Final answer:
The evolutionary relationships between certain species cannot be explained thoroughly due to the historical focus on shared characteristics, new discoveries in genetic analysis, and the subjective nature of taxonomy.
Step-by-step explanation:
The evolutionary relationships between certain species cannot be explained thoroughly due to several factors. One reason is that the classification of organisms historically focused on grouping them based on shared characteristics, which may not necessarily reflect their evolutionary relationships. Additionally, new discoveries and advancements in genetic analysis often lead to changes and updates in phylogenetic classifications. Furthermore, the task of organizing the evolutionary relationships of all life on Earth is challenging and subjective, as different taxonomists may decide on different connections between organisms.