Soru

Biologists have long classified terrestrial life into three distinct domains: Bacteria, Archaea, and Eukarya. For decades, the orthodox view, rooted in the pioneering ribosomal RNA sequencing developed by Carl Woese in the 1970s, maintained that these three domains diverged from a single, universal common ancestor early in evolutionary history. This model created a neat, tripartite phylogenetic tree, wherein eukaryotes constitute a distinct lineage that is as ancient as the other two. According to this traditional paradigm, the complex traits characteristic of eukaryotic cells—such as the nucleus, the cytoskeleton, and various membrane-bound organelles—evolved gradually and independently along the eukaryotic branch.

However, the advent of whole-genome sequencing in the late twentieth and early twenty-first centuries has severely complicated this elegant picture, revealing widespread and frequent lateral gene transfer among microorganisms. This realization prompted some evolutionary biologists to propose radical reconfigurations of the tree of life. Most notably, evolutionary genomicists Maria Rivera and James Lake proposed the "ring of life" hypothesis. By analyzing the complete genomes of diverse microorganisms, they observed that the eukaryotic genome appears to be a profound genetic chimera, containing two distinct classes of genes. The "informational" genes, which are primarily responsible for transcription and translation, are most closely related to Archaea. Conversely, the "operational" genes, which are largely responsible for cellular metabolism, are most closely related to Bacteria. To account for this pervasive duality, Rivera and Lake argued that the eukaryotic lineage did not branch off independently, but rather emerged from a primordial fusion between an ancient bacterium and an ancient archaeon. In their view, the evolutionary relationship between the major forms of life is best represented not as a bifurcating tree, but as a continuous ring.

While Rivera and Lake’s genomic analysis is undeniably robust and elegantly accounts for the dual nature of eukaryotic genes, the structural mechanism they imply remains highly problematic. The literal fusion of two distinct prokaryotic cells into a single, functional eukaryotic ancestor requires an extraordinarily improbable sequence of cytological events. Specifically, it necessitates that one cell completely engulf another without digesting it, a process akin to modern phagocytosis. Yet, the complex cytoskeletal machinery and internal membrane systems required for phagocytosis are completely absent in modern prokaryotes and are generally considered a defining hallmark of the eukaryotic state—a state that, according to the hypothesis, had not yet evolved at the time of the fusion. Thus, the ring of life hypothesis, while offering a compelling genomic narrative, hinges on a cytological paradox. It successfully explains the *what* of the eukaryotic genome but stumbles significantly over the *how* of its physical inception, leaving researchers with a model that is genetically persuasive but mechanistically confounding.

The author's attitude toward Rivera and Lake’s "ring of life" hypothesis can best be described as which of the following?