Posted on 01/17/2012 6:18:07 AM PST by LibWhacker
By watching evolution in progress, scientists reveal key developments in the evolution of complex life and put evolutionary theories to the test
The transition from single-celled to multicellular organisms was one of the most significant developments in the history of life on Earth. Without it, all living things would still be microscopic and simple; there would be no such thing as a plant or a brain or a human. How exactly multicellularity arose is still a mystery, but a new study, published January 16 in Proceedings of the National Academy of Sciences, found that it may have been quicker and easier than many scientists expected.
"This is a significant paper that addresses one of the most fundamental questions in evolutionary and developmental biology," says Rick Grosberg, an evolutionary biologist at the University of California at Davis, who was not involved with the research.
Since evolution acts on individual cells, it pays off for a cell to be selfish. By hogging resources and hindering neighbors, a cell can increase the odds that more of its own genes get passed into the next generation. This logic is one of the reasons it has been challenging to imagine how multicellularity arose; it requires the subjugation of self-interest in favor of the group’s survival.
"Traditional theories make this out to be a difficult transition because you have to somehow turn off selection on the individual cells and turn it on for the collective," says Carl Simpson, a paleobiologist at the Museum für Naturkunde in Berlin, Germany, who also was not involved in the research. "The big result here is that these transitions can be super easy."
In the new paper, researchers at the University of Minnesota at Minneapolis used a simple but elegant technique to artificially select for multicellularity in yeast. They dumped unicellular yeast into a tube of liquid food and waited a few minutes for the cells to settle. Then they extracted the lowest fraction of the liquid and allowed whatever cells it contained to form the next generation. Because the cells had to cluster together in order to sink to the bottom and survive, the artificial selection made it more advantageous for yeast to cooperate than to be solitary.
After just 60 generations, all of the surviving yeast populations had formed snowflake-shaped multicellular clusters. "Hence we know that simple conditions are sufficient to select for multicellularity," says biologist Michael Travisano, who led the research.
But at what point do the yeast become something more than a cluster of cells? When do they begin behaving as one organism?
In a true multicellular organism, such as a rabbit, evolution acts upon the rabbit and not upon each of the billions of cells that build it. So the researchers set out to determine whether artificial selection would act upon the snowflake yeast as if they too were multicellular organisms. To test it, one batch of the multicellular yeast was allowed only five minutes to settle in a tube (representing a strong selection pressure), while another batch was given 25 minutes (a weaker selection pressure). After 35 generations, the yeast that were exposed to stronger selection evolved to have larger cluster sizes, while those in the weak selection group actually shrank in size. This indicated that each cluster of cells was evolving as one organism.
In addition, time-lapse photography [video below] revealed that, in order to reproduce, the multicellular yeast divides itself into branches that develop into the multicellular form as well. The daughter clusters did not create their own offspring until they had reached a similar size as their parents. The presence of this juvenile stage shows that the snowflake yeast had adopted a multicellular way of life, says William Ratcliff, a postdoctoral student in Travisano’s lab.
The researchers also found evidence of rudimentary division of labor, which is an essential characteristic for more complex multicellular life forms. In a human, for example, some cells may differentiate into blood cells, others may differentiate into immune cells, but only select egg or sperm cells help form the next generation.
In the multicellular yeast, the division of labor was more subtle. Although the experiment's artificial selection favored large clusters, a large cluster required more time to grow before it could reproduce. That meant that smaller clusters, which divide in half more quickly, could soon outnumber the larger clusters. But after many generations of selection, the large clusters evolved a solution: non-reproductive cells which served as points where offspring could break away from the parent cluster. By providing more break points, these specialized cells allowed the clusters to break into more pieces, to produce a greater number offspring quickly.
“The discovery that there are cells specialized to die in order for the structure to reproduce is suggestive of the first steps toward cellular differentiation,” Grosberg says.
Although researchers agree that the yeast clusters could indeed be considered multicellular organisms, they remain relatively simple. "The researchers are not going to evolve sponges with this approach, but it's amazing what they’re able to do so quickly," Simpson says.
The fast evolution was not all that surprising to Grosberg, who has written papers arguing that multicellularity should be relatively easy to evolve; other researchers have estimated that multicellularity has arisen independently on at least 25 different occasions throughout the history of life. Yet nobody really knew how it originated, or what steps were involved in the process. By watching evolution in progress, the new research uncovered experimental evidence for these theories and revealed one possible scenario of how multicellularity may have evolved.
"We had hypotheses about how multicellularity could evolve, but until now, no one has really been able to test them,” Ratcliff says. "Now that we have this experimental system, we can ask lots of really exciting questions."
As though at one time in the distant past a single cell made a decision about what it wanted for the future after it was gone, offspring. This is really absurd. They put complex thinking and planning into a single cell as though it had a big brain to figure out it's goals and then to design itself to carry them out. I am fed up with the ridiculousness of putting personality and complex thoughts and abilities to carry them out into one cell creatures. The only way a single cell would compete to live and propagate would be if someone who designed it, who did think, put those properties into it.
Rather than look at the whole, consider the parts.
A human started as one cell and grew int a collection of specialized parts and organs. A human is a collection of specialists that live together to function.
The evolutionists make it sound so simple. Matter + Water + Energy + Time = The universe and all living things.
If it were so simple to evolve life why isn’t it just as easy for non-living practical objects to likewise evolve? Why haven’t computers washed ashore that were never manufactured?
Read Darwin’s Black Box by Michael Behe to realize that the “irreducible complexity” of things don’t just happen out of thin air.
That's the way we observe God did it. I don't know why you think it's simple.
If it were so simple to evolve life why isn’t it just as easy for non-living practical objects to likewise evolve? Why haven’t computers washed ashore that were never manufactured?
The key term you use is non-living.
I agree. The author of the article, Sarah Fecht, is still a college student. Social cooperation among individuals of a species can be beneficial to the survival of the species which is what evolution is really about. She's making a common mistake by assuming that survival solely rewards the selfish.
A genome contains information. Where did it come from?
I’m not an evolutionist. I don’t think it is simple.
It is easier to evolve a non-living object that has a practical use than a living object whether it be cellular, plant or animal?
If that which is alive is defined as being capable of metabolism, growth, reproduction, irritability, adaption and movement then where does evolution get its beginning? There are simply too many things to have occurred by accident to account for any living thing.
Let’s look at the other side of the question. Why didn’t God create machines that can “live” on places like the Moon or other places in the Solar System where we don’t see life?
One simple cell communicates to the other, “Why don’t we get together so that we can both function better and our offspring will have a better chance of living. The other says “Good idea, come on over”. The first little cells says “Great” and over he comes, but what happens, chomp, chomp, chomp.
Genesis tells me Who. The origin of Species tells me how.
Just one part is amazing.
But hundreds or thousands of equally amazing parts is astounding.
Now make each INDIVIDUAL part work in perfect sync with all the others-thats nothing short of MIRACULOUS.
:’)
You really trust old Darwin to God's Word that tells us not only who, but how long it took Him to do it. I trust the One who did the creating, who informs me through His Word about the details.
What some Christians do not understand or acknowledge is there is an enemy, Satan, who is over hosts of demons, who is the prince and power of the air. He is able to and keeps many of the people of the earth blinded to truth. He has had 6,000 years to prefect his craft. The institutes of the world are largely under his control. He is a consummate liar and works day and night making sure lies that undercut the glory of God are propagated throughout the world's systems.
You would expect such beliefs as the the belief in evolution, which is contrary to The Word of God, to be accepted in a world held largely under his sway. You would expect the institutes of the world's system to have lies embedded into their very foundations that undermine the truth of the power and glory of God in creation.
The thing the Christian must do who understands this is to be very careful about what is being presented as fact by a basically evil, anti God world system. Believe the Bible first. If you do and honestly investigate you will find myriads of evidence that support Biblical truth, providing of course, you pray and ask God to remove any blinders that the evil one has plastered over the eyes of your soul and you do the research.
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Exodus 20:11 For [in] six days the LORD made heaven and earth, the sea, and all that in them [is], and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.
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1Jo 5:19 [And] we know that we are of God, and the whole world lieth in wickedness.
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2Cr 4:4 In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
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Eph 2:2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:
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Jhn 8:44 Ye are of [your] father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
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