Free IELTS Academic Reading Practice Test 7 & Answers

The domestic dog, Canis lupus familiaris, is the most widely abundant carnivore in the world. Despite the staggering variety of modern dog breeds—from the diminutive Chihuahua to the massive Great Dane—all dogs share a common ancestry with the gray wolf. The story of how a fearsome apex predator evolved into humanity’s most loyal companion is one of the most fascinating chapters in evolutionary history, though the exact timeline remains a subject of intense scientific debate.

For decades, archaeologists believed that dog domestication occurred roughly 10,000 to 14,000 years ago, coinciding with the advent of agriculture. The theory posited that wolves were drawn to the refuse dumps of early human farming settlements. The least aggressive wolves, those capable of tolerating human presence, scavenged for food and gradually evolved into domestic dogs. This is known as the “commensal scavenger hypothesis.” However, recent genetic sequencing of ancient canine remains has pushed the timeline much further back.

Modern genomic studies suggest that the divergence between dogs and wolves actually occurred between 20,000 and 40,000 years ago, deep in the Pleistocene epoch. This means dogs were domesticated by nomadic hunter-gatherers long before humans invented agriculture or established permanent settlements. During the harsh conditions of the Ice Age, humans and certain populations of wolves likely formed a mutually beneficial relationship. Wolves could assist humans in tracking and bringing down large prey, while humans could provide the wolves with a reliable share of the meat and warmth from their campfires.

Over generations, this symbiotic relationship fundamentally altered the wolves’ biology. Selecting for tameness inadvertently caused physical changes, a phenomenon known as “domestication syndrome.” The descendants of these wolves developed floppier ears, shorter snouts, smaller teeth, and piebald coat colors. More importantly, they developed unique socio-cognitive skills. Unlike wolves, modern domestic dogs can understand human pointing gestures and frequently make eye contact with humans when faced with an unsolvable problem, actively seeking our help.

A. Water covers approximately 71% of the Earth’s surface, earning it the moniker “The Blue Planet.” However, less than 3% of that water is fresh, and the vast majority of it is locked away in glaciers and ice caps. As the global population continues to explode and climate change disrupts historical rainfall patterns, severe freshwater shortages are threatening regions across the globe. To combat this looming crisis, many arid nations are turning to the ocean, heavily investing in desalination technology.

B. Desalination is the process of removing dissolved salts and minerals from seawater to make it suitable for human consumption or irrigation. There are two primary methods used today: thermal desalination and reverse osmosis (RO). Thermal desalination, the older of the two, involves boiling seawater and collecting the purified vapor as it condenses, leaving the salt behind. While effective, this method requires staggering amounts of thermal energy, making it economically unfeasible for most nations outside the energy-rich Middle East.

C. Consequently, reverse osmosis has become the global standard. In an RO plant, high-pressure pumps force seawater through a series of semi-permeable polymer membranes. The microscopic pores in these membranes are large enough to allow water molecules to pass through but small enough to block salt ions and other impurities. Because it relies on pressure rather than heat, reverse osmosis uses significantly less energy than thermal plants, though it remains much more energy-intensive than treating traditional freshwater sources like rivers or aquifers.

D. Despite its life-saving potential, the desalination industry faces intense criticism regarding its environmental impact. The most pressing issue is the disposal of brine—the highly concentrated, ultra-salty wastewater left over after the freshwater is extracted. When this dense, toxic brine is pumped back into the ocean, it sinks to the seafloor, suffocating marine ecosystems, particularly sensitive coral reefs and seagrass meadows. Furthermore, the intake pipes that suck in seawater frequently trap and kill millions of fish, larvae, and plankton.

E. To make desalination a truly sustainable solution, engineers must address these ecological and energetic shortcomings. Current research is focusing on powering RO plants with renewable solar energy rather than fossil fuels. Additionally, innovators are exploring ways to “mine” the leftover brine, extracting valuable commercial minerals like lithium, magnesium, and calcium. If successful, this could transform a toxic waste product into a profitable resource, offsetting the high costs of the desalination process.

In 1964, a young woman named Kitty Genovese was tragically murdered outside her apartment building in Queens, New York. Initial media reports sensationally claimed that 38 witnesses saw or heard the attack, yet not a single person intervened or called the police until it was too late. While later historical investigations proved these initial newspaper reports were heavily exaggerated, the narrative of the apathetic urban public sparked a frenzy of psychological research. The resulting studies led to the identification of a profound social phenomenon known as the “Bystander Effect.”

The Bystander Effect posits that the probability of a person offering help to a victim decreases as the number of observers increases. Social psychologists John Darley and Bibb Latané, who pioneered research in this field, demonstrated that this inaction is rarely born out of malice or genuine apathy. Instead, it is driven by powerful, unconscious psychological mechanisms. The most prominent of these is the “diffusion of responsibility.” When a person is the sole witness to an emergency, 100% of the responsibility to act rests on their shoulders. However, in a crowd, that psychological burden is divided among everyone present. Individuals unconsciously assume that someone else—perhaps someone more qualified, like a doctor or an off-duty police officer—will take action.

Another major factor contributing to bystander inaction is “pluralistic ignorance.” Emergencies are inherently ambiguous and highly stressful situations. When faced with uncertainty, humans naturally look to the behavior of those around them for cues on how to act. If an individual sees a person slumped on a park bench, they might wonder if the person is having a heart attack or simply sleeping. If the individual looks around and sees that no one else seems panicked or is rushing to help, they will likely conclude that the situation is not a real emergency. Because everyone in the crowd is looking at each other for cues, and everyone is trying to appear calm, a collective illusion is created that no action is necessary.

Understanding the Bystander Effect is crucial for overcoming it. Psychologists advise that if you are ever the victim of an emergency in a crowded place, you should not yell a general cry for “Help!” Doing so allows the diffusion of responsibility to take hold. Instead, you should point directly at a specific individual and give them a direct command, such as, “You in the red shirt, call an ambulance!” By singling out an individual, you completely shatter the diffusion of responsibility, forcing that specific person to act.