Abstract:This contribution reviews the evidence that has resolved the branching structure of the higher primate part of the tree of life and the substantial body of fossil evidence for human evolution. It considers some of the problems faced by those who try to interpret the taxonomy and systematics of the human fossil record. How do you to tell an early human taxon from one in a closely related clade? How do you determine the number of taxa represented in the human clade? How can homoplasy be recognized and factored i… Show more
“…Anthropologists continue to debate the phylogenetic relationships among fossil taxa representing our ancestors and cousins (34), but genetic evidence unequivocally corroborates Darwin's hypothesis about our African ape ancestry (35). The genera ancestral to our own are often characterized as bipedal apes (36), and chimpanzees are commonly used as a living model for the ancestors of our genus because they are genetically closest to us and similar in body and brain size to these extinct taxa (37).…”
In the first paper to present formal theory explaining that senescence is a consequence of natural selection, W. D. Hamilton concluded that human postmenopausal longevity results from the contributions of ancestral grandmothers to the reproduction of their relatives. A grandmother hypothesis, subsequently elaborated with additional lines of evidence, helps explain both exceptional longevity and additional features of life history that distinguish humans from the other great apes. However, some of the variation observed in aging rates seems inconsistent with the tradeoffs between current and future reproduction identified by theory. In humans and chimpanzees, our nearest living relatives, individuals who bear offspring at faster rates do not cease bearing sooner. They continue to be fertile longer instead. Furthermore, within both species, groups with lower overall mortality rates have faster rates of increase in death risk with advancing age. These apparent contradictions to the expected life history tradeoffs likely result from heterogeneity in frailty among individuals. Whereas robust and frail alike must allocate investments between current and future reproduction, the more robust can afford more of both. This heterogeneity, combined with evolutionary tradeoffs and the key role of ancestral grandmothers they identify, helps explain aspects of human aging that increasingly concern us all.evolution of senescence | heterogeneity of frailty | human life history | menopause | human aging L ong postmenopausal survival is a characteristic of our species.
“…Anthropologists continue to debate the phylogenetic relationships among fossil taxa representing our ancestors and cousins (34), but genetic evidence unequivocally corroborates Darwin's hypothesis about our African ape ancestry (35). The genera ancestral to our own are often characterized as bipedal apes (36), and chimpanzees are commonly used as a living model for the ancestors of our genus because they are genetically closest to us and similar in body and brain size to these extinct taxa (37).…”
In the first paper to present formal theory explaining that senescence is a consequence of natural selection, W. D. Hamilton concluded that human postmenopausal longevity results from the contributions of ancestral grandmothers to the reproduction of their relatives. A grandmother hypothesis, subsequently elaborated with additional lines of evidence, helps explain both exceptional longevity and additional features of life history that distinguish humans from the other great apes. However, some of the variation observed in aging rates seems inconsistent with the tradeoffs between current and future reproduction identified by theory. In humans and chimpanzees, our nearest living relatives, individuals who bear offspring at faster rates do not cease bearing sooner. They continue to be fertile longer instead. Furthermore, within both species, groups with lower overall mortality rates have faster rates of increase in death risk with advancing age. These apparent contradictions to the expected life history tradeoffs likely result from heterogeneity in frailty among individuals. Whereas robust and frail alike must allocate investments between current and future reproduction, the more robust can afford more of both. This heterogeneity, combined with evolutionary tradeoffs and the key role of ancestral grandmothers they identify, helps explain aspects of human aging that increasingly concern us all.evolution of senescence | heterogeneity of frailty | human life history | menopause | human aging L ong postmenopausal survival is a characteristic of our species.
“…The speciation time between human and chimpanzee was estimated to be 5.9–7.6 Ma in our analysis, which is consistent with both the most recent findings obtained using a genomic approach (Scally et al 2012) and the traditional view from fossil records (Carroll 2003). Orrorin (∼6 Ma) (Wood 2010) and Sahelanthropus (∼7 Ma) (Brunet et al 2005) both lived around the time of human–chimpanzee speciation. In contrast, Ardipithecus was considered to emerge after this speciation, with Ar.…”
Section: Discussionmentioning
confidence: 99%
“…F ig . 3.—Relationship between the estimated speciation times and the fossil records of ancestral great apes (Sawada et al 1998; Ishida et al 1999; Gabunia et al 2001; Haile-Selassie 2001; Brunet et al 2005; Kunimatsu et al 2007; Suwa et al 2007; Wood 2010), for details see Discussion. Dotted lines represent the upper and lower bounds of the 95th percentiles of estimated speciation times (orange for THC and purple for THCG) (table 3) .…”
The demographic history of human would provide helpful information for identifying the evolutionary events that shaped the humanity but remains controversial even in the genomic era. To settle the controversies, we inferred the speciation times (T) and ancestral population sizes (N) in the lineage leading to human and great apes based on whole-genome alignment. A coalescence simulation determined the sizes of alignment blocks and intervals between them required to obtain recombination-free blocks with a high frequency. This simulation revealed that the size of the block strongly affects the parameter inference, indicating that recombination is an important factor for achieving optimum parameter inference. From the whole genome alignments (1.9 giga-bases) of human (H), chimpanzee (C), gorilla (G), and orangutan, 100-bp alignment blocks separated by ≥5-kb intervals were sampled and subjected to estimate τ = μT and θ = 4μgN using the Markov chain Monte Carlo method, where μ is the mutation rate and g is the generation time. Although the estimated τHC differed across chromosomes, τHC and τHCG were strongly correlated across chromosomes, indicating that variation in τ is subject to variation in μ, rather than T, and thus, all chromosomes share a single speciation time. Subsequently, we estimated Ts of the human lineage from chimpanzee, gorilla, and orangutan to be 6.0–7.6, 7.6–9.7, and 15–19 Ma, respectively, assuming variable μ across lineages and chromosomes. These speciation times were consistent with the fossil records. We conclude that the speciation times in our recombination-free analysis would be conclusive and the speciation between human and chimpanzee was a single event.
“…ramidus, Australopithecus spp., Paranthropus spp., and Homo spp.) (Wood, 2010), while other hominoids are nearly absent in the African fossil record of this period, except for a few isolated teeth discovered from the Tugen Hills in Kenya (~0.5 Ma) and assinged to Pan sp. (McBreaty and Jablonski, 2005).…”
Nakali is an early Late Miocene fossil locality in north-central Kenya, where the KenyaJapan Joint Expedition team has carried out fieldwork since 2002. Previously, a large hominoid Nakalipithecus nakayamai was reported from site NA39 of this locality. In addition to Nakalipithecus, the hominoid material collected from Nakali includes an isolated P 3 , which shows a considerably different morphology from the P 3 assigned to Nakalipithecus, suggesting the presence of a different hominoid species. The general morphology of this P 3 is reminiscent of that of primitive hominoids such as Proconsul, which are mainly known from the Early Miocene of East Africa. Although the present material is limited, the presence of a primitive-looking second hominoid species in Nakali indicates a higher hominoid (and hominoid-like catarrhine) diversity in the early Late Miocene of Africa than previously envisaged.
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