> <i>The first occurred about 2.2 billion years ago, when an archaea swallowed a bacterium that became the mitochondria. The second time happened about 1.6 billion years ago, when cells absorbed cyanobacteria that became chloroplasts.</i><p>How was it possible that I could take 3 years of high school biology and not have heard that one lifeform absorbing another lifeform was responsible for these amazing new capabilities? We learned about mitochondria and chloroplasts, but in a very dry way. Primary education could be so much more interesting to kids with context like this.