Reading Practice Test 6: Science and Nature

Read the text below and answer questions 1-13.

The Silent Witnesses

When a body is discovered outdoors, one of the first questions investigators must answer is also one of the hardest: how long has it been there? Standard medical methods for estimating time of death, such as body temperature, become unreliable after roughly 48 hours. Beyond that window, an unlikely source of evidence takes over — insects.

Forensic entomologist Rosalind Okafor has spent the past decade studying how insects colonise remains in a predictable sequence. Blowflies are typically the first to arrive, often within minutes of death, drawn by odours imperceptible to humans. They lay eggs, which hatch into larvae that feed and develop through several distinct growth stages before pupating. Because each stage takes a fairly consistent amount of time at a given temperature, measuring which stage the larvae have reached allows an entomologist to estimate a minimum time since colonisation began.

Okafor's research goes further than simply timing blowfly development. She has catalogued the way different insect species arrive in overlapping 'waves' over weeks and months, each wave replacing the last as the remains change and as some insects finish feeding while others begin. A body found with only blowfly larvae present tells a very different story from one already colonised by beetles that typically arrive later, once decomposition has progressed further. By identifying which wave of species is present, and absent, investigators can narrow a time window far more precisely than by looking at a single species alone.

Temperature complicates the picture considerably. Insect development speeds up in warm conditions and slows dramatically in cold ones, so an estimate based on a fixed number of days would be seriously misleading without accounting for the actual temperatures the remains experienced. Okafor's team now cross-references local weather station data with development-rate tables built from laboratory-reared insects, adjusting their estimates accordingly. This step alone has, in casework she has reviewed, shifted some estimated time windows by more than a week compared to earlier, temperature-blind methods.

Forensic entomology is not without limitations. Indoor deaths, remains disturbed by scavenging animals, and cases where a body was moved after death all complicate the insect evidence, sometimes making it unreliable or impossible to interpret. Okafor is careful to note that entomological evidence works best as one part of a broader investigation, alongside traditional pathology, rather than as a stand-alone method. Even so, in cases beyond the reach of temperature-based estimates, insect evidence has repeatedly proven to be the most precise tool available.

Read the text below and answer questions 14-26.

Urban Foraging Wildlife

As cities have expanded into former farmland and forest, a surprising number of species have not simply retreated but adapted, taking up permanent residence within urban boundaries. Foxes navigate suburban streets at night, gulls nest on office rooftops far from any coastline, and raccoons in some North American cities now rarely venture beyond a few city blocks in their entire lives. Researchers studying this shift describe it not as animals tolerating cities, but as a genuine evolutionary response to a new kind of habitat.

One of the clearest examples is diet. Urban foxes studied in several European cities obtain a substantial portion of their calories from discarded food rather than hunted prey, and their skulls, measured across generations, show subtle changes consistent with a softer, less varied diet compared to rural populations. Behavioural changes have followed too: urban foxes in these studies are noticeably bolder around humans and quicker to investigate unfamiliar objects, a trait that would be dangerous in a rural setting full of natural predators but pays off when unfamiliar objects are just as likely to be a dropped meal as a threat.

Birds show a different but equally striking adaptation: many urban species have shifted the pitch and timing of their calls. Traffic and construction noise occupy lower frequencies, so several songbird species in noisy city centres now sing at a measurably higher pitch than their rural counterparts, allowing their calls to be heard above the background hum. Some species have also shifted to singing earlier, before the morning traffic builds, or later at night when the city is quieter.

Not every species adapts equally well, and researchers caution against treating urban wildlife success stories as evidence that cities are good for biodiversity generally. The species thriving in urban environments tend to be generalists — able to eat a wide range of food and tolerate disturbance — while specialist species, dependent on specific habitats or food sources, largely disappear from cities entirely. A city's wildlife population, though sometimes visible and abundant, typically represents a small subset of species compared to the surrounding countryside.

There are also genuine costs to this adaptation that researchers are only beginning to quantify. Urban foxes and raccoons show higher rates of certain diseases linked to dense population contact, and animals reliant on human food waste can suffer nutritional deficiencies despite appearing well-fed. Ecologists studying these populations generally agree that urban wildlife adaptation is a remarkable demonstration of evolutionary flexibility, but not a straightforward conservation success story.