Questions 53 - 55 refer to the article below.
Era of ’Biological Annihilation’ Is Underway, Scientists Warn
…Thousands of animal species are in precipitous decline, a sign that an irreversible era of mass extinction is underway, new research finds.
Dr. Ceballos, a researcher at the Universidad Nacional Autónoma de México, emphasized that he and his co-authors, Paul R. Ehrlich and Rodolfo Dirzo, both professors at Stanford University,… are using scientific data to back up their assertions that significant population decline and possible mass extinction of species all over the world may be imminent, and that both have been underestimated by many other scientists.
The study’s authors looked at reductions in a species’ range— a result of factors like habitat degradation, pollution and climate change, among others— and extrapolated from that how many populations have been lost or are in decline … .
They found that about 30 percent of all land vertebrates… are experiencing declines and local population losses. In most parts of the world, mammal populations are losing 70 percent of their members because of habitat loss.…
Dr. Jonathan Losos, a biology professor at Harvard,… noted that giving precise estimates of wildlife populations was difficult, in part because scientists do not always agree on what defines a population… .
The authors of the paper suggest that previous estimates of global extinction rates have been too low, in part because scientists have been too focused on complete extinction of a species… .
Scientists estimate that 200 species have gone extinct in the past 100 years; the “normal” extinction rate over the past two million years has been that two species go extinct every 100 years because of evolutionary and other factors.
Dr. Ehrlich, who wrote “The Population Bomb,” a book that predicted the imminent collapse of humanity because of overpopulation, and Dr. Ceballos said that habitat destruction … and pollution were the primary culprits, but that climate change exacerbates both problems. Accelerating deforestation and rising carbon pollution are likely to make climate change worse, which could have disastrous consequences for the ability of many species to survive on earth.
Dr. Ceballos struck a slightly more hopeful tone, adding that some species have been able to rebound when some of these pressures are taken away. …
Based on the passage, which of the following describes the author’s perspective on why historical extinction rates were lower than present-day rates?