Question

The following passages were adapted from articles discussing evolutionary biology.

Passage A
Horizontal gene transfer (HGT)—the sharing of genetic material between organisms that are not in a parent-offspring relationship—has fundamentally dismantled the classic Darwinian conception of the "tree of life." For over a century, evolutionary biologists mapped species divergence using a branching tree model, assuming that genetic traits were exclusively inherited vertically from ancestors to descendants. However, modern genomic sequencing has definitively revealed that among prokaryotes, HGT is not merely an occasional anomaly, but a pervasive, dominant mechanism driving adaptation and speciation. Entire genetic pathways coding for critical functions, such as antibiotic resistance or complex metabolic capabilities, can be swiftly exchanged across entirely diverse taxonomic lineages.

Consequently, attempting to trace clear, bifurcating lineages for these organisms is scientifically futile. When genes are routinely swapped across branches, determining a single universal common ancestor becomes computationally and logically impossible. Instead of a tree with distinct, diverging branches, evolutionary history, at least at the foundational microbial level, is much more accurately represented as a tangled web or a dense, interconnected thicket. In this model, genetic material flows laterally across boundaries almost as freely as it is handed down vertically. This paradigm shift requires researchers to abandon the restrictive framework of the evolutionary tree, as it obscures the dynamic, fluid nature of microbial evolution and fails to capture the true complexity of how life has diversified on Earth.

Passage B
The discovery of widespread horizontal gene transfer (HGT) among bacteria and archaea has rightfully prompted evolutionary biologists to refine their models of genetic inheritance. It is undeniably true that lateral gene flow complicates the neat, bifurcating branches of the traditional evolutionary tree. Yet, recent calls by some microbiologists to entirely abandon the tree of life metaphor in favor of a "web" or "net" are premature, disproportionate, and ultimately unhelpful for the broader field of biology.

While HGT is undeniably a primary driver of prokaryotic evolution and has shaped the genomes of many single-celled organisms, its role in the evolution of complex eukaryotes—such as plants, animals, and fungi—remains relatively marginal. For these macroscopic organisms, which constitute the vast majority of described species, vertical descent through sexual reproduction continues to be the overwhelming mechanism of genetic transmission. The traditional tree model remains a robust, mathematically sound, and highly accurate framework for mapping the evolutionary history and phylogenetic relationships of eukaryotic life. Therefore, rather than discarding the tree metaphor entirely due to the complexities of the microbial world, biologists should recognize it as a foundational model that merely requires specific, localized modifications. We are looking at a tree with some tangled roots and occasional cross-branch grafting, but the trunk and the canopy remain very much intact, governed by the classic principles of vertical descent.

Which one of the following most accurately describes the primary purpose shared by both passages?