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Why do some biologists no longer consider Protista a valid natural group?

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A herd of African elephants stands at the edge of the Chobe River in Botswana, drinking water with a backdrop of dry hills and scattered green trees. — life A herd of African elephants (*Loxodonta africana*) drinking from the Chobe River, Botswana.

Biologists no longer consider the kingdom Protista a valid natural group primarily because it is paraphyletic. In modern systematics, which prioritizes phylogeny—the evolutionary history of organisms—a valid group must reflect a shared common ancestry.12

The historical classification of protists was based largely on morphology and the exclusion of organisms that did not fit into the kingdoms of Animalia, Plantae, or Fungi. However, advancements in molecular techniques, such as ribosomal RNA sequencing, have revealed that these organisms are highly diverse and do not share a single, exclusive evolutionary origin.134

Instead of forming a single kingdom, various protistan groups are now classified within eukaryotic supergroups alongside multicellular organisms. For example, certain unicellular algae are grouped with plants in the supergroup Archaeplastida, while other protists are placed with animals and fungi in the supergroup Opisthokonta. Because the traditional Protista grouping fails to represent these distinct evolutionary relationships, it is widely abandoned in formal classification.14