Which choice best describes the function of the fourth paragraph (beginning "The significance of this finding") in the passage as a whole?

Archaeologists studying ancient diets have traditionally relied on what survives in the ground: seeds, animal bones, cooking vessels, occasionally a preserved grain of pollen. These sources are genuinely useful, but they share a common limitation. They tend to preserve foods that leave something durable behind, and they say little or nothing about foods that were fully consumed, thoroughly digested, or simply too perishable to survive centuries in the soil. A diet reconstructed only from what happens to endure physically is, by definition, a partial diet.

An unexpected source has begun filling in some of these gaps: the hardened plaque, called dental calculus, that forms on teeth during a person's life and, if never removed, mineralizes and remains fixed to the tooth long after the rest of the body has decayed. Dental calculus is not itself food. It forms from minerals in saliva combining with the bacterial film that naturally coats teeth. But as it forms, it traps and seals in tiny fragments of whatever passed through the mouth while it was accumulating, preserving them in a mineral shell far more durable than the food itself ever was.

Researchers analyzing calculus from 100 archaeological samples, spanning roughly two and a half thousand years of English history, applied a technique capable of identifying preserved proteins at the molecular level. The results, summarized in Table 1, included direct evidence of dairy consumption, specifically a milk protein detectable in a meaningful share of the samples tested, alongside proteins from plant foods including grains and legumes. None of this dietary evidence would have been visible under an ordinary microscope, and much of it would have left no trace at all in the conventional archaeological record of bones and pottery.

The significance of this finding extends beyond simply adding dairy to a list of foods a particular population ate. Milk consumption is a detail that matters for a much larger question in human history: when and where populations began regularly consuming dairy, a practice connected to genetic changes that allow some adult humans, but not others, to digest milk sugar efficiently. Direct molecular evidence from calculus offers something the indirect evidence archaeologists have traditionally relied on cannot: dietary information tied to specific individuals in a known place and time, rather than population-level inference built from indirect proxies alone.

None of this makes older methods obsolete. Bones, seeds, and pottery still tell archaeologists things calculus cannot, including where and how food was prepared, stored, or exchanged. What calculus adds is a second, largely independent line of evidence, drawn from an entirely different kind of physical record, capable of confirming or complicating a picture built from more traditional sources.

Table 1. Selected results from the proteomic study described in the passage

| Measure | Archaeological samples | Modern comparison samples |
|---|---|---|
| Samples analyzed | 100 | 14 |
| Samples with identifiable dietary protein evidence | 26 | 4 |
| Most frequently detected dietary protein | Milk protein (beta-lactoglobulin) | Milk protein (beta-lactoglobulin) |
| Examples of detected plant-based proteins | Oats, peas, cruciferous vegetables | Not specified in the passage |