Saturday, February 26, 2011

Oldest fossils of large seaweeds, possible animals tell story about oxygen in an ancient ocean

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Almost 600 million years ago, before the rampant evolution of diverse life forms known as the Cambrian explosion, a community of seaweeds and worm-like animals lived in a quiet deep-water niche under the sea near what is now Lantian, a small village in Anhui Province of South China. Then they simply died, leaving some 3,000 nearly pristine fossils preserved between beds of black shale deposited in oxygen-free waters.

Scientists from the Chinese Academy of Sciences, Virginia Tech in the U.S., and Northwest University in Xi'an, China report the discovery of the fossils and the mystery in the Feb. 17 issue of Nature.

In addition to perhaps ancient versions of algae and worms, the Lantian biota – named for its location – included macrofossils with complex and puzzling structures. In all, scientists identified about 15 different species at the site.

The fossils suggest that morphological diversification of macroscopic eukaryotes – the earliest versions of organisms with complex cell structures -- may have occurred only tens of millions of years after the snowball earth event that ended 635 million years ago, just before the Ediacaran Period. And their presence in the highly organic-rich black shale suggests that, despite the overall oxygen-free conditions, brief oxygenation of the oceans did come and go.

"So there are two questions," said Shuhai Xiao, professor of geobiology in the College of Science at Virginia Tech. "Why did this community evolve when and where it did? It is clearly different in terms of the number of species compared to biotas preserved in older rocks. There are more species here and they are more complex and larger than what evolved before. These rocks were formed shortly after the largest ice age ever, when much of the global ocean was frozen. By 635 million years ago, the snowball earth event ended and oceans were clear of ice. Perhaps that prepared the ground for the evolution of complex eukaryotes."

The team was examining the black shale rocks because, although they were laid down in waters that were not good for oxygen-dependent organisms, "they are known to be able to preserve fossils very well," said Shuhai. "In most cases, dead organisms were washed in and preserved in black shales. In this case, we discovered fossils that were preserved in pristine condition where they had lived – some seaweeds still rooted."

The conclusion that the environment would have been poisonous is derived from geochemical data, "but the bedding surfaces where these fossils were found represent moments of geological time during which free oxygen was available and conditions were favorable. They are very brief moments to a geologist," said Xiao. "but long enough for the oxygen-demanding organisms to colonize the Lantian basin and capture the rare opportunities."

The research team suggests in the article in Nature that the Lantian basin was largely without oxygen but was punctuated by brief oxic episodes that were opportunistically populated by complex new life forms, which were subsequently killed and preserved when the oxygen disappeared. "Such brief oxic intervals demand high-resolution sampling for geochemical analysis to capture the dynamic and complex nature of oxygen history in the Ediacaran Period," said lead author Xunlai Yuan, professor of palaeontology with the Chinese Academy of Sciences.

Proving that hypothesis awaits further study. The rocks in the study region are deposited in layered beds. The nature of the rock changes subtly and there are finer and finer layers that can be recognized within each bed. "We will need to sample each layer to see whether there is any difference in oxygen contents between layers with fossils and those without" said co-author Chuanming Zhou, professor of palaeontology with the Chinese Academy of Sciences.

(Photo: Zhe Chen)


Zinc reduces the burden of the common cold

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Zinc supplements reduce the severity and duration of illness caused by the common cold, according to a systematic review published in The Cochrane Library. The findings could help reduce the amount of time lost from work and school due to colds.

The common cold places a heavy burden on society, accounting for approximately 40% of time taken off work and millions of days of school missed by children each year. The idea that zinc might be effective against the common cold came from a study carried out in 1984, which showed that zinc lozenges could reduce how long symptoms lasted. Since then, trials have produced conflicting results and although several biological explanations for the effect have been proposed, none have been confirmed.

The review updates a previous Cochrane Systematic Review, carried out in 1999, with data from several new trials. In total, data from 15 trials, involving 1,360 people, were included. According to the results, zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms reduce the severity and length of illness. At seven days, more of the patients who took zinc had cleared their symptoms compared to those who took placebos. Children who took zinc syrup or lozenges for five months or longer caught fewer colds and took less time off school. Zinc also reduced antibiotic use in children, which is important because overuse has implications for antibiotic resistance.

"This review strengthens the evidence for zinc as a treatment for the common cold," said lead researcher Meenu Singh of the Post Graduate Institute of Medical Education and Research in Chandigarh, India. "However, at the moment, it is still difficult to make a general recommendation, because we do not know very much about the optimum dose, formulation or length of treatment."

Further research should focus on the benefits of zinc in defined populations, the review suggests. "Our review only looked at zinc supplementation in healthy people," said Singh. "But it would be interesting to find out whether zinc supplementation could help asthmatics, whose asthma symptoms tend to get worse when they catch a cold." The researchers also say that more work needs to be carried out in low-income countries, where zinc deficiency may be prevalent.

Wiley

Earliest humans not so different from us, research suggests

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That human evolution follows a progressive trajectory is one of the most deeply-entrenched assumptions about our species. This assumption is often expressed in popular media by showing cavemen speaking in grunts and monosyllables (the GEICO Cavemen being a notable exception). But is this assumption correct? Were the earliest humans significantly different from us?

In a paper published in the latest issue of Current Anthropology, archaeologist John Shea (Stony Brook University) shows they were not.

The problem, Shea argues, is that archaeologists have been focusing on the wrong measurement of early human behavior. Archaeologists have been searching for evidence of "behavioral modernity", a quality supposedly unique to Homo sapiens, when they ought to have been investigating "behavioral variability," a quantitative dimension to the behavior of all living things.

Human origins research began in Europe, and the European Upper Paleolithic archaeological record has long been the standard against which the behavior of earlier and non-European humans is compared. During the Upper Paleolithic (45,000-12,000 years ago), Homo sapiens fossils first appear in Europe together with complex stone tool technology, carved bone tools, complex projectile weapons, advanced techniques for using fire, cave art, beads and other personal adornments. Similar behaviors are either universal or very nearly so among recent humans, and thus, archaeologists cite evidence for these behaviors as proof of human behavioral modernity.

Yet, the oldest Homo sapiens fossils occur between 100,000-200,000 years ago in Africa and southern Asia and in contexts lacking clear and consistent evidence for such behavioral modernity. For decades anthropologists contrasted these earlier "archaic" African and Asian humans with their "behaviorally-modern" Upper Paleolithic counterparts, explaining the differences between them in terms of a single "Human Revolution" that fundamentally changed human biology and behavior. Archaeologists disagree about the causes, timing, pace, and characteristics of this revolution, but there is a consensus that the behavior of the earliest Homo sapiens was significantly that that of more-recent "modern" humans.

Shea tested the hypothesis that there were differences in behavioral variability between earlier and later Homo sapiens using stone tool evidence dating to between 250,000- 6000 years ago in eastern Africa. This region features the longest continuous archaeological record of Homo sapiens behavior. A systematic comparison of variability in stone tool making strategies over the last quarter-million years shows no single behavioral revolution in our species' evolutionary history. Instead, the evidence shows wide variability in Homo sapiens toolmaking strategies from the earliest times onwards. Particular changes in stone tool technology can be explained in terms of the varying costs and benefits of different toolmaking strategies, such as greater needs for cutting edge or more efficiently-transportable and functionally-versatile tools. One does not need to invoke a "human revolution" to account for these changes, they are explicable in terms of well-understood principles of behavioral ecology.

This study has important implications for archaeological research on human origins. Shea argues that comparing the behavior of our most ancient ancestors to Upper Paleolithic Europeans holistically and ranking them in terms of their "behavioral modernity" is a waste of time. There are no such things as modern humans, Shea argues, just Homo sapiens populations with a wide range of behavioral variability. Whether this range is significantly different from that of earlier and other hominin species remains to be discovered. However, the best way to advance our understanding of human behavior is by researching the sources of behavioral variability in particular adaptive strategies.

The University of Chicago Press

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