It all began with a single cell. In the course of almost four billion years, this one cell evolved into the diversity of life that exists on the planet today. We have been able to classify and give a name to around 1.8 million species so far, but there are in fact many more species that no one has ever seen. Estimates range from 10 million to 100 million. But however many forms of life there are, thanks to Charles Darwin we now know that every single one of them shares a common origin.
