About 6,000 years ago, people in Britain stopped eating fish and shifted to cattle, sheep, pigs and goats in an abrupt and mysterious transformation（変化） that may offer new insights into the complex reasons why ancient peoples periodically changed their way of life. The dietary switch occurred as part of the Neolithic Revolution, a set of radical pre-Bronze Age changes that included the introduction of domesticated plants and animals “But why did people suddenly stop doing the things they did before?” asked archaeologist(考古学者) Michael Richards. “In most Old World areas, it was much more gradual. Why not in Britain? This is the big question.” Changes in diet usually signal major upheavals in ancient societies. Scholars closely track the pace of these shifts, looking for clues in trying to understand why civilizations rise and fall or change when and where they do.
why civilizations rise and fall or change ( when and where they do.) s v doは下線部の代動詞
構文としては、（ ）内がrise and fall or change を修飾しています。 構文を尊重して、かつ日本語の語順に直して訳すと以下になります。
Richards, reporting with two colleagues in the Nature, analyzed bones from 183 ancient Britons. They found people who died more than 6,000 years ago lived on fish, while those who died after that were all meat-eaters. “It spread like wildfire, probably because it was much more secure than when you're at the mercy of wild food.” But he noted that ancient Britons had no apparent reason to abandon a sophisticated(洗練された) culture that used hooks, lines, nets, weirs and fish traps. Also, he noted that the ancient Danes similarly underwent a shift from fish to meat at the same time as the Britons. “But even though they were on the European mainland, they had ignored similar changes elsewhere on the continent for 1,000 years.” The shift to animal husbandry in Britain is markedly different from the gradual pace of agricultural expansion from the Middle East, where the Neolithic Revolution began 10,500 years ago with the domestication of grains and animals. “It spread gradually across Europe and Asia”, said archaeological chemist Patrick McGovern. They domesticate one thing, then go on to another. The attractions of agriculture are obvious in the archaeological record. A population with a stable food supply multiplies rapidly and organizes in ways that encourage collective action and innovation―the beginnings of civilization. Archaeologist Stan Abler has studied two contemporary Native American communities, Menoken and Jones Village, about 100 km apart in North and South Dakota. Both are Neolithic-style sites dated between A.D. 1100 and 1200. “Menoken, which had no agriculture, has little earth-covered houses, and it's scaled way down,” Abler said. “Everything about Jones Village, where they grew crops, is magnitudes bigger. It has grain-storage facilities and more elaborate and bigger houses for bigger families.” But agriculture has its disadvantages. Several major scourges sprang from domesticated animals, including smallpox (cattle), anthrax (sheep) and flu (pigs). And reliance on single crops does not necessarily promote good health. “There's a tradeoff,” Richards said. “With domesticated plants and animals, we can produce so much food that we multiply much more quickly.” Neolithic sites hold a lot more human remains than older sites, he added, “but the bones look a lot less healthy.”