You Started as One Cell. It Had No Idea Where to Put Your Eyes.
You were once a cell.
Round, soft, no eyes, no heart, no brain. It did one thing: divide. One into two, two into four. At the eight-cell stage, the embryo compacts. Outer cells get squeezed outside, inner cells get enclosed. At first, inside and outside are not predetermined. Squeezing creates the difference. Outer cells have apical-basal polarity. Inner cells lose the apical region. Different positions, different signals, gene programs begin to diverge.