Abiogenesis & Evolution


EVOLUTION: ON THE EVOLUTION OF HUMANS AND CHIMPANZEES: "What does the chimpanzee genome sequence tell us about the role of natural selection in human evolution? Purifying selection is clearly evidenced by the fact that mutations that alter the amino acid sequence, which in many cases presumably have a deleterious effect, have gone to fixation at a much lower rate than those that do not. Traditionally, this is expressed in terms of the ratio of non-synonymous (dN) to synonymous (dS) substitutions, dN/dS, where dS is here used as an index of the rate of unconstrained, neutral evolution. When dN/dS is less than 1, the usual interpretation is that negative selection has taken place on non-synonymous substitutions. When dN/dS is greater than 1, positive selection is likely to have accelerated the rate of fixation of non-synonymous substitutions. Note that purifying selection is the conservative force in molecular evolution, whereas positive selection is the diversifying force that drives molecular adaptation. dN/dS is estimated to be ~0.25, on average, for the human chimp comparison. In other words, about 75% of all amino acid replacements seem to be removed by purifying selection."

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How many Biological Species of Hominids

The Woodstock of Evolution -- The World Summit on Evolution (ScientificAmerican.com): U.C. Berkeley paleoanthropologist Timothy White said, 'A glance at the extant fossil record looks like Gould was right. There are at least two dozen fossil species in six million years of hominid evolution. However, says White, the bush is not so bushy. 'Name diversity does not equal biological diversity.' The problem lies in the difference between 'lumpers' and 'splitters' in species classification. The academic pressures to publish extraordinary new discoveries dictates that if you want to get your fossil find published in Science or Nature, and you want the cover illustration, you cannot conclude that your fossil is yet another Australopithicus africanus, for example. For such purposes, it's better come up with an interpretation indicating that this new find you are revealing for the first time to the world is the most spectacular discovery of the last century and that it promises to overturn hominid phylogeny and send everyone back to the drawing board to reconfigure the human evolutionary tree. Training a more skeptical eye on many of these fossils, however, shows that many, if not most of these fossils belong in already well-established categories. White concludes that the specimen labeled Kenyanthropus platyops, for example, is very fragmented and is most likely just another Australopithicus africanus.

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Redating Of The Latest Neandertals In Europe

Redating Of The Latest Neandertals In Europe: "An international team of researchers has redated the two Neandertals from Vindija Cave, the results of which have been published in the Jan. 2-6 early edition of the journal Proceedings of the National Academy of Sciences (PNAS).

The resultant ages are between 32,000 and 33,000 years ago, and perhaps slightly older. In 1998, the fossils had been radiocarbon dated to 28,000-29,000 years ago.
Since that time, the increasing application of direct radiocarbon dating to late Neandertal and early modern human fossils in Europe has greatly altered perceptions of the chronological relationships between Neandertals and modern humans during the time that the latter spread westward across Europe.

In particular, it has shown that many of the purportedly early modern human fossils are much more recent, while confirming the early ages of important fossil samples in central and eastern Europe. This work has been combined recently with refinements in the sample purification techniques for the radiocarbon dating bone and teeth, to provide more accurate, and usually older, dates for important fossil specimens.

These new fossil ages still document a substantial chronological overlap between Neandertals and modern humans in Europe, but primarily the work highlights the currently tenuous nature of scenarios of modern human dispersals in Europe based on small numbers of direct radiocarbon dates, using various sample preparation protocols, on diagnostic human fossils in this time range."

The original news release can be found here.

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Homo floresensis

Science & Technology at Scientific American.com: The Woodstock of Evolution -- The World Summit on Evolution, held in the Galapagos Islands, revealed a science rich in history and tradition, data and theory, as well as controversy and debate: "Found in Liang Bua cave, the type specimen of Homo floresiensis was dated at 18,000 years old, meaning that they had to be modern humans because all other hominid species had long ago gone extinct. But with a cranial capacity of only 300 cubic centimeters--about the same size as that of Lucy and modern chimpanzees--this means that they were able to fashion complex tools (and possibly boats) with tiny brains; the implication is that brain architecture, not size, is what counts for creating higher intelligence. A second published specimen put to rest the pathology hypothesis that Homo floresensis was a microcephalic human. The best evidence, says White, points to insular dwarfing, a rapid punctuation event out of Homo sapiens that led to a shrinkage of these isolated people. Such dwarfing effects can be seen on this and other islands, where large mammals get smaller (like the dwarf elephant), and small reptiles get larger (like the Komodo Dragon). The chances of any living members of this species still existing in the hinterlands of Flores are extremely remote, but some observers have noted that the indigenous peoples of Flores recount a myth of small hairy humans who descend from the highlands to steal food and supplies."

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Evolutionary Explanations For Aging Plateau

The End Of Aging? New Study Examines Evolutionary Explanations For 'Biological Immortality': "'For decades, demographers and gerontologists noticed that late life human data did not fit [expected] models: there was a shortage of deaths,' write Michael R. Rose, Casandra L. Rauser, and Laurence D. Mueller. 'More specifically, the exponential increase in age-specific death rate seemed to slow down considerably, if not cease.'

The sudden plateau in mortality rates after a certain age has long been observed with other organisms, but its presence in human populations has been dismissed as a result of the advent of nursing homes and modern medicine. However, close examination of demographic data supports a distinct third phase of life history known as "late life," characterized by the cessation of age-related deterioration.

"Late life is a unique and distinct phase of life very different from aging," write the authors. "Each phase evolves according to very different rules. Evolutionary biology has a new set of problems to solve."

The authors posit that late life arises after the forces of natural selection affecting both fertility and mortality cease to have an impact."

Rose, Michael R., Casandra L. Rauser, Laurence D. Mueller. "Late Life: A New Frontier for Physiology." Physiological and Biochemical Zoology 78:6.

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