What criteria is primarily used in the classification of organisms?

The classification of organisms is primarily based on morphological features, which refer to the structural characteristics and physical forms of organisms. Morphology includes aspects such as shape, size, color, and structural arrangements of various parts of an organism. This approach is fundamental because it provides a visible and measurable basis for categorizing species and understanding their relationships.

Morphological classification helps in establishing evolutionary connections and can be done by examining various traits, such as anatomical structures—bones, leaves, or flowers—and identifying similarities and differences that reflect shared ancestry or adaptation to specific environments.

While behavioral traits and geographical location can offer additional context for understanding species' ecology and evolution, they do not serve as the primary basis for the initial classification of organisms. Behavioral traits are often more variable and can change within species due to environmental pressures. Geographical location may indicate how species are distributed or how they adapt to different environments, but morphology remains the more consistent criterion used in taxonomy to categorize organisms into various groups.