1 . Experiments conducted by researchers from the University of Chicago have finally unveiled the mechanism behind the elephant’s ability to avoid cancer, helping us better understand a riddle known as Peto’s paradox. It goes like this: the more cells an animal has, the more opportunities it should have to develop cancer. Within any given species, this appears to ring true. Larger species of dog seem to have a greater chance to cancer than smaller ones, for example. But when comparing animals of different species, the concept falls down. There is zero relation between the size of an animal’s body or its relative lifespan and the chance of cancer popping up among all those cells. Named after epidemiologist(流行病学家) Richard Peto, the paradox has confused biologists for decades. Clearly growing to be bigger has meant finding more efficient ways to make sure cancer didn’t also take advantage.
Elephants are a textbook example. In 2015, researchers estimated their cancer rate stood at just under 5 percent, compared with the 11 to 25 percent for the relatively small human body. That study also found a potential clue to the elephant’s anti-cancer superpower in the form of a gene called TP53. Like most anti-cancer genes, it makes a product that detects DNA damage and tells the cell to either fix it or close shop. Most mammals have two copies of the gene. Elephants have twenty, suggesting they’re well prepared to spot the threat of cancer early and act on it at a moment’s notice.
Geneticist Vincent Lynch and his team took a special approach by taking tissue samples from elephants and their smaller relatives such as the manatee(海牛) and the kitten-sized hyrax(蹄兔), and attacking them with carcinogens. “The elephant cells just died; they were entirely intolerant of DNA damage in a way their relatives’ cells were not,” says Lynch. “Because the elephant cells died as soon as their DNA was damaged, there was no risk of them ever becoming cancerous.”
1. What can we learn from paragraph 1?
| A．Elephants never develop cancer. |
| B．More cells means more chances of cancer. |
| C．The paradox contains contradictory ideas. |
| D．Animals avoid cancer in different ways. |
2. What might contribute to elephant’s ability to avoid cancer?
| A．The size. | B．The lifespan. | C．The gene. | D．The number of cells. |
3. What does the underlined word “carcinogens” mean in paragraph 3?
| A．Tissue sample from relatives. | B．Substances causing cancer. |
| C．Cells with damaged DNA. | D．Viruses from other mammals. |
4. What can we infer about elephants’ smaller relatives in the research?
| A．They have a lower risk of getting cancer. |
| B．They have the same DNA structure as elephants. |
| C．Their DNA was attacked but not damaged. |
| D．Some of their cells survived the attack. |
