The first animal eggs were released into the equable oceans, where their outer membrane could be simple and their food supply minimal. Some 300 million years ago, the earliest fully land-dwelling animals, the reptiles, developed a self-contained egg with a leathery skin that slowed fatal water loss, and with enough food to support prolonged embryonic development into a fully formed animal. The eggs of birds, animals that arose some 100 million years later, are a refined version of the primitive reptile egg. Their hard, mineralized shell is impermeable enough that the embryo can develop in the driest habitats; and they contain an array of antimicrobial defenses. These developments made the bird egg into an ideal human food. It contains a sizeable and balanced portion of animal nutrients; and it’s so well packaged that it keeps for weeks with little or no care.