Wednesday, September 25, 2013

New Approach to Explaining Evolution’s Big Bang

New Approach to Explaining Evolution’s Big Bang
Around 520 million years ago, many major groups of animals appear in the fossil record for the first time. Trilobites belonged to the same lineage as today's crustaceans and insects.
New York Times
September 19, 2013

The name Myllokunmingia may not ring a bell, but it is worth knowing. This 520-million-year-old creature was the size of a guppy, with a tiny swordfish-like fin running high over its back. The fossils it has left behind preserve traces of a skull.

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Humans have a skull, too. This and a number of other traits we share with Myllokunmingia reveal it to be one of the oldest, most primitive vertebrates yet found. It is, in other words, a hint of where we came from.

Myllokunmingia emerged during one of the most important phases in the history of life, an evolutionary boom known as the Cambrian explosion (named for the geological period when it took place). Over the course of about 20 million years, the oldest known fossils of most of the major groups of living animals appear, revealing a rapid diversification of life that led directly to humans.

“It’s rapid in geological terms, but it’s probably not rapid to anyone who’s not a geologist,” said Paul Smith, the director of the Oxford Museum of Natural History.

By some estimates, the first animals evolved about 750 million years ago. But it’s not until around 520 million years ago that many major groups of living animals left behind their first fossils. For decades, scientists have searched for the trigger that set in motion this riot of diversity in the animal kingdom.

Recently, Dr. Smith and his colleague David Harper of the University of Durham took a look at the hypotheses that have been offered about what caused the Cambrian explosion. “It became apparent just how many hypotheses there were out there,” Dr. Harper said. “Thirty-plus over the past 10 years.”

The scientists found that many of those explanations had boiled the cause down to just one trigger. Geologists suggested geological causes. Ecologists proposed ecological ones. Many of those ideas have merit, Dr. Smith and Dr. Harper argue in a commentary in this week’s Science, but it’s a mistake to search for a single cause. They propose that a tangled web of factors and feedbacks were responsible for evolution’s big bang.

Long before the Cambrian explosion, Dr. Smith and Dr. Harper argue, one lineage of animals had already evolved the genetic capacity for spectacular diversity. Known as the bilaterians, they probably looked at first like little crawling worms. They shared the Precambrian oceans with other animals, like sponges and jellyfish. During the Cambrian explosion, relatively modest changes to their genes gave rise to a spectacular range of bodies.

But those genes evolved in bilaterians tens of millions of years before the Cambrian explosion put them to the test, notes Dr. Smith. “They had the capacity,” he said, “but it hadn’t been expressed yet.”

It took a global flood to tap that capacity, Dr. Smith and Dr. Harper propose. They base their proposal on a study published last year by Shanan Peters of the University of Wisconsin and Robert Gaines of Pomona College. They offered evidence that the Cambrian Explosion was preceded by a rise in sea level that submerged vast swaths of land, eroding the drowned rocks.

“There’s a big kick that correlates with the sea level rise,” Dr. Smith said of the fossil record. He and Dr. Harper propose that this kick happened thanks to the new habitats created by the sea level rise. These shallow coastal habitats were bathed in sunlight and nourished with eroding nutrients like phosphates. Animals colonized these new fertile habitats, Dr. Smith and Dr. Harper argue, and evolved to take up new ecological niches.

But these great floods also poisoned the ocean. The erosion of the coastlines released calcium, which can be toxic to cells. In order to survive, animals had to evolve ways to rid themselves of the poison. One solution may have been to pack the calcium into crystals, which eventually evolved into shells, bones, and other hard tissues. Dr. Smith doesn’t think it’s a coincidence that several different lineages of bilaterians evolved hard tissues during the Cambrian explosion, and not sooner.

These shells and other hard tissues sped up animal evolution even more. Predators could grow hard claws and jaws for killing prey, and their prey could evolve hard shells and spines to defend themselves. Animals became locked in an evolutionary arms race.

This new ecological food web grew even more complex. Bigger predators evolved that could eat smaller predators. Meanwhile, some bilaterians burrowed into the sea floor for the first time, allowing oxygen-rich seawater to flow into the sediment. Those first burrowers profoundly transformed the world’s oceans, creating yet another habitat that other oxygen-breathing animals could also invade. “That drives the diversification onward,” said Dr. Smith.

Kevin Peterson, a biologist at Dartmouth, praised Dr. Smith and Dr. Harper for pointing to the right way to study the Cambrian explosion. “We are long past identifying single triggers for the event,” he said. Dr. Peters agreed that taking a holistic view of the Cambrian explosion would lead to a better understanding of it. “It’ll be a fun next decade,” he predicted.

But Philip Donoghue of the University of Bristol does not think the links Dr. Smith and Dr. Harper use in their hypothesis are tight enough yet. Questions still remain, for example, about how long vertebrates and other animals groups already existed before they left behind fossils like Myllokunmingia. If animals diversified earlier, then scientists will need to look at earlier causes.

“Timing,” said Dr. Donoghue, “is everything.”

Saturday, September 21, 2013

Syria: 'Bashar al-Assad ordered me to gas people - but I could not do it'

Syria: 'Bashar al-Assad ordered me to gas people - but I could not do it'
General Zaher al-Sakat tells Richard Spencer that he was ordered three times to use chemical weapons against his own people in Syria - but he could not go through with it.
Richard Spencer
21 Sep 2013

Few thought that the Syrian regime's promise to destroy its chemical weapons would be the end of the story. Brigadier-General Zaher al-Sakat, a former chemical weapons chief in President Bashar al-Assad's own army, certainly did not.

Gen Sakat says he was ordered three times to use chemical weapons against his own people, but could not go through with it and replaced chemical canisters with ones containing harmless bleach. He also insists that all such orders had to come from the top – President Assad himself – despite insistent denials by the regime that it has never used chemical weapons. Now he also claims to have his own intelligence that the Syrian president is evading the terms of a Russian-brokered deal to destroy his chemical weapons by transferring some of his stocks to his allies – Hizbollah, in Lebanon, and Iran. Gen Sakat spoke to The Sunday Telegraph last week, his first interview with a western newspaper, as Mr Assad confirmed for the first time what he and much of the rest of the world already knew – that regime possessed a huge arsenal of chemical weapons, and the delivery systems to go along with them. The Syrian leader's admission came in the form of written declarations on Friday and Saturday to the United Nations' Organisation for the Prohibition of Chemical Weapons. It was an extraordinary and unexpected outcome of the wrangling between the United States and Russia which followed the murderous attack on the Damascus suburbs of East and West Ghouta a month ago. But now attention is turning to whether Mr Assad will comply with the deal's terms – and whether it will lead to a wider opportunity to bring the warring parties together. On that score, both sides' backers, pleased with progress so far, profess less optimism. Gen Sakat's personal history gives new insight into the extent to which, it is said, the Assad regime gradually turned to the use of chemical weapons, despite angry public denials, after rebels encroached on Damascus and Aleppo, the country's two biggest cities, in the summer of last year. As chief scientific officer in the army's fifth division, he ran chemical weapons operations in the country's southern Deraa province, where the uprising began in March 2011. He says he witnessed the first uses of violence against peaceful protesters – and the first use of "dirty tricks", placing weapons in the mosque where the protests started to suggest the protesters were armed. Gen Sakat said the regime wanted to "annihilate" the opposition using any means, and said he received his first orders to use chemical weapons in October last year. On three occasions, he said he was told to use a mixture of phosgene and two other chlorine-based agents against civilian targets in Sheikh Masqeen, Herak, and Busra, all rebel-held districts. However, under cover of darkness, he said he had replaced the canisters containing the chemicals with ones containing water mixed with dilute bleach which would give off a similar chlorine smell. At first, his trick worked. "They were completely convinced that this was the same poisonous material," he told the Sunday Telegraph in an interview. "In this way I saved hundreds of lives of children and others." But after the third occasion, in January, his bosses became suspicious at the lack of deaths in his "attacks" and he began to plot his escape to Jordan, where he has been based since the spring. Gen Sakat believes chemical weapons have now been used 34 times, rather than the 14 occasions cited by international intelligence agencies. But he agrees with a variety of assessments that differing substances and concentrations are used, which would account for the differing death rates, with some attacks killing very few or none. Although phosgene has been banned internationally since the 1920s, it is much less potent than sarin, the chemical now known to have been deployed in Ghouta. The army was concerned not to use the most dangerous chemicals in the far south because of its proximity to Israel, Gen Sakat said. In other parts of the country, notably the Damascus suburbs, Homs and Aleppo, the regime was subsequently accused of using small quantities of stronger chemicals, culminating in the attack on Ghouta, where UN inspectors found traces of sarin across wide areas. The US, and the rebels themselves, believe that more than 1,400 people were killed there. Now the world waits to see whether Mr Assad will comply with the Russian-led deal to dismantle his nuclear stocks which saw American missile strikes postponed indefinitely. Last week, more details emerged of the behind-the-scenes negotiations which preceded the deal, and which make it seem like much less of a victory for Mr Assad. He will no doubt be aware of the subsequent fates of the two most recent Arab leaders to have abandoned their chemical weapons at the West's command – Saddam Hussein and Col Muammar Gaddafi. The proposal for Mr Assad to hand over his weapons had been discussed previously between the United States and Russia, so that the suggestion by John Kerry, the secretary of state, that it might be a way out of the missile crisis was less off-the-cuff than it appeared. Russia then enforced the deal on Mr Assad, despite Moscow's public claims that it was the rebels rather than the regime which perpetrated the Ghouta massacre. In another sign of Moscow's apparent scepticism, President Vladimir Putin said last week he was not "100 per cent sure" Mr Assad would comply, and the Kremlin's chief of staff, Sergei Ivanov, said on Saturday it was making contingency plans if he were to fail to do so. "I am speaking theoretically and hypothetically, but if we become convinced that Assad is cheating, we can change our position," he said. Gen Sakat says the deception has already begun. "Before the Lavrov deal, they were already mobilising them to move to Lebanon and even Iraq," he said. "There have already been weapons handed over to Hizbollah." Both the political opposition and the armed rebels have complained that the deal lets Mr Assad off the hook, making their claims that Mr Assad is now trying to hide his chemical weapons stocks convenient. Their claims cannot be verified, but they cite a variety of sources for their allegations. American newspapers have already reported western intelligence agencies' allegations that Unit 450, the central command-and-control structure of the chemical weapons programme, has been dispersing the arsenal to different sites inside the country. "We, along with many other international sources learned, through documents and other evidence about the transfer of Syrian chemical weapons to Hizbollah in Lebanon nearly three months ago," Fahad al-Masri, a spokesman for the western-backed Free Syrian Army said. He said the rebels had a network of informers inside the regime's chemical weapon apparatus, who sympathised with the rebels but were being prevented by threats to their lives from defecting. He said the FSA had also been shown intelligence estimates by western governments which said the same thing. He said the weapons were being stored at four sites under the direct control of Hizbollah. Gen Sakat says he has his own sources: a network inside the country of activists who are specifically monitoring the programme. One member, calling himself Abu Mohammed, told The Telegraph he had hacked into Unit 450 computer systems and read orders, including some relating to the transfer to Hizbollah. Gen Sakat said a team of his activists had observed a column of more than 20 vehicles, some identifiable as belonging to the programme, heading towards the Lebanese border. He also alleged that other stocks were being transferred through Iraq to Iran. "They saw these shipments start before Lavrov appeared and mentioned the deal," he said. International agencies are monitoring the possible transfer of weapons to Lebanon closely, and Israel has declared this its own "red line" – and it has already bombed Syria twice since the start of the uprising, including Unit 450's presumed base north of Damascus. Israeli intelligence sources would not comment on the allegations. But one retired Israeli Major-General and former attache to Washington, Gadi Shamni, said: "I am positive they're already trying to move things from one location to another to hide it. "It will be very hard to cheat in one week. But November is a very long time away – in winter, the sky is cloudy, and visibility is low. US satellites cannot be very effective – it's a very problematic issue and the Syrians understand it very well." Additional reporting by Inna Lazareva