(The Atlantic) – Just about every time an embryo implants and begins to grow, it dispatches bits of itself into the body housing it. The depositions begin at least as early as four or five weeks into gestation. And they settle into just about every sliver of our anatomy where scientists have checked—the heart, the lungs, the breast, the colon, the kidney, the liver, the brain. From there, the cells might linger, grow, and divide for decades, or even, as many scientists suspect, for a lifetime, assimilating into the person that conceived them. They can almost be thought of as evolution’s original organ transplant, J. Lee Nelson, of the Fred Hutchinson Cancer Center in Seattle, told me. Microchimerism may be the most common way in which genetically identical cells mature and develop inside two bodies at once. (Read More)