Hominin fossil evidence in the Turkana Basin in Kenya from ca . 4.1 to 1.4 Ma samples two archaic early hominin genera and records some of the early evolutionary history of Paranthropus and Homo . Stable carbon isotopes in fossil tooth enamel are used to estimate the fraction of diet derived from C 3 or C 4 resources in these hominin taxa. The earliest hominin species in the Turkana Basin, Australopithecus anamensis , derived nearly all of its diet from C 3 resources. Subsequently, by ca . 3.3 Ma, the later Kenyanthropus platyops had a very wide dietary range—from virtually a purely C 3 resource-based diet to one dominated by C 4 resources. By ca . 2 Ma, hominins in the Turkana Basin had split into two distinct groups: specimens attributable to the genus Homo provide evidence for a diet with a ca . 65/35 ratio of C 3 - to C 4 -based resources, whereas P. boisei had a higher fraction of C 4 -based diet ( ca . 25/75 ratio). Homo sp. increased the fraction of C 4 -based resources in the diet through ca . 1.5 Ma, whereas P. boisei maintained its high dependency on C 4 -derived resources.
The most complete early hominid skeleton ever found was discovered at Nariokotome III, west Lake Turkana, Kenya, and excavated in situ in sediments dated close to 1.6 Myr. The specimen, KNM-WT 15000, is a male Homo erectus that died at 12 +/- 1 years of age, as judged by human standards, but was already 1.68 m tall. Although human-like in many respects, this specimen documents important anatomical differences between H. erectus and modern humans for the first time.
A combined population genetic and reproductive analysis was undertaken to compare free-ranging cheetahs from east Africa (Acinonyxjubatus raineyi) with the genetically impoverished and reproductively impaired south African subspecies (Acinonyx jubatus jubatus). Like that of their south African counterparts, the quality of semen specimens from east African cheetahs was poor, with a low concentration of spermatozoa (25.3 x 106 per ejaculate) and a high incidence of morphological abnormalities (79%). From an electrophoretic survey of the products of 49 genetic loci in A. jubatus raineyi, two allozyme polymorphisms were detected; one of these, for a nonspecific esterase, shows an allele that is rare (less than 1% incidence) in south African specimens. Estimates ofpolymorphism (24%) and average heterozygosity (0.0004-0.014) affirm the cheetah as the least genetically variable felid species. The genetic distance between south and east African cheetahs was low (0.004), suggesting that the development of genetic uniformity preceded the recent geographic isolation of the subspecies. We propose that at least two population bottlenecks followed by inbreeding produced the modern cheetah species. The first and most extreme was ancient, possibly late Pleistocene (circa 10,000 years ago); the second was more recent (within the last century) and led to the south African populations.Modern cheetah populations, which number less than 20,000 animals, are largely restricted to two zoogeographic subspecies: Acinonyx jubatus jubatus (range including portions of South Africa, Namibia, Mozambique, and Zambia) and the east-central African subspecies, Acinonyx jubatus raineyi (found in Kenya, Tanzania, Uganda, and some central African countries) (1-6). We recently discovered that the south African cheetah (A. jubatus ubatus) is unique among felids and other mammals in having an extreme paucity of genetic variation as estimated by electrophoretic surveys of allozymes and cell proteins resolved by two-dimensional gels (7). More unusual was the observation ofallogeneic slain graft acceptance among unrelated cheetahs, revealing genetic monomorphism at the major histocompatibility complex, an abundantly polymorphic locus in nearly all mammals (8).Captive reproduction of cheetahs historically has been poor and their infant mortality rate is high (8). A comparative analysis of cheetah ejaculates revealed a sperm count 1/10th of that observed in domestic cats and an extremely high frequency (71%) of morphological spermatozoal abnormalities (9, 10). In addition to these phenotypic observations, patterns of skeletal variation also show significant asymmetry of bilateral characters, a phenomenon generally common in inbred animals (11,12). The combined genetic, reproductive, and morphological data placed the cheetah in a status reminiscent of deliberately inbred mice or livestock and prompted us to hypothesize that in its recent history the species had probably suffered a demographic contraction or population bottleneck necessarily followed ...
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