Anatomical and physiological character because these character describe the evolutionary relationship between organisms. Due to changing of environmental condition or different geographical condition the individuals of same species may adapted differently or got different external feature due to natural selection but their anatomy (internal structure) should be same as their ancestor. For example homology and analogy organs play major role in finding the evolutionary relationship between organisms and they define by study of anatomy of organisms.

An important criterion for modern day classification is anatomical and physiological traits.

Modern day classification is based on a variety of criteria that help scientists organize and categorize organisms. One of the most important criteria for classification is the examination of anatomical and physiological traits. This involves studying the physical structures and functions of organisms in order to determine their evolutionary relationships and place them into appropriate taxonomic groups.

Importance of anatomical traits:

Anatomical traits refer to the physical characteristics of organisms, including their external and internal structures. These traits can provide valuable information about an organism's evolutionary history and relationships with other species. By comparing the anatomical features of different organisms, scientists can identify similarities and differences that indicate their relatedness.

Importance of physiological traits:

Physiological traits, on the other hand, are related to the functions and processes that occur within an organism's body. These traits include things like metabolism, reproduction, respiration, and circulation. By studying the physiological traits of different organisms, scientists can gain insights into their evolutionary adaptations and how they have adapted to their environments.

Why anatomical and physiological traits are important for classification:

1. Evolutionary relationships: Anatomical and physiological traits can provide valuable information about an organism's evolutionary history and relationships with other species. Similarities in these traits often indicate a close evolutionary relationship, while differences suggest a more distant relationship.

2. Diagnostic features: Anatomical and physiological traits can act as diagnostic features for identifying and classifying organisms. For example, the presence of certain anatomical structures or physiological processes can help distinguish between different groups of organisms.

3. Functional adaptations: Anatomical and physiological traits can also reveal how organisms have adapted to their environments. For example, the presence of certain physiological adaptations like specialized respiratory systems or reproductive strategies can indicate how an organism has evolved to survive and reproduce in specific habitats.

4. Taxonomic classification: By examining anatomical and physiological traits, scientists can assign organisms to specific taxonomic groups, such as phylum, class, or order. This helps in organizing and categorizing the vast diversity of life on Earth.

In conclusion, anatomical and physiological traits are crucial criteria for modern day classification. They provide insights into an organism's evolutionary relationships, help identify diagnostic features, reveal functional adaptations, and aid in taxonomic classification. By studying these traits, scientists can gain a deeper understanding of the natural world and how different species are interconnected.