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Jeffrey H Schwartz

Publications and source records attributed to Jeffrey H Schwartz.

9 recordsLinked to original sources
PubMed2006

Sudden origins: a general mechanism of evolution based on stress protein concentration and rapid environmental change.

A major theme in Darwinian evolutionary theory is that novelty arises through a process in which organisms and their features are gradually transformed. Morgan provided Darwinism and the evolutionary synthesis with the idea that minor mutations produce the minuscule morphological variations on which natural selection then acts, and that, although mutation is random, once a process of gradual genetic modification begins, it becomes directional and leads to morphological, and consequently organismal, transformation. In contrast, studies on the role of cell membrane physical states in regulating the expression of stress proteins in response to environmental shifts indicate the existence of a downstream mechanism that prevents or corrects genetic change (i.e., maintains "DNA homeostasis"). However, episodic spikes in various kinds of environmental stress that exceed an organism's cells' thresholds for expression of proper amounts of stress proteins responsible for protein folding (including stochastically occurring DNA repair) may increase mutation rate and genetic change, which in turn will alter the pattern of gene expression during development. If severe stress disrupts DNA homeostasis during meiosis (gametogenesis), this could allow for the appearance of significant mutational events that would otherwise be corrected or suppressed. In evolutionary terms, extreme spikes in environmental stress make possible the emergence of new genetic and consequent developmental and epigenetic networks, and thus also the emergence of potentially new morphological traits, without invoking geographic or other isolating mechanisms.

Animals↗
PubMed2006

Race and the odd history of human paleontology.

Although the late 17th century witnessed the recognition of fossils as the remains of extinct organisms-because they could be incorporated into the creation story embodied in the Great Chain of Being-acceptance of human antiquity through the indisputable demonstration of the contemporaneity of human bones, stone tools, and accepted fossils was not forthcoming for nearly 2 centuries thereafter. When it did occur, however, ancient humans were not seen as presenting a pattern of diversity similar to that seen in the fossil records of nonhuman organisms. Instead, human evolution then, as now, has typically been interpreted as being unilinear. This belief can be traced to Huxley (1863), who argued that the Feldhofer Grotto Neanderthal skullcap was merely an extension into the past of morphology seen in the Australian Aborigine, whom he took to represent the primitive end of an extreme range of variation he thought characterized Homo sapiens. During the mid-20th century, Mayr and Dobzhansky (mis)used their clout as founders of the evolutionary synthesis to cement in paleoanthropology the idea that human evolutionary history was characterized by nonspeciation. As such, anything that could be interpreted as potentially representing taxic diversity was relegated to the status of individual variation. Lack of understanding of the history of human paleontology, and the biases that constrained its perspective on human evolution, continue to affect the ways in which most paleoanthropologists pigeonhole human fossils.

Animals↗
PubMed2005

Human foot bones from Klasies River main site, South Africa.

The caves at Klasies River contain abundant archaeological evidence relating to human evolution in the late Pleistocene of southern Africa. Along with Middle Stone Age artifacts, animal bones, and other food waste, there are hominin cranial fragments, mandibles with teeth, and a few postcranial remains. Three foot bones can now be added to this inventory. An adult first metatarsal is similar in size and discrete anatomical features to those from Holocene burials in the Cape Province. A complete and well-preserved second metatarsal is especially long and heavy at midshaft in comparison to all Holocene and more recent South African homologues. A large fifth metatarsal is highly distinctive in its morphology. In overall size, these pedal elements resemble specimens from late Pleistocene sites in western Asia, but there are some differences in proportions. The fossils support earlier suggestions concerning a relatively high level of sexual dimorphism in the African Middle Stone Age population. Squatting facets on the two lateral metatarsals appear to indicate a high frequency of kneeling among members of this group. The new postcranial material also underlines the fact that the morphology of particular skeletal elements of some of the 100,000-year-old Klasies River individuals falls outside the range of modern variation.

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PubMed2004

Barking up the wrong ape--australopiths and the quest for chimpanzee characters in hominid fossils.

With the shift during the 1980s from a human-great ape ultimately to an orangutan-(gorilla-(human-chimp)) theory of relatedness, the search for chimpanzee-like features in early hominids intensified. Reconstructions of early hominids became caricatures of chimpanzees, not only in soft tissue features (e.g. the nasal region), but in supposed bony structures (e.g. an anteriorly and especially superiorly protruding a supraorbital torus with a distinct posttoral sulcus behind). In spite of rampant >>Panophilia,<< actual morphologies of the majority of early hominid specimens are those cited as uniting an orangutan clade. Those specimens that are >>chimpanzee-like<< are probably not cladistically hominid.

Africa↗
PubMed2002

Is paleoanthropology science? Naming new fossils and control of access to them.

Progress in paleoanthropology is impeded when new fossil materials are published but unavailable for comparative study, as is too often the case. In this commentary, we review the stages of description and analysis that new fossils must undergo and conclude that it is disingenuous to argue that fossils have not been properly "published" when descriptions and new names formulated in accordance with the International Code of Zoological Nomenclature have appeared in leading scientific journals. Once such names and descriptions have been published, it is imperative that the original fossils concerned be available to the scientific community for comparative analysis, for by the very nature of science, no statement about such fossils, however carefully prepared by the original describers (or anyone else), can be regarded as definitive. Science is a system of provisional knowledge that constantly requires re-examination and testing. It cannot function as a system in which assertions have to be left unchallenged for want of free access to the primary data.

Animals↗