Large toggle switch, depicted in circuit 'open...

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Twins are what caused scientists to look beyond our genetics. Twins clearly have identical genes but often result in two very different people. One may be heavy while the other is slim. One may get cancer while the other doesn’t. This difference seemed to point to something acting outside of our genes. That something is epigenetics. When I was a child I experimented with simple electrical circuits that allowed me to throw different switches to get different patterns of lights. Our genes are like the wiring and light bulbs of those circuits and our epigenetics are very similar to the switches. The hard wired circuit can do different things depending on how the switches are thrown. Our genes can do very different things depending on how our epigenetic switches are thrown. This video shows how this happens in twins as they age.