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ADMIRERS OF CHARLES DARWIN - HELP!
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Topic: ADMIRERS OF CHARLES DARWIN - HELP! (Read 2146 times)
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Bianca
Superhero Member
Posts: 41646
Re: ADMIRERS OF CHARLES DARWIN - HELP!
«
Reply #30
on:
February 25, 2009, 08:17:40 am »
The "living fossil," Platynereis dumerilii.
(Credit:
Maj Britt Hansen,
Photolab,
EMBL heidelberg)
Darwin's Greatest Challenge Tackled: The Mystery Of Eye Evolution
ScienceDaily
(Nov. 1, 2004)
— October 28, 2004
-- When Darwin's skeptics attack his theory of evolution, they often focus on the eye. Darwin himself confessed that it was "absurd" to propose that the human eye evolved through spontaneous mutation and natural selection. Scientists at the European Molecular Biology Laboratory (EMBL) have now tackled Darwin's major challenge in an evolutionary study published this week in the journal Science. They have elucidated the evolutionary origin of the human eye.
Researchers in the laboratories of Detlev Arendt and Jochen Wittbrodt have discovered that the light-sensitive cells of our eyes, the rods and cones, are of unexpected evolutionary origin – they come from an ancient population of light-sensitive cells that were initially located in the brain.
"It is not surprising that cells of human eyes come from the brain. We still have light-sensitive cells in our brains today which detect light and influence our daily rhythms of activity," explains Wittbrodt. "Quite possibly, the human eye has originated from light-sensitive cells in the brain. Only later in evolution would such brain cells have relocated into an eye and gained the potential to confer vision."
The scientists discovered that two types of light-sensitive cells existed in our early animal ancestors: rhabdomeric and ciliary. In most animals, rhabdomeric cells became part of the eyes, and ciliary cells remained embedded in the brain. But the evolution of the human eye is peculiar – it is the ciliary cells that were recruited for vision which eventually gave rise to the rods and cones of the retina.
So how did EMBL researchers finally trace the evolution of the eye?
By studying a "living fossil," Platynereis dumerilii, a marine worm that still resembles early ancestors that lived up to 600 million years ago. Arendt had seen pictures of this worm's brain taken by researcher Adriaan Dorresteijn (University of Mainz, Germany). "When I saw these pictures, I noticed that the shape of the cells in the worm's brain resembled the rods and cones in the human eye. I was immediately intrigued by the idea that both of these light-sensitive cells may have the same evolutionary origin."
To test this hypothesis, Arendt and Wittbrodt used a new tool for today's evolutionary biologists – "molecular fingerprints". Such a fingerprint is a unique combination of molecules that is found in a specific cell. He explains that if cells between species have matching molecular fingerprints, then the cells are very likely to share a common ancestor cell.
Scientist Kristin Tessmar-Raible provided the crucial evidence to support Arendt's hypothesis. With the help of EMBL researcher Heidi Snyman, she determined the molecular fingerprint of the cells in the worm's brain. She found an opsin, a light-sensitive molecule, in the worm that strikingly resembled the opsin in the vertebrate rods and cones. "When I saw this vertebrate-type molecule active in the cells of the Playtnereis brain – it was clear that these cells and the vertebrate rods and cones shared a molecular fingerprint. This was concrete evidence of common evolutionary origin. We had finally solved one of the big mysteries in human eye evolution."
--------------------------------------------------------------------------------
Adapted from materials provided by European Molecular Biology Laboratory.
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MLA European Molecular Biology Laboratory (2004, November 1). Darwin's Greatest Challenge Tackled: The Mystery Of Eye Evolution. ScienceDaily. Retrieved February 25, 2009, from
http://www.sciencedaily.com
/releases/2004/10/041030215105.htm
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Bianca
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Posts: 41646
Re: ADMIRERS OF CHARLES DARWIN - HELP!
«
Reply #31
on:
February 25, 2009, 08:23:48 am »
Worker ants of the world, unite! You have nothing to lose but your fertility.
(Credit:
iStockphoto/
Mark Evans)
«
Last Edit: February 25, 2009, 08:24:48 am by Bianca
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Bianca
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Posts: 41646
Re: ADMIRERS OF CHARLES DARWIN - HELP!
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Reply #32
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February 25, 2009, 08:27:00 am »
Darwin Was Right About How Evolution Can Affect Whole Group
ScienceDaily
(Nov. 20, 2008)
— Worker ants of the world, unite! You have nothing to lose but your fertility. The highly specialized worker castes in ants represent the pinnacle of social organization in the insect world. As in any society, however, ant colonies are filled with internal strife and conflict. So what binds them together? More than 150 years ago, Charles Darwin had an idea and now he's been proven right.
Evolutionary biologists at McGill University have discovered molecular signals that can maintain social harmony in ants by putting constraints on their fertility. Dr. Ehab Abouheif, of McGill's Department of Biology, and post-doctoral researcher, Dr. Abderrahman Khila, have discovered how evolution has tinkered with the genes of colonizing insects like ants to keep them from fighting amongst themselves over who gets to reproduce.
"We've discovered a really elegant developmental mechanism, which we call 'reproductive constraint,' that challenges the classic paradigm that behaviour, such as policing, is the only way to enforce harmony and squash selfish behaviour in ant societies," said Abouheif, McGill's Canada Research Chair in Evolutionary Developmental Biology.
Reproductive constraint comes into play in these ant societies when evolutionary forces begin to work in a group context rather than on individuals, the researchers said. The process can be seen in the differences between advanced ant species and their more primitive cousins. The study was published in the Nov. 18 edition of the Proceedings of the National Academy of Sciences.
Ants – organized in colonies around one or many queens surrounded by their specialized female workers – are classic examples of what are called eusocial organisms.
"More primitive, or ancestral, ants tend to have smaller colony sizes and have much higher levels of conflict over reproduction than the more advanced species," Abouheif explained. "That's because the workers have a much higher reproductive capacity and there is conflict with the queen to produce offspring."
To their surprise, Khila and Abouheif discovered that "evolution has tinkered with the molecular signals that are used by the egg to determine what's going to be the head and what's going to be the tail, to stop the worker ants from producing viable offspring," Abouheif explained. "Different species of ants have different levels of this "reproductive constraint," and we believe those levels provide a measure of how eusocial the colony is. The less the workers reproduce, the more coherent the group becomes."
The existence of sterile castes of ants tormented Charles Darwin as he was formulating his Theory of Natural Selection, and he described them as the "one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory." If adaptive evolution unfolds by differential survival of individuals, how can individuals incapable of passing on their genes possibly evolve and persist?
Darwin proposed that in the case of ant societies natural selection applies not only to the individual, because the individual would never benefit by cutting its own reproduction, but also to the family or group. This study supports Darwin's prescient ideas, and provides a molecular measure of how an entire colony can be viewed as a single or "superorganism."
--------------------------------------------------------------------------------
Adapted from materials provided by McGill University.
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MLA McGill University (2008, November 20). Darwin Was Right About How Evolution Can Affect Whole Group. ScienceDaily. Retrieved February 25, 2009, from
http://www.sciencedaily.com
/releases/2008/11/081119122634.htm
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Bianca
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Re: ADMIRERS OF CHARLES DARWIN - HELP!
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Reply #33
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March 01, 2009, 08:42:55 am »
ARTICLES IN NY TIMES
http://www.nytimes.com/interactive/2009/02/09/science/20090209-darwin-evolution-documents.html?ref=science
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