IN JUST a few weeks single-celled yeast have evolved into a multicellular organism, complete with division of labour between cells. This suggests that the evolutionary leap to multicellularity may be a surprisingly small hurdle.
Multicellularity has evolved at least 20 times since life began, but the last time was about 200 million years ago, leaving few clues to the precise sequence of events. To understand the process better, William Ratcliff and colleagues at the University of Minnesota in St Paul set out to evolve multicellularity in a common unicellular lab organism, brewer's yeast.
Their approach was simple: they grew the yeast in a liquid and once each day gently centrifuged each culture, inoculating the next batch with the yeast that settled out on the bottom of each tube. Just as large sand particles settle faster than tiny silt, groups of cells settle faster than single ones, so the team effectively selected for yeast that clumped together.
Sure enough, within 60 days - about 350 generations - every one of their 10 culture lines had evolved a clumped, "snowflake" form. Crucially, the snowflakes formed not from unrelated cells banding together but from cells that remained connected to one another after division, so that all the cells in a snowflake were genetically identical relatives. This relatedness provides the conditions necessary for individual cells to cooperate for the good of the whole snowflake.
"The key step in the evolution of multicellularity is a shift in the level of selection from unicells to groups. Once that occurs, you can consider the clumps to be primitive multicellular organisms," says Ratcliff.
In some ways, the snowflakes do behave as if they are multicellular. They grow bigger by cell division and when the snowflakes reach a certain size a portion breaks off to form a daughter cell. This "life cycle" is much like the juvenile and adult stages of many multicellular organisms.
After a few hundred further generations of selection, the snowflakes also began to show a rudimentary division of labour. As the snowflakes reach their "adult" size, some cells undergo programmed cell death, providing weak points where daughters can break off. This lets the snowflakes make more offspring while leaving the parent large enough to sink quickly to the base of the tube, ensuring its survival. Snowflake lineages exposed to different evolutionary pressures evolved different levels of cell death. Since it is rarely to the advantage of an individual cell to die, this is a clear case of cooperation for the good of the larger organism. This is a key sign that the snowflakes are evolving as a unit, Ratcliff reported last week at a meeting of the Society for the Study of Evolution in Norman, Oklahoma.
Other researchers familiar with the work were generally enthusiastic. "It really seemed to me to have the elements of the unfolding in real time of a major transition," says Ben Kerr, an evolutionary biologist at the University of Washington in Seattle. "The fact that it happened so quickly was really exciting."
Sceptics, however, point out that many yeast strains naturally form colonies, and that their ancestors were multicellular tens or hundreds of millions of years ago. As a result, they may have retained some evolved mechanisms for cell adhesion and programmed cell death, effectively stacking the deck in favour of Ratcliff's experiment.
"I bet that yeast, having once been multicellular, never lost it completely," says Neil Blackstone, an evolutionary biologist at Northern Illinois University in DeKalb. "I don't think if you took something that had never been multicellular you would get it so quickly."
Even so, much of evolution proceeds by co-opting existing traits for new uses - and that's exactly what Ratcliff's yeast do. "I wouldn't expect these things to all pop up de novo, but for the cell to have many of the elements already present for other reasons," says Kerr.
Ratcliff and his colleagues are planning to address that objection head-on, by doing similar experiments with Chlamydomonas, a single-celled alga that has no multicellular ancestors. They are also continuing their yeast experiments to see whether further division of labour will evolve within the snowflakes. Both approaches offer an unprecedented opportunity to bring experimental rigour to the study of one of the most important leaps in our distant evolutionary past.
Parley P. Pratt wrote:We must lie to support brother Joseph, it is our duty to do so.
I simply do not understand complex evolutionary processes having anything to do with the existence or non-existence of God. It is as if someone said to me "God doesn't exist", I ask why and he responds, "because science has developed a complex theory called gravity".
my regards, mikwut
All communication relies, to a noticeable extent on evoking knowledge that we cannot tell, all our knowledge of mental processes, like feelings or conscious intellectual activities, is based on a knowledge which we cannot tell. -Michael Polanyi
"Why are you afraid, have you still no faith?" Mark 4:40
mikwut wrote:I simply do not understand complex evolutionary processes having anything to do with the existence or non-existence of God. It is as if someone said to me "God doesn't exist", I ask why and he responds, "because science has developed a complex theory called gravity".
my regards, mikwut
God's mouthpieces have long claimed that God was the agent behind the creation of and the diversity of life. That simply isn't true.
Parley P. Pratt wrote:We must lie to support brother Joseph, it is our duty to do so.
God's mouthpieces have long claimed that God was the agent behind the creation of and the diversity of life. That simply isn't true.
And evolution or your posted article shows he was not "the agent behind the creation of and the diversity of life" how? To make that simply true.
my regards, mikwut
All communication relies, to a noticeable extent on evoking knowledge that we cannot tell, all our knowledge of mental processes, like feelings or conscious intellectual activities, is based on a knowledge which we cannot tell. -Michael Polanyi
"Why are you afraid, have you still no faith?" Mark 4:40
I equate the sophistication of the spaghetti monster with creationists depictions of dinasours living with people 5000 years ago, both are children playing with toys. Your confusing conceptions of God with the existence of God - conceptions can be refined and wrong without eliminating the original hypothesis.
Second, your confusing efficient causes with final causes.
Third, I missed the parts in the article about the beginning of the universe, the laws of the universe, the sustaining of the universe, information, consciousness, abiogenesis and how they came about even in an efficiently caused manner. Your answers leave me where I began I simply do not understand why a scientific descriptive theory of the processes of biological development would have any falsification of a transcendent being. Your answers leave me just as intellectually unsatisfied.
It is quite possible that some of your prior conceptions of a God being and the role he played in creation have been eliminated by your understanding of evolution.
my regards, mikwut
All communication relies, to a noticeable extent on evoking knowledge that we cannot tell, all our knowledge of mental processes, like feelings or conscious intellectual activities, is based on a knowledge which we cannot tell. -Michael Polanyi
"Why are you afraid, have you still no faith?" Mark 4:40
I equate the sophistication of the spaghetti monster with creationists depictions of dinasours living with people 5000 years ago, both are children playing with toys. Your confusing conceptions of God with the existence of God - conceptions can be refined and wrong without eliminating the original hypothesis.
Second, your confusing efficient causes with final causes.
Third, I missed the parts in the article about the beginning of the universe, the laws of the universe, the sustaining of the universe, information, consciousness, abiogenesis and how they came about even in an efficiently caused manner. Your answers leave me where I began I simply do not understand why a scientific descriptive theory of the processes of biological development would have any falsification of a transcendent being. Your answers leave me just as intellectually unsatisfied.
It is quite possible that some of your prior conceptions of a God being and the role he played in creation have been eliminated by your understanding of evolution.
my regards, mikwut
I'm not saying every transcendent being has been falsified - just the God of the Bible, and any other gods claiming to have created life on earth. This alone discredits the beloved El/Yahweh syndicate. After all, the only thing we know about this syndicate is what is published about it in holy writ.
The FSM was a little joke. Very little, it's true.
Parley P. Pratt wrote:We must lie to support brother Joseph, it is our duty to do so.
It doesn't discredit the God of the Bible, again a phrase wrought with differing conceptions. There is nothing unreasonable about understanding the God of the Bible creating through the operation of created principles, evolution being some of them, which we partially understand in scientific laws.
Your conceptual problem follows you into evolution as well. Evolution occurred for sure but the naturalistic and metaphysical consequences of that are still reasonably debated and not fully understood. For example, I am fascinated by Simon Conway Morris' idea of convergence. He provides a compelling case for convergence in, "Life's Solution: Inevitable Humans in a Lonely Universe". This isn't ID or creationism, it is decrying them as well as their equivalent fundamentalists like Dawkins. The idea is opposite Stephen Jay Gould's idea that evolution would show a different movie if you rewound the tape. Morris argues we are inevitable, that implies purposeful and your article doesn't disprove that, it is actually perfectly consistent with the idea. Of course I don't accept that as proof in a way analogous to how you utilize evolution against God but as an illustration of how feeble it is to say unicellular organisms combining and evolving through complex ways disprove a creator God, or the God or the Bible.
my regards, mikwut
All communication relies, to a noticeable extent on evoking knowledge that we cannot tell, all our knowledge of mental processes, like feelings or conscious intellectual activities, is based on a knowledge which we cannot tell. -Michael Polanyi
"Why are you afraid, have you still no faith?" Mark 4:40
