Answer:
Classification systems keep changing because our knowledge about living organisms is continuously increasing. As new information and better techniques become available, earlier systems of classification are modified or replaced.
Reasons for frequent changes in classification systems:
• Discovery of new organisms with unique characteristics
• Better understanding of structural, physiological and developmental features
• Advances in microscopy and molecular biology
• Use of biochemical and genetic data in classification
• Improved understanding of evolutionary relationships among organisms
Conclusion:
Thus, classification systems change from time to time to make them more natural, scientific and reflective of true evolutionary relationships.