Kaplan Nursing Entrance Practice Exam

What is a defining characteristic of mammals?

1. Feathers

2. Hair

3. Scales

4. Shells

The correct answer is: Hair

Mammals are characterized by the presence of hair or fur at some stage of their life cycle. This defining characteristic allows mammals to regulate their body temperature, providing insulation to maintain warmth in a variety of environments. Hair also plays roles in sensory perception and camouflage. In contrast, feathers are unique to birds, scales are found on reptiles and fish, and shells are typically associated with certain invertebrates, such as mollusks. The presence of hair is a key evolutionary trait that differentiates mammals from other animal groups, making it an essential aspect of their biology and adaptation. This defining feature is integral to the classification and identification of mammals in the animal kingdom.