Size variation and sexual dimorphism in Australopithecus afarensis and living hominoids
Size variation and sexual dimorphism in Australopithecus afarensis and living hominoids
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南方古猿阿法种和现生类人猿的体型变异和性别二态性
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发表时间：
1995
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通讯作者：
W. Jungers
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作者：
B. Richmond;W. Jungers
摘要埃塞俄比亚上新世发现的新化石归属于南方古猿阿法种（白色等人，1993; Kimbel等人，1994）提供了一个机会，重新评估这些早期原始人类的颌骨和四肢骨的大小变化和性别二型性。在这项研究中，两个相关的问题是解决使用精确的随机化方法。首先，是否有可能在现代人科动物的样本中观察到化石的大小范围？第二，从最小/最大可能性到概率，在现存的类人猿中取样这种差异的可能性有多大？化石尺寸和形状的最小/最大范围由下颌骨样本A.L. 444-2b与A.L. 207- 1/3、肱骨MAK-VP-1/3与A.L. 288-lm以及近端股骨A.L. 333-3与A.L. 288-lap的线性测量值确定。现代的参考样本包括大猩猩、猩猩、普通黑猩猩和几个人类群体（都是已知性别的）。在每个样本中计算所有可能的成对对比（在大小比和平均欧几里得距离中）[例如，在50只大猩猩（25只雄性，25只雌性）的样本中，1225个总对比是可能的，其中625个是异性对比]，并注意到找到与化石对中所见差异一样大的差异的概率。在人类和黑猩猩样本中，下颌骨、肱骨和股骨近端化石的最大观察到的尺寸（性别）差异要么罕见，要么没有观察到，在猩猩中是罕见的，甚至在大猩猩中也是不寻常的。将来发现的标本无疑会增加化石的分布范围，从而进一步减少现代分类群中匹配这种差异的可能性。这些结果可能意味着多个类群存在于化石组合。如果把来自Hadar和Maka（以及Laetoli）的化石假定为来自一个两性异形种，那么A.阿法病至少与现存的最具二态性的猿类（大猩猩和猩猩）一样极端。因此，严格的一夫一妻制社会结构是极不可能的。
Abstract New fossils recovered from the Pliocene of Ethiopia and attributed to Australopithecus afarensis (White et al., 1993; Kimbel et al., 1994) provide an opportunity to reassess size variation and sexual dimorphism in jaws and limb bones of these early hominids. In this study two related questions are addressed using exact randomization methods. First, is it possible to observe the fossil size range within samples of modern hominoids? Second, and moving beyond minimum/maximum possibilities to probabilities , what is the likelihood of sampling such differences in extant hominoids? Fossil minimum/maximum ranges in size and shape are defined by linear measurements from mandibular specimens A.L. 444-2b vs. A.L. 207-13, humeri MAK-VP-1/3 vs. A.L. 288-lm, and the proximal femora A.L. 333-3 vs. A.L. 288-lap. Modern reference samples include gorillas, orang-utans, common chimpanzees and several human groups (all of known sex). All possible pairwise contrasts (in size ratios and average Euclidean distances) are computed within each sample [e.g. within a sample of 50 gorillas (25 males, 25 females) 1225 total contrasts are possible of which 625 are opposite sex contrasts], and the probability of finding a difference as great as that seen in the fossil pair is noted. The maximum observed size (sex) difference in the fossil mandibles, humeri and proximal femora is either rare or not observed in human and chimpanzee samples, is rare to uncommon in orang-utans, and is unusual even in gorillas. Specimens recovered in the future will undoubtedly increase the fossil ranges, and thereby further reduce the probabilities of matching such differences in modern taxa. These results could imply that multiple taxa exist within the fossil assemblage. If the fossils from Hadar and Maka (and Laetoli) are assumed instead to be from one sexually dimorphic species, then the degree of sexual dimorphism of A. afarensis would have been at least as extreme as that of the most dimorphic living apes, the gorilla and orang-utan. It follows that a strictly monogamous social structure would have been highly unlikely.