3. A species of rats live in a certain type of tree with the branches evenly spaced. Smaller rats could not reach from branch to branch and larger rats would break the branches and fall. Soon, all rats were just the right size for the tree branches. Analyze the given example and evaluate how variation, adaptation and natural selection are major components of evolution.

Different body size of the rat population serves as variations. The smaller and larger rats cannot reach the branches but the rats with average body size are better adapted to reach the tree branches. The change in body size (average) is a result of random mutation. Due to their better fitness to the given habitat, their population size increases resulting in an increased number of rats with average body size in the population.  

Explanation:  

Evolution represents the accumulation of variations in the population of organisms. These variations are imparted by evolutionary agents. Mutation, genetic recombination, gene flow serve to add new genetic variations in the populations. These variations are the raw materials on which evolutionary forces act to bring about changes in the populations.  

Natural selection serves to drive the process of evolution. It requires the presence of genetic variations in the population. The organisms with the genetic traits that allow them to survive well in the given conditions are favoured by natural selection. This results in an increased frequency of the beneficial genetic trait in the population with generations.

In the given example, the rat population exhibits genetic variation for body size. The population has rats of smaller and larger body size. The smaller rats find it difficult to reach the branches of trees. On the other hand, the larger rats can reach the branches but fall off due to breaking of the branches. Random mutations give rise to rats of average size that can reach the branches without breaking them apart. They are adapted to the pattern of the trees grown in the habitat. They survive well and reproduce more to leave more progeny. With time, the number of rats with average body size is increased in the population and the population is said to be adapted to reach the tree branches.  

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.

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