How can the hypothesis that asserts that chloroplasts as well as mitochondria were primitive prokaryotes that associated in mutualism with primitive anaerobic eukaryotic cells be corroborated?

The explained hypothesis is known as the endosymbiotic hypothesis about the evolutionary origin of mitochondria and choloroplasts.

Mutualism is explained as: mitochondria and chloroplasts can offer energy and nutrients to the cell in exchange for protection. The hypothesis is strengthened as those organelles have their own DNA, RNA and protein synthesis machinery and they separate themselves through binary division like bacteria do.