Phylogeny The phylogeny of Giardia is unclear, but two main theories exist. Firstly, Giardia may be extremely primitive eukaryotes that branched off early from other members of their group. This theory is supported by several features: their lack of complete mitochondria (see Characteristics) and other organelles, their primitive metabolic pathways, and their position on a phylogenetic tree. However, many of these differences have been refuted in recent years, and many researchers are supporting a second theory: that Giardia are highly evolved parasites, which have lost ancestral characteristics.
pHYloGeny tHe PhylogENY Of GIArDiA iS UNCLear, but two mAin thEOrIEs eXISt. FirSTlY, giArdia May BE extREmely PrImiTIve eukaryoTEs ThAT brAncHed OfF eArly fROm otHER mEmBers of tHeIR GRouP. THIs ThEorY IS sUpported bY severAl FeatUreS: their lAck of complEte mitocHondRIA (see chaRaCteriSTiCs) and oTHeR oRgAnelLES, TheiR priMitIVE MetAboLic patHways, and theiR POsition oN A phYlogENetic tree. howevEr, MAny of These difFeReNcES havE beEn refuTed in REcENT yEaRS, And Many rESEarChers arE suPPOrtInG A secOnd tHeory: That giArdia are hIGHly evolvED parasIteS, whicH Have lost aNcESTral cHAractErISticS.