The extinction of the Tasmanian tiger, or thylacine, on the Australian mainland has long been attributed to human activity, particularly hunting by indigenous populations and later European settlers. However, recent archaeological and ecological evidence suggests that climate change was the primary driver of its disappearance from the mainland around 3,000 years ago. First, fossil records indicate a sharp decline in thylacine populations during a period of significant aridification, when Australia's interior became increasingly dry and hot. This climatic shift reduced the open woodlands and grasslands that supported the thylacine's prey, such as small kangaroos and wallabies, leading to food scarcity. Second, DNA analysis of ancient thylacine remains shows a loss of genetic diversity prior to extinction, consistent with a population bottleneck caused by environmental stress rather than sudden human hunting pressure, which would have left different genetic signatures. Third, ethnographic records from Aboriginal oral traditions describe the thylacine as a rare and elusive creature even before European contact, suggesting that its numbers were already low due to natural causes. In contrast, human hunting, while present, was likely sporadic and focused on other species, as thylacine bones are rarely found in archaeological middens compared to those of other animals.
🎧 听力讲座
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The lecture challenges the reading's claim that climate change was the main cause of the thylacine's mainland extinction. While the professor acknowledges that aridification occurred, she argues that human activity, specifically the introduction of the dingo, was the decisive factor. First, the dingo, which arrived in Australia around 4,000 years ago, was a direct competitor and predator of the thylacine. Dingoes are more adaptable and hunt in packs, outcompeting the solitary thylacine for the same prey. This competition, not climate, would have caused the food scarcity observed in the fossil record. Second, the genetic diversity loss cited in the reading can be explained by human actions. Dingoes may have introduced diseases to which thylacines had no immunity, causing rapid population crashes and genetic bottlenecks. Alternatively, targeted hunting by humans, who viewed thylacines as a threat to livestock, could have had the same effect. Third, the reading's reliance on Aboriginal oral traditions is problematic, as these stories may reflect cultural perceptions rather than actual population numbers. Moreover, archaeological evidence shows that thylacine remains become increasingly rare precisely after the dingo's arrival, while climate remained stable during that interval. Thus, the lecture concludes that the dingo's introduction, facilitated by human migration, was the primary cause of the thylacine's mainland extinction.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
