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Why did Carl Woese propose the three-domain system?

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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.

Carl Woese proposed the three-domain system to replace the traditional two-lineage view of life—which categorized organisms simply as eukaryotes or prokaryotes—because his research revealed that prokaryotes actually consist of two distinct, evolutionarily separate groups.12

By analyzing ribosomal RNA sequences, Woese discovered that the organisms previously grouped together as prokaryotes were fundamentally different in their genetic and biochemical makeup. He identified a unique group of microorganisms, which he named Archaea, that were distinct from true Bacteria.1342

This system shifted biological classification from a focus on morphology (physical characteristics and nutrition) to phylogeny (evolutionary history). Woese’s molecular approach provided a more accurate reflection of the evolutionary relatedness of organisms, ultimately demonstrating that Archaea are more closely related to eukaryotes than to bacteria.4123