What information can be determined by examining the size and shape of a hair medulla?

The examination of the size and shape of a hair medulla can provide valuable information regarding the species or racial origin of the hair sample. The medulla is the central core of the hair, and its characteristics can vary significantly among different species and even among individuals within a species. For instance, human hair typically has a medulla that is either absent or very thin, while many animal hairs have a more prominent medulla, which can often be hollow or varied in structure.

This morphological feature can help forensic scientists and researchers distinguish between human hair and other animal hairs, as well as potentially identify racial or ethnic backgrounds based on the specific traits of the medulla. Therefore, analyzing the medulla's size and shape is a practical method for determining the origin of hair samples in forensic investigations, making this the most relevant and accurate choice among the options provided.