ENIGMA. “The death effectors that operate in protozoans are still enigmatic and furthermore there exist also protozoans that cannot undergo an apoptosis-like phenotype. It has to await clarification whether the death machinery was lost by reductive evolution, or whether those species without apparent self destruction mechanisms represent an early phylogenic life form.”
http://mcb.berkeley.edu/courses/mcbc245/MCBC245PDFs/Jan31/Huettenbrenner2003.pdf