The complex cells that make up plants and animals only survive today because their ancestors formed partnerships with bacteria. In a previous post, I wrote about a microbe called Hatena, which provides us with a snapshot of what the early stages of this alliance might have looked like. Hatena swallows an alga which becomes an integrated part of its body.

Millions of years ago, the ancestors of complex cells did the same thing, taking in bacteria and merging with them to form a single creature. Today, these integrated bacteria are mitochondria, which provide us with energy, and chloroplasts, which allow plants to photosynthesise. Hatena and its algal partner show us what the early steps in this vital alliance might have