When Eldad Tzahor cut a small piece of tissue from the front end of a chicken embryo and placed it on a glass laboratory dish, he intended to observe, as he had before, how the head develops. He would watch the scrap of tissue grow and change from a mass of anonymous cells into well-defined facial muscles. But what he saw over the next 2 days, as the cells dutifully began to divide and specialize, was a complete surprise.
Instead of facial muscles, a tiny heart took shape on his dish. Then, the heart began to beat.
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