Soru

Read the following passage regarding the history of biological taxonomy.

Prior to the late 1970s, the biological classification of life was dominated by a rigid two-empire dichotomy: eukaryotes, which possess a membrane-bound nucleus, and prokaryotes, which lack one. This morphological paradigm, heavily reliant on microscopic observation, assumed that cellular structure was the most accurate proxy for evolutionary relatedness. Because all known bacteria lacked a nucleus, they were uniformly grouped into the prokaryotic empire, a classification that implied a shared, exclusive evolutionary history distinct from all eukaryotic organisms.

In 1977, Carl Woese and George Fox challenged this entrenched orthodoxy by shifting the basis of classification from cellular morphology to molecular genetics. By sequencing 16S ribosomal RNA—a highly conserved molecule present in all living organisms—Woese discovered that a group of methane-producing microbes, previously classified as bacteria, were as genetically distant from standard bacteria as they were from plants and animals. Woese proposed that these organisms, later named Archaea, represented a distinct third domain of life.

The scientific establishment initially mounted a fierce defense of the bipartite system. Traditionalists, led most notably by evolutionary biologist Ernst Mayr, dismissed Woese’s genetic evidence as insufficient to warrant a taxonomic overhaul. Critics argued that 16S rRNA analysis was an unreliable metric for deep evolutionary divergence, contending instead that the profound morphological distinction between cells with and without a nucleus was the only biologically meaningful dividing line. Furthermore, detractors hypothesized that the genetic peculiarities of methanogens were simply rapid evolutionary responses to extreme environmental conditions rather than evidence of ancient phylogenetic divergence.

Ultimately, the three-domain model prevailed as subsequent biochemical analyses corroborated Woese’s genetic findings. Researchers discovered that, despite their superficial resemblance to bacteria, Archaea possess unique cellular features, including ether-linked membrane lipids and complex RNA polymerases that more closely resemble those of eukaryotes. Additionally, the complete absence of peptidoglycan—a defining structural polymer in bacterial cell walls—cemented the status of Archaea as a fundamentally separate lineage.

According to the passage, the traditionalists who defended the bipartite system of classification relied on all of the following arguments or assumptions EXCEPT: