representatives of the four fungal divisions, excluding Conidiobolus (B) and including Conidiobolus (C). Numbers at selected nodes indicate support greater than 50% from (top to bottom) neighbor-joining of gamma-corrected ML distance bootstraps, ML resampling estimated log likelihood (RELL) bootstraps from quick-add search, and percentage of occurrence in the quartet puzzling tree. Other distance bootstrapping scores were similar to those shown, and relative likelihood support scores were similar to RELL bootstraps, so for clarity, only representatives are shown.
- To allow more comprehensive analyses and to exclude the potential effects of distant outgroups, the branching order between fungi and microsporidia was further examined using only animals as an outgroup. figure 2 A shows a tree including the same selection of fungal tubulins with an animal outgroup.
- As with the larger analysis shown in figure 1 , many of the surprisingly poorly supported features were found to be affected by the more divergent sequences (especially Linderina), so once again, trees were inferred using only the most conserved representatives of each of the four fungal divisions (fig. 2 B and C).
- When Conidiobolus was excluded, the microsporidia branched with the ascomycetes (fig. 2 B), but when it was included, the microsporidia branched specifically with Conidiobolus, and zygomycetes were paraphyletic (fig. 2 C).
- A potentially analogous situation is seen for ascomycetes, in which several divergent yeast beta-tubulins cluster together beneath the archeoascomycete, Pneumocystis (fig. 2 A).
- Indeed, microsporidian polar tube eversion is also reminiscent of spore dispersion in Conidiobolus (Ingold 1971 ), and Conidiobolus branches with microsporidia in some analyses of beta-tubulin (fig. 2 C).
Molecular biology and evolution.
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Fig. 3.—Phylogenetic relationships between (A) beta-tubulin and (B) alpha-tubulin from microsporidia and chytrid fungi, with diplomonads as the outgroup; BioNJ trees of maximum-likelihood (ML) distances corrected for site-to-site rate variation. Numbers at selected nodes indicate support greater than 50% from gamma-corrected neighbor-joining bootstraps (top) and percentage of occurrence in the quartet puzzling tree (bottom). Alternative positions for microsporidia were assessed with the Kishino-Hasegawa test at nodes with circles. In both trees, the fungal position was preferred, while nodes with open circles were not rejected at confidence levels of 90% and nodes with closed circles were rejected (at confidence levels over 90% for beta-tubulin and over 95% for alpha-tubulin).
- In such an analysis of beta-tubulins from a wide variety of eukaryotes, the latter result is found (fig. 3 A), suggesting that the relationship between microsporidian and fungal beta-tubulins is indeed genuine.
- The position of the microsporidia with the chytrid fungi was also compared directly with six alternative positions by Kishino-Hasegawa tests (fig. 3 A).
- As with beta-tubulin, the microsporidian and chytrid fungal alpha-tubulins retain a specific relationship in alpha-tubulin phylogeny despite an even greater disparity in evolutionary rates (fig. 3 B).
- The new data from chytrid fungi argue against long-branch attraction being solely responsible for the placement of microsporidia with fungi (fig. 3 ).
Molecular biology and evolution.
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Fig. 1.—Two parsimonious pathways between codons TTA and CTC. Probabilities are calculated using parameter estimates for the human and orangutan mitochondrial genes.
- An example is given in Figure 1 using a pair of codons in the mitochondrial genes of the human and the orangutan.
- Transition probabilities for changes involved in each of the two pathways are given in Figure 1 , calculated using the estimates obtained by the new method (t = 0.873, = 10.61, and = 0.057).