Reference: 157 Title: Endosymbiosis: Cyanobacteria were the Ancestor of Chloroplasts Summary: The endosymbiotic theory posits that chloroplasts evolved from cyanobacteria, supported by evidence like their own DNA and similarities in ribosomes. URL: https://evolution.berkeley.edu/the-history-of-evolutionary-thought/1900-to-present/endosymbiosis-lynn-margulis