Final answer:
Grouping organisms by similar structures and features can be problematic due to misleading appearances and the complexity of features. Misleading appearances can result in organisms that are distantly related appearing very similar, while those that are closely related may appear different. The complexity of features can make it challenging to differentiate between homologous structures and analogous structures.
Step-by-step explanation:
Grouping organisms by similar structures and features can be problematic for two main reasons. First, misleading appearances can lead to incorrect classification. Some organisms may look very similar but are actually distantly related, while others may look very different but are closely related. This can happen due to analogous structures or homoplasy, where similar characteristics arise from environmental constraints rather than evolutionary relationships. For example, insects, bats, and birds all have wings for flight, but their wing structures and embryonic origins are completely different.
Second, the complexity of features can make it difficult to determine shared evolutionary history. The more complex a feature is, the more likely any overlap is due to a common evolutionary past. However, it can be challenging to distinguish between homologous structures (which arise from shared evolutionary history) and analogous structures (which arise from convergent evolution). For instance, a hammer is a simple tool that can be independently invented by different people, but the complex structure of a car is highly unlikely to be independently invented in exactly the same way by different individuals.