FRAGMENT FROM NATURE. We have journeyed in this string of ideas from mosaicism the individual to division of labor and outsourcing of functionality. Now it continues with evolutionary bolt-ons that are inherited. The endosymbiotic origin of the nucleus, chloroplasts, mitochondria and other organelles may seem improbable. Symbiogenesis theory by Lynn Margulis (1967) proposed that mitochondria and chloroplasts arose by hereditable symbiosis in a huge saltation. Why did it stop there? Or did it?