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#69288 - 05/30/03 07:03 AM How to see shells on the sea floor  
Joined: Oct 1999
Posts: 52,996
Marty Offline
Marty  Offline
http://www.nature.com/nsu/030512/030512-14.html

How to see shells on the sea floor
Southeast Asian water babies have supreme aquatic vision.
16 May 2003
HELEN R. PILCHER

In the sea, most of us are half-blind - but the Moken are king. This Southeast Asian tribe of sea gypsies can see twice as clearly underwater as Europeans, researchers have found.

The semi-nomadic Moken, who have settled on Thailand's Surin Islands, use their superior visual skills to dive for food on the ocean floor. It's not known whether the ability is learned or genetic.

Most of us see blurred images when we dive without goggles or a mask. The eye is adapted to air, and struggles to focus light under water. But Moken children can pick out small shells, clams and sea cucumbers at depths of three to four metres.

Moken children can distinguish underwater objects less than 1.5 millimetres wide; Europeans struggle to make out anything less than 3 mm across1, biologist Anna Gislén of Lund University, Sweden, and her colleagues found.

"They use the optics of the eye to the limits of what is [humanly] possible," says Gislén. The team compared the sub-aqua vision of native Moken and holidaying European kids, aged 7-14 years.

Unlike visiting children, the Moken swimmers constrict their pupils while diving, the team found. They can also squeeze their eyes' lenses more, making them thicker and better able to bend incoming light. The two processes bring blurry images into sharper focus, explains Gislén.

"This is the first report I have ever seen about underwater divers and vision," says neurobiologist Howard Howland of Cornell University in Ithaca, New York. "It could be a learned response, albeit totally unconscious," he suggests. Alternatively, evolution may have favoured those with genetic adaptations for better underwater vision.

The ability to squeeze the lens like this is normally weak in children under ten, and strong in adults, says Howland. The underwater abilities of Moken grown-ups remain unknown. "We couldn't test the adults," explains Gislén. "They're too shy."


References
Gislen, A. et al. Superior underwater vision in a human population of sea gypsies. Current Biology, 13, 833 - 836, (2003). |Article|


© Nature News Service / Macmillan Magazines Ltd 2003

#69289 - 05/31/03 09:01 AM Re: How to see shells on the sea floor  
Joined: Jun 2002
Posts: 278
Mel S Offline
 
Mel S  Offline
In a big circle, these iselanders are going back to the mother ocean.......Isn't there are a theory that bottle dolphins lived on the land, and opted to re-adapt to the ocean ? Best-Wishes, Mel S......"Almost going back to Belize !"


Mel Sinderman
#69290 - 05/31/03 10:11 AM Re: How to see shells on the sea floor  
Joined: Mar 2001
Posts: 10,974
klcman Offline
.
klcman  Offline
back to the mother ocean, indeed.

I've always found it fascinating that the % of salt in the human body is exactly the same % as found in our oceans.


_ _ _ _ _ _ _________________ _ _ _ _ _ _
But then what do I know, I am but a mere caveman
#69291 - 05/31/03 11:11 PM Re: How to see shells on the sea floor  
Joined: Jan 2003
Posts: 2,675
dbdoberman Offline
.
dbdoberman  Offline
klc, we are all naturally "pickled"

thanks Marty, that was fascinating - if it is a learned response, wish somebody would teach it to me.

#69292 - 05/31/03 11:59 PM Re: How to see shells on the sea floor  
Joined: Mar 2001
Posts: 10,974
klcman Offline
.
klcman  Offline
better pickled than salt encrusted, huh db? wink


_ _ _ _ _ _ _________________ _ _ _ _ _ _
But then what do I know, I am but a mere caveman
#69293 - 06/01/03 12:10 AM Re: How to see shells on the sea floor  
Joined: Jan 2003
Posts: 2,675
dbdoberman Offline
.
dbdoberman  Offline
salt encrusted.......ARRRRRGGGGHHHHHH!!!! frown


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