tailieunhanh - Cracking the Toefl IBT 2009 edition part 24

Tham khảo tài liệu 'cracking the toefl ibt 2009 edition part 24', ngoại ngữ, toefl - ielts - toeic phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | READING DRILL 3 Salamanders and Species Names When reviewing the current journals of taxonomy the science of organizing animals into neat classifications it is important to remember that names are a human convenience. Nature is not concerned with putting her creations into simple and objective categories. The classifications that we now have are the result of scientists need to put some sort of order into what is a very chaotic situation. And although taxonomists have the best intentions when naming and classifying new or existing species there are many occasions when naming a species causes quite a bit of confusion. An excellent example of the problem with naming species is the case of Ensatina. a genus of salamander found in the Central Valley area of California. Central Valley is about 40 miles wide and although salamanders do not live in the valley itself they are found in the forests and mountains that ring the valley. At the southern tip of the valley live two distinct types of salamander one salamander is characterized by its yellow and black spots whereas the other is light brown in color and has no spots. In biology a species is typically defined as a group of animals that breed only with one another. Thus any two animals that can breed belong to the same species whereas animals that are unable to breed with each other are of a different species. The two Central Valley salamanders do not interbreed which would seem to make it pretty clear that the salamanders should be classified as different species. But there is one interesting problem with these salamanders. A number of other salamanders inhabit the ring surrounding Central Valley. Moving north along the eastern side of the valley the salamanders have fewer and fewer blotches. At the northern end of the valley the salamanders appear to be a mixture of the two species these salamanders are mostly brown but they still have visible blotches. Now moving south along the western end of the valley the .