What evidence supports the concept of endosymbiosis?

The concept of endosymbiosis is primarily supported by the observation that mitochondria and chloroplasts possess their own ribosomes and can synthesize proteins independently. This similarity to prokaryotic cells, which also have their own ribosomes, indicates that these organelles may have originated from free-living bacteria that entered into a symbiotic relationship with ancestral eukaryotic cells.

This independent protein synthesis is a fundamental aspect of the endosymbiotic theory, suggesting that these organelles retain some autonomy from the host cell's nuclear DNA, thus supporting their evolutionary origin as separate entities that merged with eukaryotic cells.

The presence of their own ribosomes, resembling those found in prokaryotes, provides compelling evidence of their evolutionary lineage, as ribosomal structure and function reflect genetic ancestry. This independence in protein production further strengthens the argument that mitochondria and chloroplasts were once free-living organisms that became vital components of eukaryotic cells through endosymbiotic events.