2017届广东省广州市天河区重点学校高考英语一轮复习检测：8（含答案）_高考复习指南

2017届广东省广州市天河区重点学校高考英语一轮复习检测：8（含答案）

　　A recent study of ancient and modern elephants has come up with the unexpected conclusion that the African elephant is divided into two distinct (不同的) species.

　　The discovery was made by researchers at York and Harvard Universities when they were examining the genetic relationship between the ancient woolly mammoth and mastodon to modern elephants—the Asian elephant, African forest elephant，and African savanna elephant.

　　Once they obtained DNA sequences (序列) from two fossils (化石), mammoths and mastodons, the team compared them with DNA from modern elephants.They found to their amazement that modern forest and savanna elephants are as distinct from each other as Asian elephants and mammoths.

　　The scientists used detailed genetic analysis to prove that the African savanna elephant and the African forest elephant have been distinct species for several million years.The divergence of the two species took place around the time of the divergence of Asian elephants and woolly mammoths.This result amazed all the scientists.

　　There has long been debate in the scientific community that the two might be separate species, but this is the most convincing scientific evidence so far that they are indeed different species.

　　Previously, many naturalists believed that African savanna elephants and African forest elephants were two populations of the same species, despite the elephants' significant size differences.The savanna elephant has an average shoulder height of 3.5 metres while the forest elephant has an average shoulder height of 2.5 metres.The savanna elephant weighs between six and seven tons, roughly double the weight of the forest elephant.But the fact that they look so different does not necessarily mean they are different species.However the proof lay in the analysis of the DNA.