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Sioux Falls Scientists endorse Inside the Eye for exposing the
absolute ignorance of those advocating Intelligent Design.
This is an excellent article in a highly reputable science magazine
explaining how eyes evolved and how they work.

Inside the Eye
Nature’s Most Exquisite Creation
By Ed Yong

Inside the Eye (February, 2016) - 28 pages
Inside the Eye at NationalGeographic.com

Click on the link above to get the full story from its source

To understand how animals see, look through their eyes.

IF YOU ASK PEOPLE WHAT ANIMAL eyes are used for, they’ll say: same thing as human eyes. But that’s not true. It’s not true at all.”

AROUND 540 MILLION YEARS AGO, the ancestors of most modern animal groups suddenly appeared on the scene, in an outburst of speciation known as the Cambrian explosion. Many of these pioneering creatures left fossils behind. Some are so well preserved that scientists have been able to use scanning electron microscope images to piece together their inner anatomy, eyes included, and reconstruct their owners’ view of the world.

THE RISE OF EYES

The diversity of eyes in the animal world illustrates how natural selection can transform simple structures that respond to light into camera-like eyes composed of multiple parts working in tandem. Dan-Eric Nilsson at Lund University in Sweden categorizes the development of eyes into four stages—an evolution that theoretically could occur in less than half a million years.

VISUAL TASKS

  • NONDIRECTIONAL PHOTORECEPTION
    Organisms that sense light but not where it’s coming from can regulate circadian rhythms and respond to shadows.
  • DIRECTIONAL PHOTORECEPTION
    Animals move toward or away from light to orient their bodies and trigger alarm responses to predators.
  • LOW-RESOLUTION VISION
  • Organisms that have developed low-resolution eyesight can detect their own motion, avoid objects, and find preferred habitats.
  • HIGH-RESOLUTION VISION
    The most advanced eyes help animals perform complex tasks like selecting mates and recognizing predators and prey.

ADAPTATIONS

  • NONDIRECTIONAL PHOTORECEPTION
    The emergence of just a few photoreceptor cells is a fundamental development that allows simple organisms to react to light.
  • DIRECTIONAL PHOTORECEPTION
    Organisms that develop screening pigment, which partly shades their photo­receptors, can tell where light is coming from.
  • LOW-RESOLUTION VISION
    Cup-shaped eyes with more receptors or compound eyes with additional cups can produce crude images of objects.
  • HIGH-RESOLUTION VISION
    Evolved sensory structures such as lenses, corneas, and irises focus light on photo­receptors, creating images with higher resolution.

NILSSON’S MODEL SHINES fresh light on an old debate: whether eyes evolved once or many times. The legendary German evolutionary biologist Ernst Mayr claimed that eyes had between 40 and 65 independent origins, because they came in so many distinct shapes and forms. The late Walter Gehring, a Swiss developmental biologist, argued that eyes evolved just once, after he discovered that the same master gene—called Pax6—controls eye development in virtually every creature with eyes.

Eye of the Beholder

  • Flatworm
    Flatworm eyes consist of small cups of photoreceptor cells that are able to determine which direction light is coming from. The worms need this cue to identify an appropriate habitat—one that’s shaded from the sun.
  • Box jellyfish
    The box jellyfish has no brain to interpret sensory data, but it can react to simple, low-resolution images. Four lensed eyes look upward to sense mangrove shade where food is abundant. Four other lensed eyes look down through its own transparent body, to help avoid obstacles below.
  • Elephant hawk moth
    The elephant hawk moth’s large pupils let in abundant light, allowing it to discriminate colors even by the dim light of the stars on a moonless night. Thus guided, the nocturnal creature can find nectar in flowers whose colors are undetectable at night by human eyes.
  • Cat
    The eyes of domestic cats have more low-light-sensitive rods than humans and slit pupils that can open wide in the dark, making it easy for them to hunt small animals at night. With fewer color-sensitive cones, however, cats can’t differentiate between greens and reds.
  • Bald eagle
    For eyes with exceptionally high resolution (2.5 times that of human eyes), look to the bald eagle. And while human retinas have one region with a high density of receptors, eagles have two, allowing them to see straight ahead and to the side simultaneously.

OPSINS, LENSES, AND EVERY other component of the eye are all testament to evolution’s patchwork tinkering. It constantly puts existing materials to new functions, and cobbles simple structures together into complex ones. But evolution has no foresight. Once it has trundled down a particular course, it can’t start from scratch again, so its works are always blighted by imperfections. Nilsson is particularly underwhelmed by compound eyes. Their structure, composed of many repeating units, sets an unforgiving ceiling on their visual resolution. If a fly wanted to see with the same resolution as a human, its eye would need to be a meter wide.

AT THE UNIVERSITY OF MARYLAND, Baltimore County, Tom Cronin peers into an aquarium tank, and two googly compound eyes, like muffins mounted on stalks, peer back at him. “Mr. Googles,” as Cronin affectionately calls him, is a gorgeous animal, bedecked in a kaleidoscopic coat of peach, white, green, and blood-red. He is a mantis shrimp—one of a group of crustaceans named for the quick-punching arms protruding beneath their heads, like those of praying mantis. Mr. Googles’s arms end in formidable hammers, which unfurl with such speed and force that they can shatter seashells and aquarium glass.

The mantis shrimp’s eyes have three separate regions that focus on the same narrow strip of space, providing depth perception without help from the other eye. They can also see ultraviolet parts of the spectrum that are invisible to us, and polarized light that vibrates in a single plane. And while we have 3 kinds of color receptors in our retinas, Cronin discovered that mantis shrimps have 12, each tuned to a different color. “It didn’t make sense. None of it did,” he recalls.

2-27-16 The eyes of the animal kingdom
The eyes of the animal kingdom
The eyes of the animal kingdom are endlessly diverse. Why so much variety? you ask people what animal eyes are used for, they'll say: same thing as human eyes. But that's not true at all. In his lab at Lund University in Sweden, Dan-Eric Nilsson is contemplating the eyes of a box jellyfish. Nilsson's eyes, of which he has two, are ice blue and forward facing. In contrast, the box jelly boasts 24 eyes, which are dark brown and grouped into four clusters, called rhopalia. Nilsson shows me a model of one in his office: It looks like a golf ball that has sprouted tumors. A flexible stalk anchors it to the jellyfish. "When I first saw them, I didn't believe my own eyes," says Nilsson. "They just look weird." Four of the six eyes in each rhopalium are simple light-detecting slits and pits. But the other two are surprisingly sophisticated; like Nilsson's eyes, they have light-focusing lenses and can see low-resolution images. Nilsson uses his eyes to, among other things, gather information about the diversity of animal vision. But what about the box jelly? It is one of the simplest animals, just a gelatinous, pulsating blob with trailing bundles of stinging tentacles. It doesn't even have a proper brain — merely a ring of neurons running around its bell. What information could it possibly need? (Webmaster's comment: The Creationists are incredibly ignorant. Their claim that eyes are too complex to evolve completely ignores the 100's of variations of eyes that have evolved over time from simple light sensors to those more complex than ours.)

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Inside the Eye
Nature’s Most Exquisite Creation
By Ed Yong

Sioux Falls Scientists endorse Inside the Eye for exposing the
absolute ignorance of those advocating Intelligent Design.
This is an excellent article in a highly reputable science magazine
explaining how eyes evolved and how they work.