The Endosymbiotic Theory

The Endosymbiotic Theory suggests that complex cells, called eukaryotes (like plants and animals), originated from simple cells, called prokaryotes (like bacteria). Around 1.5 billion years ago, larger prokaryotic cells engulfed smaller ones but didn't digest them. Instead, these smaller cells entered into a mutually beneficial relationship, eventually evolving into specialized parts of the larger cell, such as mitochondria and chloroplasts. This theory explains how eukaryotic cells came to have their own energy-producing and photosynthetic capabilities, highlighting the cooperative interactions that can drive evolution and complexity in life forms.