YOU MAY NOT have noticed while you were scarfing your avocado toast, but 2015 was the year of the egg, at least as far as the food industry was concerned. An Avian flu outbreak briefly sent egg prices soaring. Meanwhile, McDonald's, the world's largest fast food chain and one of the biggest egg buyers anywhere, announced it would ditch its conventionally farmed eggs and sell nothing but cage-free eggs in all of its US and Canadian restaurants. By the end of the year, just about every major fast food chain and a handful of multinational food companies had followed suit, including Subway, Starbucks, Nestle and most recently Wendy's, which joined in just this month.

But these announcements had a catch. The companies said the switch to cage-free would take anywhere from five years to a decade to complete. How could it possibly take ten years to let a bunch of chickens out of their cages?

As it turns out, going cage-free requires much more planning, money, and logistical engineering than the seemingly simple notion of setting some hens free would suggest. Ironically, this massive supply chain overhaul stems from consumer demand to return to the egg-producing practices of our pre-industrial past, but without undoing all the positive benefits of scale, affordability, and safety that were achieved through industrialization. It actually took farmers a really long time to figure out how to put the bird in the cage—and it's going to take a while to figure out how to get it back out.

To understand how we got here, let's do some time traveling. Back in the 1920s, chicken egg farmers were pretty small-scale operations. Even the big guys only had about 400, maybe 500, hens, and these birds all just waddled around in the dirt, coo-cooing and laying eggs everywhere. People then had to collect those eggs by hand and clean them manually. Sometimes animals would attack the chickens in the night. Sometimes they attacked each other. Sometimes they stepped in their own waste and got sick, or they hung around with other animals or birds and got sick. Quite a few of them died. Life as a chicken has its risks.