The Mysterious Kingdom of Protista

What problems do biologists have with the kingdom Protista?

Why did Lynn Margulis and Karlene Schwartz struggle to justify the Protista kingdom?

Answers:

Biologists face challenges with the kingdom Protista due to the presence of undulipodia (flagella) in common ancestors of all phyla, even before mitochondria. While some phyla have all members bearing undulipodia, others do not. This inconsistency in structure raises doubts about the classification of Protista as a kingdom.

Lynn Margulis and Karlene Schwartz, in their book The Five Kingdoms (W.H. Freeman, 1998), put in great effort to justify the Protista (they preferred the term Protoctista) kingdom. They highlighted the presence of undulipodia in common ancestors to all phyla, even before mitochondria, to support their argument. However, they also acknowledged the inconsistency within phyla regarding the presence of undulipodia. This inconsistency in structure poses a challenge for biologists in solidifying the classification of Protista as a kingdom.

The foundation on which the Protista kingdom is built seems to be unstable due to the varying presence of undulipodia among different phyla. While all human cells are ultimately fathered by sperm, which bear undulipodia, it is not accurate to classify humans as protists solely based on this characteristic. This reveals the complexities and debates within the scientific community regarding the classification of organisms.