Instead of one universal evolutionary tree, picture a three-trunk stand sharing a communal root system. A new theory of cellular evolution published in the current issue of the Proceedings of the National Academy of Sciences rejects Charles Darwin¿s Doctrine of Common Descent—the idea that all organisms are derived from a single primordial ancestor. Instead, Carl Woese of the University of Illinois-Champaign proposes that the three cell types that comprise life on earth arose from three forms of proto cells that swam together in a dense genetic soup, freely sharing their DNA.
Indeed, such DNA swapping was the driving force in the evolution of unicellular organisms, Woese argues. Biologists have traditionally credited this so-called horizontal gene transfer with just a minor role in cellular evolution. But Woese asserts that only by sharing their genes—or evolutionary inventions, as he calls them—could simple cellular organizations have given rise to more complex cell designs. In the beginning, he says, primitive cells "did not have stable genealogical records." But eventually, these lines—including the three that spawned all extant life forms—reached what Woese terms the "Darwinian threshold," the point at which a lineage matures to genetic stability. Here the cellular organization became fixed, leading to a traceable cell line via reproduction. "Crossing a Darwinian threshold leads to a more solidified, organized cellular design," he explains.
The idea could overturn conventional cell evolution wisdom. Instead of the individual, "it is the community as a whole, the ecosystem which evolves," Woese remarks. "We can¿t expect to explain cellular evolution if we stay locked in the classical Darwinian mode of thinking," he adds. "The time has come for biology to go beyond the Doctrine of Common Descent."
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2 Comments
Add CommentPlease elaborate on the three primordial cell types, and why they are distinct and unable to share genetic material.
Reply | Report Abuse | Link to thisThis summary is unclear and seemingly self-contradictory.
Reply | Report Abuse | Link to thisThe theory it summarizes supposedly: "proposes that the three cell types that comprise life on earth arose from three forms of proto cells that swam together in a dense genetic soup, freely sharing their DNA."
It is (1) unclear from this whether the theory proposes three independent events in which protocells evolved and then subsequently shared their DNA.
But even if that is the case, it is (2) contradictory to talk about independent origins of three cell types that then subsequently "freely shared" their DNA.
If they are "freely sharing" their DNA, how do they remain distinct cell types?
If they are "freely sharing" their DNA, they would become in effect the one common ancestor.
Perhaps what the new theory really states is that they partially shared their DNA.