Each cell would perform its own discrete task. But in communicating with the rest, it would form a more complex whole. "This is an almost foolproof way of operating," Kay once told me. Computer programmers could build something large by focusing on something small. That's a simpler task, and in the end, the thing you build is stronger and more efficient.

The result was a programming language called SmallTalk. Kay called it an object-oriented language—the "objects" were the cells—and it spawned so many of the languages that programmers use today, from Objective-C and Swift, which run all the apps on your Apple iPhone, to Java, Google's language of choice on Android phones. Kay's vision of code as biology is now the norm. It's how the world's programmers think about building software.

But Kay's big idea extends well beyond individual languages like Swift and Java. This is also how Google, Twitter, and other Internet giants now think about building and running their massive online services. The Google search engine isn't software that runs on a single machine. Serving millions upon millions of people around the globe, it's software that runs on thousands of machines spread across multiple computer data centers.