Friday, August 22, 2008

Design #59- A Lizard That Can Walk on Water

It’s called the Jesus lizard but it’s not a miracle that it walks on water.

Most animals, when attempting to run across water, sink. That’s obvious. However, there is a lizard that lives in Central America called the basilist lizard, a.k.a. the Jesus Christ lizard, or simply the Jesus lizard. It got this name because of its seeming ability to walk on water!
The lizards range in size from less than 0.01 ounces upon hatching to more than 7 ounces as adults. Throughout their growth, they can run across water on their hind limbs at about 5 feet a second for a distance of approximately 15 feet before they sink to all fours and swim. A water strider is one thing, but a lizard? How does it do this?
The Jesus lizards accomplish this by generating forces with their feet that keep their bodies both above the surface and upright. To investigate this, scientists spread glass beads across a table top and, with the use of high speed cameras and computers, were able to study the forces the lizard uses in its stride. They learned the stride is divided into three phases: the slap, the stroke, and the recovery. “During the slap the foot moves primarily vertically downward. During the stroke it moves primarily backward. And during the recovery the foot moves up and out of the water, returning to the start position of the next step.”
“According to analysis of their video, the lizards generate force for support during the slap phase, in which the lizards’ foot plunges straight down, pushing water down and away from the foot while creating a pocket of air surrounding the foot. The support force generated by the slap is sufficient to keep the lizards’ bodies above the water’s surface during the stroke phase in which they propel themselves forward by kicking their leg back through the water.” In other words, unlike land movement which generates spring in the step, this lizard’s foot when on water acts more like a piston, generating its force moving up and down.
To stay upright, the lizards also create forces off to the sides. These are called lateral reaction forces. To create these, “the lizards push outward during the slap phase as they fall toward their supporting limb. Then they pull toward their body during the stroke as their center of mass shifts away from the supporting limb. The effect keeps the lizards upright as long as they are moving.” In summary, the lizard’s ability is very complex!
This study is significant because of the difficulty in making robots that walk like humans. When walking is understood better, then robot movement will improve. Here is another example of reverse engineering, studying creation as a model for invention. That seems to admit the presence of design, doesn’t it? Creationists might ask, why not throw the components for robots together and trust that chance will produce a walking robot? Sounds as logical as evolution, don’t you think?
Source: http://news.nationalgeographic.com/news/2004/11/1116_041116_jesus_lizard.html

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Posted by Jim at 07:39 AM

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