The main reason is because they are heavy, and because they don't have to chase their food. They're not predators and their shells give them protection like running away gives protection to other herbivores.
Answer: The correct answer is silent mutation . In this type of mutation there is no change in the phenotype of the individual which means there occurs a mutation where two different amino acid codes for the same protein .There are sequences present in the body where a point mutation occurs but the protein formed is still the same .If you will see the genotype you can easily observe that the amino acid sequence is different but the protein formed is same. Example AAA codes for lysine and the amino acid lysine is formed by AAG .
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