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From NYTimes: "Our bodies start out symmetrical, the left side a perfect reflection
of the right. “Visible signs of left-right asymmetry in the human body are apparent around six weeks,” said Sudipto
Roy of the Institute of Molecular and Cell Biology in Singapore, an author of a review of left-right asymmetry that was published
last week in the journal Open Biology. The heart shows the first
visible asymmetry. Starting out as a simple tube, it loops to the left. The heart then starts to grow different structures
on each side, producing the chambers and vessels required to pump blood.
Meanwhile, other organs start moving. The stomach and liver each move clockwise away from the midline of the embryo. The large
intestines sprout an appendix on the right. The right lung grows three lobes, the left only two. But these visible changes arise long after the embryo has developed differences on its left and
right. Experiments have revealed that the early embryo produces different proteins on each side while it still looks symmetrical."
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