In the Light of Evolution Volume IV: The Human Condition (2010) / Chapter Skim
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2 Terrestrial Apes and Phylogenetic Trees--Juan Luis Arsuaga
2 Terrestrial Apes and Phylogenetic Trees--Juan Luis Arsuaga
Pages 27-46
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From page 27... ...
paid little attention to the only human fossils known at the time that were not modern humans, the neanderthals. only two references to them can be found in its pages, Centro (Universidad Complutense de Madrid–instituto de salud Carlos iii)
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From page 28... ...
. The reason behind Darwin's lack of interest in the neanderthals may stem from the judgment made previously of these same specimens by Thomas henry huxley in his Evidence as to Man's Place in Nature in 1863: "the neanderthal cranium is by no means so isolated as it appears to be at first, but forms, in reality, the extreme term of a series leading gradually from it to the highest and best developed of human crania." Darwin was in search of a "missing link," a transitional form between modern humans and the chimpanzee or gorilla.
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From page 29... ...
: "it is quite certain that the Ape which most nearly approaches man, in the totality of its organization, is either the Chimpanzee or the Gorilla." nevertheless, this did not lead huxley to group us in the same taxonomic category with the African apes. rather, it was they who were grouped with the other great ape, the orangutan, along with the lesser apes, the gibbons, in the same category: "The structural differences between Man and the Man-like apes certainly justify our regarding him as constituting a family apart from them." The only way that modern humans are included within the group of apes, in which we are considered apes, is if we are more closely related phylogenetically to some of them (the African apes)
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From page 30... ...
, he writes: "We can understand why a species of a group of species may depart, in several of its most important characteristics, from its allies, and yet be classed with them." nevertheless, Darwin does not seem to have recognized our common origin with the African apes because he drew, on April 21 in 1868, a sche matic genealogical tree of the primates (Fig.
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From page 31... ...
surprisingly, the gibbons were initially placed as the closest to humans, with the African apes further removed. These respective positions were subsequently changed so that the chimpanzee and gorilla are closer to humans, although they do not share a common ancestor with us.
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From page 32... ...
That modern humans shared some derived features only with African apes (but not the orangutans) was not realized at the time by le Gros Clark.
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From page 33... ...
The third pattern was the cause of large-scale changes in the adaptive types (biological designs or body plans) that were produced in relatively short periods of geological time and that gave rise to large evolutionary novelties in the highest-level taxonomic categories.
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From page 34... ...
occurred directly and only once or whether a transitional form had previously existed with a generally primitive skeleton but with some particular key feature (perhaps in the iliac blade as suggested by Washburn) that made an early form of facultative bipedal locomotion, still compatible with some degree of life in the trees, possible.
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From page 35... ...
According to the researchers who described the specimen, some features characteristic of the modern human pelvis that are strongly related to bipedal posture -- because they permit abduction during walking -- can already be appreciated and are also found in the australopithecines and later hominids: a short iliac isthmus, a slightly broadened and sagittally oriented ilium with a weak greater sciatic notch, and a strong, anterior inferior iliac spine formed by a separate ossification center. in addition, the pubic symphysis would have been superoinferiorly short, differing from the tall symphysis in chimpanzees.
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From page 36... ...
fairly convincing demonstration that two species of australopithecines may have lived in south Africa within a relatively short period of time, if not simultaneously, this hypothesis remains now probable only for the representatives of the genus Homo." For Dobzhansky, anagenesis predominated over cladogenesis in human evolution: "Both cladogenetic and anagenetic changes took place in man's ancestry but the latter predominated. Mankind was and is a single inclusive Mendelian population and is endowed with a single, corporate geno type, a single gene pool." Whether or not the evolution of the genus Homo represents a single lineage (i.e., a single panmictic unit)
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From page 37... ...
Terrestrial Apes and Phylogenetic Trees / FiGUre 2.2 Changes in body shape in Homo (Carretero et al., 2004)
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From page 38... ...
in reality, however, postcranial remains are abundant only at the Middle Pleistocene site of the sima de los huesos in the sierra de Atapuerca, dated to at least 530 kya. nevertheless, the isolated fossils from other sites such as the east African pelvises KnM-er 3228 (perhaps older than the Turkana Boy)
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From page 39... ...
erectus fossils from ngandong (Java) have cranial capacities similar to that of Cranium 5 from the sima de los huesos but the neurocranial anatomy is very different.
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From page 40... ...
if in the late Pleistocene, when the fossil record is more complete, we find that four different human lineages coexisted, why not think that this has been the general trend? it is important to point out here that, although this encephalization can be represented as a curve, it does not necessarily imply a steady, continuous rate of increase through time.
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From page 41... ...
. if, on the other hand, the species Homo neanderthalensis is accepted, their last ancestor could still be H
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From page 42... ...
. The problem is that many researchers have recognized derived neanderthal features, developed to a greater or a lesser degree, in the european middle Middle Pleistocene fossils, including the Mauer mandible, but not in the African specimens.
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From page 43... ...
. The fossils from the sima de los huesos are neither phenetically nor cladistically H
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From page 44... ...
erectus) nor apomorphies of neanderthals and modern humans, but intermediate character states that could give rise to one or the other.
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From page 45... ...
in principle, autapomorphies have not been found in the sima de los huesos, which would exclude them from forming part of a chronospecies in the evolution of the neanderthals, but this is because the unique features that are found (in this and other european middle Middle Pleistocene fossils) are interpreted as character states that are intermediate in their polarity.
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From page 46... ...
as occurred in the sima de los huesos and happens in any living human population, even across the entire species. if this is correct, and we may know when there are additional samples discovered, we would have other "enti ties" like the sima de los huesos.
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