Step 1: Understanding the Concept:
The question asks to identify an "acquired" trait among the given options used for classifying tribes. An acquired trait is one that is learned or developed during one's lifetime, as opposed to an innate or inherited trait.
Step 2: Detailed Explanation:
Let's analyze the options:
(A) language: Language is learned from the community and family. It is not biologically inherited. Therefore, it is a classic example of an acquired cultural trait.
(B) livelihood: While the methods of livelihood (e.g., hunting, agriculture) are learned, they are often heavily determined by the environment (habitat). It is an acquired trait, but language is a more fundamental cultural marker.
(C) racial features: These refer to physical characteristics like skin color, hair type, and facial structure. These are genetically determined and inherited, making them innate, not acquired.
(D) habitat: This refers to the geographical area where a tribe lives. It is an external condition or environment, not a trait of the people themselves, acquired or otherwise.
In the classification of Indian tribes, both permanent (racial) and acquired (language, livelihood) traits are used. However, among the choices provided, racial features are innate, and habitat is an external factor. Language is the clearest example of a significant cultural trait that is acquired and used for classification (e.g., classifying tribes into linguistic families like Austro-Asiatic, Tibeto-Burman, Dravidian).
Step 3: Final Answer:
Language is an acquired trait used to classify tribal populations.