1. Shared characteristics: This refers to the similarities an organism shares with others within a group. These similarities can be physical features (like number of legs, wing structure, etc.), genetic traits (like DNA sequences), or even behavioral patterns.

2. Evolutionary relationships: This refers to how closely related an organism is to other organisms based on their shared ancestry. This is determined by studying how organisms have changed over time, often by analyzing their evolutionary history through fossil records, DNA comparisons, or other methods.

Essentially, we classify organisms based on what they look like (shared characteristics) and how they're connected to other life forms (evolutionary relationships).