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5 December 2013 11:26 am ,
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An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Early Life Gets More Complicated
21 June 2002 (All day)
A new theory suggests that in the earliest years of life on Earth, dozens of types of loosely organized protocells engaged in an active swap meet as they exchanged and tested what are now the basic building blocks of the cell. The scenario differs somewhat from the classic tenet, proposed by Charles Darwin, that all of today's life evolved from a single ancestral form.
Biologists have struggled for years to explain how modern cells arose. The three basic groups--bacteria, single-celled microbes called archaea, and eukarya such as plants and us--each contain machinery that deciphers genetic blueprints and produces critical proteins. But the cells' machinery varies fundamentally across the three basic groups of life. Evolutionist Carl Woese of the University of Illinois, Urbana-Champaign, who proposed the now-accepted classification of the three branches of life (Science, 2 May 1997, p. 699), says it has been unclear how such distinct cell types could have evolved from a single ancestral cell.
To come up with an explanation, Woese spent several years comparing genes from many of the 63 microbes whose genomes have been sequenced since the mid-1990s. He focused on cellular components that were likely to be around during early evolution: the building blocks of the cell's ribosomes, which assemble proteins, and the enzymes that ferry amino acids to the ribosome. Billions of years ago, gene transfer between microbe species was much more common than it is today, Woese claims the data show. He speculates that in the distant past, a variety of basic cell types freely exchanged genes and components, such as DNA-replication enzymes. As cell components became more interdependent, the organisms became unable to try out new designs. After that critical point, which Woese calls the "Darwinian threshold," the organisms began to evolve largely independently of one another.
"I think it's a really coherent and poetic vision," says molecular biologist W. Ford Doolittle of Dalhousie University in Halifax, Nova Scotia, who claims that other evolutionary biologists continue to accept a simpler vision, that a single common ancestral cell led to all modern life. But the data don't exclude other scenarios, he says, including one in which species readily exchanged genes after clear lineages formed.