PASSAGE 2 – Questions 11–20

Based on fossils retrieved from South Africa’s Rising Star cave, two research teams reconstructed the movement habits of Homo naledi — a mysterious human ancestor. With funding from National Geographic, one team examined 107 foot bones, while the other studied 26 bones from a nearly complete right hand.

In most respects, the H. naledi foot looks surprisingly similar to that of modern humans. Its ankle joint, parallel big toe, and wide heel bone belong to a striding biped fully adapted to walking upright. However, its lower arch and curved toe bones are more ape-like. The hand, with its curved fingers, indicates that H. naledi were strong climbers—yet the long, robust thumb and shock-absorbing wrist suggest potential tool use (though no tools have yet been found). This combination of traits had never been clearly observed in the genus Homo, to which modern humans belong.

“H. naledi had a unique form of movement for a member of the genus Homo,” says study author William Harcourt-Smith of CUNY’s Lehman College. When, in the course of human evolution, did our ancestors climb down from the trees and begin striding across the land? It is difficult to determine. Lucy and other early australopithecines walked upright about four million years ago, yet they were still climbers and may have used simple stone tools. Evidence for tree-climbing among the Homo lineage is rare. Scientists suspect that Homo habilis, the “handy man,” retained climbing abilities around two million years ago, though this view relies on limited fossils. Now, the hands of H. naledi show that despite its modern feet and walking style, the species also retained ape-like climbing traits.

Throughout most of human evolution, our ancestors combined walking and climbing skills, which helped them adapt to changing environments, says Stony Brook University’s Bill Jungers. H. naledi was no exception. Because the fossils from Rising Star have yet to be dated, its exact place in human evolution remains uncertain. Based on morphology alone, it may belong near the base of the Homo genus. If H. naledi is as old as 2 to 2.5 million years, it would suggest that hand features enabling tool use appeared earlier than previously believed, notes study author Tracy Kivell of the University of Kent. Conversely, if H. naledi is relatively young—perhaps 100,000 years old—it would mean that climbing traits like curved fingers were retained (or re-evolved) in a hominin that coexisted with modern humans. “Both scenarios are very interesting,” Kivell concludes.

11. What is a *Homo naledi*?

PASSAGE 3 – Questions 21–30

The most essential requirement for life is the presence of liquid water—not only as part of the chemical reactions of life but also as a medium for transporting nutrients and wastes within organisms.

The water requirement automatically rules out many worlds in our solar system. The Moon is airless, and although some data suggest ice frozen in its polar soil, it has never had liquid water on its surface. Mercury is also airless and cannot retain liquid water for long. Venus contains traces of water vapor in its atmosphere, but it is far too hot for liquid water to exist.

The inner solar system appears too hot, while the outer solar system is too cold. The Jovian planets have deep atmospheres, and at certain levels, the temperature may allow water to condense into droplets. Yet it is unlikely that life could originate there: these planets lack solid surfaces where oceans could nurture life, and their powerful atmospheric currents move gas and water between regions that are either too hot or too cold for survival.

Some of the Jovian satellites might possess suitable conditions for life. Jupiter’s moon Europa appears to have a liquid-water ocean beneath its icy crust. However, Europa may not be a promising site because conditions might not have remained stable for the billions of years needed for life to evolve beyond microscopic forms. If Jupiter’s moons have altered their orbits through gravitational interactions, Europa may have been frozen solid during certain periods.

Saturn’s moon Titan may contain oceans of liquid methane and ethane on its surface. The potential chemistry of life in such an environment is unknown, but life there seems unlikely due to the extreme cold. Titan’s surface temperature is around −173°C (−290°F), where chemical reactions occur very slowly or not at all. As a result, the chemical evolution necessary for life may never have taken place on Titan.

Mars remains the most likely place for life within our solar system, though the evidence is inconclusive. Meteorite ALH84001, discovered in Antarctica in 1984, is believed to have originated from Mars after being ejected into space by a massive impact. The meteorite gained attention in 1996 when scientists announced that it contained chemical and structural traces of ancient life on Mars.

While the announcement generated excitement, many scientists remained skeptical and began re-examining the data. In many cases, the results did not confirm the conclusion that life once existed on Mars. Some contamination from Earth’s water was detected, and certain chemicals within the meteorite may have originated through non-biological processes. The microscopic features resembling fossil bacteria may instead be mineral formations within the rock.

Consequently, the ongoing search for extraterrestrial life now extends beyond our solar system, to distant planetary systems across the galaxy.

21. The word “**automatically**” in the passage is closest in meaning to…

PASSAGE 4 – Questions 31–40

Taken together, income, occupation, and education are reliable measures of people’s social standing. Using a layered model of stratification, most sociologists describe the class system in the United States as: upper, upper middle, middle, lower middle, and lower class. These classes are arranged along a continuum, with those possessing the most money, education, and prestige at the top and those with the least at the bottom.

In the United States, the upper class owns a major share of both corporate and personal wealth. It includes families with inherited fortunes as well as those who have recently become rich. Although only a small percentage of the population belongs to this class, they control vast amounts of wealth and power and exercise considerable influence across society.

Despite the common myth of equal opportunity, the best predictor of future wealth remains the family into which one is born. Each year, the business magazine Forbes publishes a list of the 400 wealthiest individuals and families in the country, and most of that wealth is inherited. Those with newly acquired fortunes are known as the nouveau riche. Luxury cars, expensive real estate, and exclusive vacations often characterize the lifestyle of the newly rich.

The middle class includes individuals with high incomes and significant social prestige, such as professionals and business executives. Estimating the size of this group is difficult because the boundaries between upper, upper-middle, and middle classes are blurred. The upper-middle class is often thought of as “middle class” because its lifestyle represents the standard many aspire to, though it remains beyond the reach of most Americans.

Defining the middle class is complex, as it involves more than economic status. Many Americans identify as middle class even though their lifestyles and resources vary widely. The belief that the United States is an open-class society leads many to assume that most people enjoy a middle-class lifestyle.

The lower middle class includes skilled tradespeople and lower-income clerical or service workers, such as secretaries, hair stylists, food servers, police officers, and firefighters. While many of them consider themselves middle class, their position in the hierarchy is lower. The term “lower” in this classification simply indicates relative standing but often carries a negative connotation for those within the group.

The lower class consists mainly of the displaced and the poor. Members of this class generally have limited education and work in low-wage or unstable jobs. Around six percent of all working people live below the poverty line. Within this category, the “underclass” refers to those who are permanently unemployed or without stable means of economic support. Excluded from the mainstream economy, members of the underclass may depend on public assistance or turn to illegal activities for survival.

31. The word “**those**” in the passage refers to…