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light down to low levels, and 6 million cones to detect color and fine detail. The aperture of the iris automatically widens or narrows to let in more or less light, allowing us to see in both bright daylight and dim starlight. The really intriguing part of our sight is the image processing the brain uses to make sense of the visual data from the eyes. In our brain, billions of neurons are connected to each other through innumerable paths and connections. Visual signals are transmitted from the retina to the brain by electrical impulses traveling over sensory neurons. As we scan a scene, the brain collects multiple snapshots and blends them, discarding any blurry images and automatically balancing the scene by brightening dark areas and darkening light areas, allowing us to clearly see both bright and shaded areas. Then it blends the left and right data streams to paint a comprehensive mental picture of the scene in front of us. This picture has its colors adjusted to compensate for differences in lighting, and it includes depth information, very bright and very dark zones, and ten million colors. Hands are another fascinating human feature. They are deft Most of the muscles that control the fingers are in the forearm, connected to the fingers through an amazing system of bones and tendons. manipulators and delicate touch sensors, yet they also have a strong grasp. To keep the fingers slender and dexterous, but still strong, most of the muscles that control them are in the forearm, connected to the fingers through an amazing system of bones and tendons. This system works so well that experienced rock climbers can support their entire body weight on one finger, a pianist can play many notes per second with each hand, and a good typist can type a hundred words a minute. The amazing design for our eyes and hands is embedded in the DNA-containing chromosomes within each cell of our bodies. From the moment of conception, the DNA of a growing baby includes the in- Loaves & Fishes • Issue 32 | 19


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