Bekijk volle/desktop versie : Zelfmoord, sex en andere zaken in evolutie



21-03-2011, 12:49
Inleiding
Onderstaand artikel snijdt een aantal punten aan mbt evolutie en "nut".

Ondanks dat het gaat om ééncellige organismen, laat het zien dat deze organismen "samenwerken", of in ieder geval invloed op elkaar hebben.

University of Arizona researchers study evolution through single-cell sacrifices of algae[/SIZE]

(bron: therepublic.com)
TUCSON, Ariz. — Some single-celled algae are programmed to commit suicide in a fashion that provides ingredients for their fellow cells to thrive.

This example of altruism is a unique finding in the biological world, where you would expect the forces of natural selection to induce a more dog-eat-dog attitude.

Rich Michod, a University of Arizona evolutionary biologist and philosopher, says the results of such studies are changing our views of the evolutionary process.

In experiments detailed in the February edition of The American Naturalist, authors Pierre Durand, Armin Rashidi and Michod found that cells of the algae Chlamydomonas reinhardtii will go into a programmed death spiral when stressed by heat.

"They chop up their DNA in a very regular pattern. It's called DNA laddering," said Michod.

The phenomenon, known as programmed cell death, is beneficial to neighboring single cells of algae, which end up swimming in usable bits of genetic material instead of deadly toxins.

When instantly killed with sonic waves, the algae "just spewed their guts," said Michod, creating a deadly environment for other cells.

For Michod, the experiment is just one more piece of evidence for an evolving theory that cooperation contributes to critical crossroads in the development of individuals.

Michod and his students and collaborators at the UA Department of Ecology and Evolutionary Biology have studied algae for a decade.

The scientific notions of cooperation have changed in that time and have changed completely since his own college days, said Michod.

Back then, scientists held a simpler view of evolution — at least when it came to lower forms of life.

They knew the human species cooperated to grow food, protect itself and build cities and societies. They had observed cooperation in beehives, ant colonies and termite mounds.

But mostly, our theories of Darwinian processes focused on how the most able competitors survived to pass on their genes.

Turns out that's mostly not the case when you look more deeply, in this case at microscopic cells of pond scum, and even more deeply at the genetic material that makes them what they are.
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"Every organism is really a society," said Michod. "We are a society of cells, and the cells in our bodies are societies of genes. Cooperation is now center stage in our understanding of evolution. [/SIZE]The traditional view of Darwinism is 'nature, raw in tooth and claw' with competition driving everything. Now we see that cooperation is fundamental to the diversity of life."

Michod, chairman of the department, has been at the UA for 30 years and for the last 10 has studied volvocine algae, luring students from studies of squirrels and porpoises to the joys of looking through a microscope at algae.

Graduate student Deborah Shelton said she had lots of fun studying cooperation among porpoises on field studies in New Zealand while earning her master's degree at Texas A&M University, but it is easier, and potentially more rewarding, to study algae, she said.

She read one of Michod's books, "Darwinian Dynamics," and decided his was a good lab in which to study competition, despite the obvious charisma gap between porpoises and pond scum.

"The algae have quite a charm of their own," she said. "They are really fun to watch under the microscope — really mesmerizing."

They also reproduce quickly and don't have the protections afforded animal subjects, she said.

"There is a lot to be said for things with short generation times, and there are no forms to fill out if you want to kill thousands of them."

Algae, which exist in form from single cell to complex colonies, provide researchers a chance to test how they may have evolved over hundreds of millions of years, said Matt Herron, a former graduate student of Michod's who is now a researcher in the Department of Zoology at the University of British Columbia.

He compared their utility to fruit flies. "We've learned a lot more about genetics from fruit flies than we have from mice and rats," he said.

Herron said Michod was a "hands-off" adviser, who was, nevertheless, always available for consulting.

"We got to focus on our particular projects and questions. Rick is really good at looking at things in the bigger picture and how your project fits in with larger theoretical questions."

Those larger questions have kept Michod interested in algae through a decade of supervising research projects in his lab.

The myriad experiments, mathematical models and genotyping his lab has done coalesce into theories about [SIZE="3"]how cooperation aids the major transitions in evolution - from genes to cells, from single cells to more complex ones and on to multi-celled organisms that evolve from asexual to sexual reproduction.

Michod thinks all of these steps can be achieved through cooperative processes.

"You don't need a brain or nervous system to be cooperative," he said.

Programmed cell death in single cells, for example, may be a precursor to multi-cellular life.

Evolution to sexual reproduction seems costly in terms of the energy required but may have the benefit of repairing, rather than blindly reproducing, genetic defects.

We become increasingly complex individuals through these many steps over the eons, said Michod.

21-03-2011, 12:55


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22-03-2011, 09:05

Citaat door Simcha:
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