Paleoantropología y estudios sobre lo humano, epistemología de las ciencias de la vida y el juego de los conceptos
Cristian R. Altaba
The conundrum of hominid systematics
Palabras clave / Keywords: semántica, lenguaje, homínido
A review of the systematics and taxonomy of hominoidea: history, morphology, molecules, and fossils (Pág. 15-45)
Jeffrey H. Schwartz
The history of hominoid systematics reveals a general tendency to recognize diversity in the fossil record of “apes” and “basal hominoids,” but a view toward taxonomic limitation with regard to hominids, which was exacerbated in the 1980s by the “removal” of fossils such as Sivapithecus (=Ramapithecus) and their association via morphological synapomorphy with Pongo. The latter, in turn, reinforced the increasingly accepted, molecularly based theory of human-African ape relatedness, which was never substantially supported by morphology. Although claims to being cladistic in associating humans with the African apes (or Pan alone) abound in the literature, molecularly and morphologically based analyses are, however, not only procedurally different, they identify synapomorphy differently. Continuing confusion of orangutan-like specimens as hominids plus recent re-evaluations of diversity in the human fossil record as well new discoveries of so-called basal fossil hominoids argue for a broadening of hominoid classification until such time as the clades and the relationships between and within them become better understood.
Palabras clave / Keywords: systematics, hominoid, hominid, synapomorphy, orangutan clade, molecules versus morphology, regulatory genes.
An objective time based phylogenetic classification of primates that places chimpanzees and humans in the genus Homo (Pág. 47-62)
Molecular phylogenetics, a coupling of molecular biology to Hennig’s phylogenetic systematics, is bringing about a twofold shift in paradigms, one in systematics and the other in how we view our place in nature. The new paradigm in systematics disbands the traditional use of taxonomic grades and, instead, favors strictly genealogical classifications in which all taxa are monophyletic and are arranged in a hierarchical scheme that reflects the time course of phylogeny. The second new paradigm rejects the traditional anthropological view that we humans are greatly different from all other species and instead emphasizes our commonalities with other species, e.g. our very close genetic identity to chimpanzees. On using DNA evidence on primate phylogeny, complemented by paleontological evidence, a temporal based classification of primates describes objectively, without anthropocentric biases, the taxonomic place of humans among the primates. All living apes and humans belong to subfamily Homininae. Homininae divides into Hylobatini (common and siamang gibbons) and Hominini, the latter into Pongina for Pongo (orangutans) and Hominina for Gorilla and Homo. Homo itself divides into the subgenera H. (Homo) for humans and H. (Pan) for common and pygmy chimpanzees. Even on disbanding Australopithecus and Ardipithecus by placing their species into Homo (Homo), the presumed genealogical relationships of these extinct species to each other and to living humans can be depicted by how the species are listed and indented under the subgenus rank.
Palabras clave / Keywords: molecular phylogenetics, phylogenetic classification, taxonomic ranks, DNA evidence, primate phylogeny, primate clades, bipedal hominids, common and bonobo chimpanzees, Homo (Homo), Homo (Pan).
Bernard Wood, Mark Collard
The taxonomic history of the genus Homo, up to the inclusion of Homo habilis and Homo rudolfensis, is reviewed. The two main contemporary interpretations of the genus concept, that differ according to whether information about grade is used, and in the way a clade is interpreted, are presented. It is suggested that neither of these definitions is satisfactory, and a new definition, that a genus should be ‘a species, or monophylum whose members occupy a single adaptive zone’, is offered. For a newly discovered, or newly recognized, taxon to be included within an existing genus two criteria are suggested. First, the candidate species should belong to the same monophyletic group as the type species of the proposed genus. Second, the adaptive strategy of the candidate species should be closer to the adaptive strategy of the type species of the proposed genus than it is to the type species of any other genus. When applied to the taxa presently subsumed within Homo two taxa, H. habilis and H. rudolfensis, fail the tests. It is suggested that at least one new genus, and probably two new genera, are needed to accommodate the taxa excluded from Homo.
Palabras clave / Keywords: genus, Homo, grade, clade, Homo habilis, Homo rudolfensis, phylogenetic analysis, language, tool-making.
Milford H. Wolpoff
Hypotheses of species genealogy are poorly supported when the species are closely related, and phylogenetics cannot be justified at all below the species level both for this reason and because the parsimony principle is invalid when there is reticulation. With the transfer of the habiline species out of Homo, several lines of evidence suggest that this genus has only a single lineage and therefore a species throughout the Pleistocene: Homo sapiens. Anatomical details supporting this contention are found in the continuity of different features in different regions. The emerging pattern shows population reticulation based on gene flow and population movement that reflects a network of interrelationships allowing adaptive changes to broadly spread throughout the species range. Genetic evidence precludes a recent small population size bottleneck, and thereby makes very unlikely an explanation of Pleistocene variation and evolution based on successive species replacements. Multiregional evolution remains both well supported and not refuted by these data, and this implies that Pleistocene human evolution and relationships must be studied without a taxonomic framework.
Palabras clave / Keywords: Tt1xonomy, phylogeny, species, evolutionary trees, multiregional evolution.
Camilo J. Cela-Conde
A bottom-up way is a means of reaching knowledge, starting at the bottom level of raw data, and arriving at the top level of a more general description. Several authors—such as Delson, Eldredge and Tattersall (1977), Skelton, McHenry and Drawhorn (1986), and Strait, Grine and Moniz (1997)— attempt to use bottom-up methodologies in the paleontological field. However, if problems like those of trait biases must be avoided, it seems difficult to disregard functional criteria when constructing cladograms. Since functional criteria works on a top-down way—starting at a higher level of knowledge we deduce a lower conclusion—the naïve aim of constructing phylogenies in an extreme bottom-up way ends up by being hard to reach.
Palabras clave / Keywords: cladogram, falsification, phylogeny, bottom-up knowledge, hypodigm, parsimony scenario, phylogeny, species, ancestor-descendant relationship.
David S. Strait, Frederick E. Grine
Cladistic analysis was used to test the hypothesis that Australopithecus garhi is ancestral to the genus Homo. The data set of a prior cladistic analysis (Strait et al., 1997) was updated to account for recent fossil hominid discoveries, and reanalyzed. Current evidence suggests that A. garhi is the sister taxon of a clade that includes Homo, Paranthropus and A. africanus. Such a result is inconsistent with the hypothesis that A. garhi is the direct ancestor of the genus Homo. Conditions are specified under which future fossil finds might necessitate a revision of this conclusion.
Palabras clave / Keywords: australopithecus, Paranthropus, Homo, hominid phylogeny, cladistics, taxonomy.
The competing claims and requirements of classification (epistemological) and phylogeny (ontological) are briefly reviewed. Classification is a product of systematists, while phylogeny is a product of nature. For paleontologists the principal source of information about the evolutionary histories of groups of organisms is morphology, yet speciation and morphological shift are far from synonymous. This simple fact complicates everything from basic species recognition to phylogeny reconstructions involving higher taxa. It is concluded that in the interests of stability, simplicity, and effectiveness of communication, classifications should be consistent with what is known or can reasonably be inferred about phylogeny, but need not be exact transliterations of it. In the case of human beings and their close relatives it is clear that the evolutionary story has not been a simple linear process, but has instead involved extensive experimentation, with the production of numerous terminal species. These species must be accounted for in any classification that claims consistency with the fossil record.
Palabras clave / Keywords: classification, phylogeny, monophyly, diversity, species, evolution, hominidae.
Frederick S. Szalay
A variety of topics which play important roles in the systematics of fossil hominids are discussed. One of the major ontological/theoretical issues that influence the empirical work of species level taxonomy concerns the assumption that fossil hominid samples can be axiomatically considered terminal taxa. Another axiomatized practice is that of employing operational taxonomic units (OTUs) whereby nearly all samples of any level of distinction are considered valid species taxa. These unsubstantiated assumptions, coupled with punctuationist notions of species origin, intertwine to form a practice which results in a taxonomic distortion of what the probable evolutionary realities of evolving lineages were. The selection of extant taxonomic model species for delineating hominid species taxa has been a major issue of contention, and it will continue as long as observed ranges that include all known populations of any one single living hominoid model species continue to be ignored. Paleontological species taxa do not necessarily represent new lineages, but the iconography of taxograms (based on the practices noted) which routinely assume the latter to be phylogenetic trees imply a multitude of closed lineages. Such imagery is probably much more of an artifact than a tested reality of hominid evolutionary history. Examples are discussed.
Palabras clave / Keywords: taxonomic assumptions, phylogenetics, punctuationism, species taxa, lineages, paleoanthropology, stage vs. grade.
Classification of organisms must ultimately be grounded on similarities and differences of form and function. Gentic affinities are relevant and can be decisive in animal classification, but neither the magnitude nor the number of genetic mutations can constitute the essential criterion to resolve on taxonomic categories of animal organisms, since many diverse levels of organic construction mediate between genome composition and the adaptation and reproductive success of a population. Magnitude of time spans cannot be a criterion to define grades of hierarchy among taxonomic categories in organisms, since the tempo of diversification varies between two groups of organisms and within one stem or clade. The magnitude of morphofunctional innovations with vertical bipedality sufficies to decide at the taxonomic family level. Brain size and disproportions in the masticatory apparatus are decisive trends and combinations to distinguish Homo and Paranthropus as genera. Different conceptions in applying to fossil humans the species category are proposed to discussion.
Palabras clave / Keywords: classification, family, genus, Hominidae, Homo, Homo sapiens, hierarchy, organism, species, taxonomy
Systematics of Humankind. Statement from Palma 2000: An international Working Group on Systematics in Human Paleontology (Pág. 179-182)
Camilo J. Cela-Conde, Emiliano Aguirre
Systematics of Humankind. Statement from Palma 2000: An international Working Group on Systematics in Human Paleontology
Palabras clave / Keywords: humankind, paleontology, Homo
Rober E. Ulanowicz
Organicism, or the analogy by which various organized living communities are likened to individual discrete organisms, is rejected in many quarters by those who object to the notion of a larger entity forcing the behavior of its smaller constituents. The connections one may draw from organicism to vitalism and oppressive social regimes are all too obvious and unsavory. It is conceivable, however, that organic behavior may exist independently of the nearly deterministic confines of ontogeny. In ecosystems, for example, the configuration of processes among the community appears to influence the fates and behaviors of component populations in a non-deterministic fashion. Popper’s generalization of deterministic forces as “propensities,” when coupled with the notion of autocatalyic feedback, leads to a wholly natural and quantitative description of such organic behavior. There even exists a perspective from which the organic metaphor for living phenomena satisfies Occam’s criterion for simplicity better than the prevailing mechanistic metaphor for evolution. Judiciously reconstituted, organicism affords a highly useful and acceptable natural framework to help guide the scientific investigation of living systems.
Palabras clave / Keywords: autocatalysis, causality, contingency, development, ecosystem, evolution, feedback, neo-Darwinism, Newtonianism, Occam’s razor, organicism, organization, propensities, stochasticism.
This paper adresseses the search for an “ethics of survival”, an aspiration emerged from the increasing anxiety generated by the social and environmental degradation that threatens the future of mankind. Within this distressing situation, there is a reappearance in the field of ethical thinking of the spontaneous idea that an everlasting foundation for ethical precepts is required. With this intention in mind, the architects of universal ethics usually appeal to nature. Based on the arguments of David Hume, a critique is made of this equivoque that tries to derive ethical norms from the descriptive level, such tentative being based on a metaphysical-theological reflection, or on an empirical construction. As an alternative to this foundationist pretension, in the conclusion are presented pluralistic arguments for a pragmatical and theoretical development of ethical valuation.
Palabras clave / Keywords: ethics foundations, naturalistic fallacy, evolutionary ethics, autopoiesis, constructivism, intuition, naturalism.
Eduardo Césarman, Bruno Estañol
In order to describe themodynamics and bioenergetics, we thought it could be useful to offer some basic concepts of these disciplines in an almost aphoristic fashion.
Palabras clave / Keywords: themodynamics, bioenergetics
Cartesian tradition in medicine considers the body as a machine, and the physician as mechanic or at best an engineer, correcting the damaged sprockets, exchanging pieces and injecting a little oil or antibiotics here and there. This biomechanical model has served us well, but its limits are being felt, and just as Newtonian physics had to make way for newer theories, so will the venerable biomechanical model. The exceptions and failings are becoming impossible to ignore and we must explore alternatives. There is, however, a dilemma, for the alternatives hold not only serious consequences for medicine, but threaten to break down the very structure of scientific research in the biomedical fields
Palabras clave / Keywords: biomechanical, body, machine