Final answer:
The shaft of the hair is considered class evidence because it has certain properties like hair color and texture that can be used to group individuals rather than pinpoint a unique source.
Step-by-step explanation:
The shaft of the hair is considered class evidence in a trial largely because it can be used to include or exclude a group of people but cannot be associated with a single source with high certainty. This classification is due to aspects like color properties and texture, which can be common to several individuals.
While DNA can provide a link to a unique individual, DNA is not typically obtained from the hair shaft itself but rather from the root; hence, the hair shaft is considered class evidence not individual evidence.