Directions: There are four black squares [<] in the passage, indicating where the following sentence could be added.
This definition is widely accepted by biologists and zoologists, but its application isn’t always simple.
Where would the sentence fit best?
Mark the square [<] to add the sentence to the passage.
Directions: Read the passage and answer the following question.
SALAMANDERS AND SPECIES NAMES
When reviewing the current journals of taxonomy, the science of organizing animals into neat little 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 the 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.
(A <) In biology, a species is typically defined as a group of animals that breed only with one another. (B <) Thus, any two animals that can breed belong to the same species, whereas animals that are unable to breed with one another are of a different species. (C <) 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. (D <)
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 salamanders have blotches that are more and more pronounced. Finally, by the time the southern tip of the valley is reached, the salamanders fully resemble the yellow and black spotted species. The salamanders in effect form an almost continuous ring around the outside of the Central Valley, and although the two distinct species at the “ends” of the ring do not interbreed, the salamanders can and do breed with “the intermediates” along the ring So although it is fairly clear that the salamanders at the ends of the ring are distinct species, what of the other salamanders found around the valley?
This situation presents quite a problem in classification. Most taxonomists have decided that the best solution is to put each of the intermediary salamanders into its own subspecies. However, this messy solution results in ten different species names for a salamander that is found only in the Central Valley. One can imagine how such a solution, applied to other species, could result in hundreds of thousands of subspecies for each species.
Further complicating the situation is the new evidence from genetic studies. It appears that the salamanders in Central Valley are all rather closely related, meaning that they all probably evolved from a common ancestor. A likely scenario is that the ancestral salamander species arrived at either the northern or southern tip of the valley and dispersed from there, with the offspring moving farther and farther down the eastern and western sides of the valley. In any case, the genetic evidence indicates a continuous gene flow along the Central Valley.
The case of the Central Valley salamander, sometimes called a ‘ring species,” is not unique. The salamander shows the difficulty of attempting to place animals into neat compartments although classification may be helpful to scientists and researchers, it is not a primary concern of the animals themselves—the salamander certainly doesn’t care what species it belongs to! Still despite the problems with the current taxonomic system it is admittedly useful. There is simply no other consistent way to label or classify the gradations found in nature, so the use of distinct species names will continue.