Tristan Payne

Protista Evolutionary History

A large amount of evidence shows that protists sundry characteristics are derived from endosymbiosis.

This evidence suggests that one lineage of heterotrophic eukaryotes acquired and additional

endosymbiont- a photosynthetic cyanobacterium- that eventually evolved into plastids. This plastid-

bearing lineage then gave rise to red and green algae. The credible foundation for this hypothesis is that

the DNA of plastid genes in red and green algae is very similar to the DNA of cyanobacteria. The red and

green algae underwent secondary endosymbiosis on a number of occasions in which they were ingested

in the food vacuole of heterotrophic eukaryotes and then became endosymbionts. An example of this is

when protists known as chlorarachniophytes evolved when a heterotrophic eukaryote engulfed a green

algae. The fact that their plastids are surrounded by four membranes (The two inner originated as the

inner and out of ancient cyanobacterium; the third derived from the engulfed algae’s plasma

membrane; and the outermost derived from the heterotrophic eukaryote’s food vacuole) is consistent

with the hypothesis that chlorarachniophytes evolved from a eukaryote that engulfed another

eukaryote.