If life began at conception, Annie would have been 1 year old on Wednesday. Even though I don’t buy that from a public policy standpoint, it’s kind of cool to think about the day her genetic destiny was determined. I liked this paragraph from a neat article on twins:

“At the moment that a sperm penetrates an egg, that single-­cell zygote is what is known as totipotent: It is pure potential. It has in it the makings of an eyebrow’s curve, a heart’s thick muscle, a neuron’s electrochemical power; it has in it the finicky instructional manual that will direct the building of the body’s every fiber and the regulation of those fibers. But that one cell splits into two, and instantly, lights begin to go out, potential dims. In order for that one cell to become a tiny bit of flesh in a heart, and not the hair of an eyebrow, one or more of its genetic signaling pathways must shut down. The result is differentiation, a steady process of elimination that allows complex biological universes to be built. Every time a group of cells divides, each one becomes more like one thing, less like another.”

— “The Mixed-Up Brothers of Bogota,” The New York Times Magazine, July 9, 2015

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