A boom in affordable housing in the 1950s was helped by the invention of a distinctive multifunctional piece of equipment: the backhoe. Its strong yet relatively slender articulated arm allowed precise yet rapid placement for digging or lifting. The manipulative device is trim and fast, since hoses transfer power to it from a powerful hydraulic pump within the main chassis.

The “arm” of the backhoe makes many people think the equipment design is similar to a human arm, but what makes it so versatile is that it is actually more like a giant human finger. If a valuable piece of equipment mimicking just one finger can be so useful, what capability is possible in a real human hand?

The Formation of Hands

That capability begins as an embryo reaches the end of the fourth week of gestation. A special patch of tissue on the budding limbs stimulates invading cartilage cells to become templates for future bone. Other signals induce muscle-forming cells to develop a muscle mass in the arm and hand. These masses automatically subdivide into twelve muscles of the forearm that act on the wrist and fingers, and nineteen intrinsic muscles of the hand that manipulate only fingers.

The hands are initially flat plates, with the cells making vital internal structures of fingers. The skin cells between fingers undergo a programmed cell death, allowing the formation of five separate digits arranged in the uniquely human hand pattern–right from the start. Muscular ability develops fast. By sixteen weeks an embryo can firmly grip a small rod, and at six months the fetal grip is so tight that he can be lifted by it….

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