Proto- is a prefix meaning “first” or “earliest” that we attach to the beginning of words to describe something that came before, or an early version of something else.

Scientists use proto- constantly. A protocontinent is a landmass that existed before our modern continents formed. Proto-Germanic is the ancient language that evolved into German, English, Dutch, and other languages we speak today. When astronomers discovered a swirling disk of dust and gas around a young star, they called it a protoplanetary disk because planets would eventually form from it.

You can think of proto- as meaning “the ancestor of” or “the original version of.” A prototype is the first working model of an invention, built before mass production begins. The Wright brothers' earliest airplane was a prototype for all the aircraft that followed. When engineers design a new video game console or smartphone, they build prototypes first to test whether their ideas actually work.

When you see proto- attached to a word, you know you're learning about something foundational, something that came first and led to what exists now.