Originally published November 7, 2007 at 12:00 AM | Page modified November 7, 2007 at 2:05 AM
Scientists track early evolution of sight to hydras
Scientists have traced the origin of eyes back to a transparent blob of living jelly floating in the sea about 600 million years ago. That creature, the distant...
McClatchy Newspapers
WASHINGTON — Scientists have traced the origin of eyes back to a transparent blob of living jelly floating in the sea about 600 million years ago.
That creature, the distant ancestor of a modern freshwater animal known as a hydra, could only distinguish light from dark.
But that was such an advantage that it was passed on from generation to generation of the hydra's cousins and their myriad descendants. It was the precursor of the wildly different, ever more complex eyes of fish, ants, flies, giraffes and people.
The hydra work was reported last month in the journal PLoS ONE by biologists David Plachetzki and Todd Oakley, of the University of California, Santa Barbara.
It helps solve one of the puzzles of Darwinian evolution, the process by which a complex organ such as an eye could arise by random genetic mutations and natural selection.
"These results are significant in advancing our understanding of the early evolution of sight in animals," said Jerry Cook, a program director at the National Science Foundation, which financed the work.
In their research, Oakley and Plachetzki discovered that a gene, opsin — after the Greek word "ops," meaning "eye" — exists in hydras but not in sponges, an even more primitive animal.
The scientists calculated that opsin genes appeared about 600 million years ago, because that's when the evolutionary branch that led to modern hydras split from the line that led to sponges.
Opsin genes direct the production of light-sensitive proteins, also called opsins, that coat the surface of a hydra, especially around the mouth. The opsin proteins would help these simple animals tell night from day and perhaps help them find food.
"Hydra probably uses its light sensitivity to find prey," Oakley said.
According to Oakley, the opsin proteins must have evolved from earlier "signaling" proteins that send chemical messages to other proteins. Signaling proteins exist in all living creatures, from single-celled bacteria to humans.
Other biologists commended Oakley's work. "It makes sense that oceangoing animals such as [the hydra's ancestors] would use light detection to orient themselves or regulate a body clock," said Sean Carroll, an evolutionary geneticist at the University of Wisconsin, Madison.
Copyright © 2007 The Seattle Times Company
UPDATE - 10:01 AM
Rebels tighten hold on Libya oil port
UPDATE - 09:29 AM
Reality leads US to temper its tough talk on Libya
UPDATE - 09:38 AM
2 Ark. injection wells may be closed amid quakes
Armed guards save Dutch couple from Somali pirates
Navy to release lewd video investigation findings

- Lakewood cop accused of embezzling $150K meant for slain officers' families
- 3 big health insurers stockpile $2.4 billion as rates keep rising
- Agency set to investigate handling of 911 call about Josh Powell
- Quick decisions: How Washington hired its new football staff
- Historic day for gay marriage as another fight looms
- Justin Wilcox's versatile defensive style is the right fit for Huskies | Jerry Brewer
- Social worker recounts minutes before Powell fire
- It's Terrence Time: Enigmatic Ross leads Huskies
- $25B settlement reached over foreclosure abuses
- Club promoter convicted in brutal 2010 murder of Des Moines prostitute
- Gay-marriage bill passes House, awaits Gregoire's signature
471 - Historic day for gay marriage as another fight looming
359 - Wanted in Seattle classrooms: more teachers of color
291 - 3 big health insurers stockpile $2.4 billion as rates keep rising
243 - Source: NY, California to sign mortgage settlement
231 - Oregon live game thread
155 - Council members get briefing on arena proposal, minus details
143 - Pac-12 picks ... including the UW game
140 - AP Source: Obama to change birth control rule
129 - Worker: Josh Powell told son he had 'surprise'
101
- State Medicaid program to stop paying for unneeded ER visits
- 3 big health insurers stockpile $2.4 billion as rates keep rising
- Wanted in Seattle classrooms: more teachers of color
- One man's audacious pursuit of sailing history
- Darren Berg gets 18-year sentence for Ponzi scheme
- $25B settlement reached over foreclosure abuses
- Economy, blogs give survivalists new reason to look to Northwest
- State's share of mortgage settlement: $648 million
- Bellevue College adds a third bachelor's degree program
- 'Gauguin and Polynesia': dazzling mix-and-match | Art review



