Which of the following is not an example of developmental changes under 'disappearance of old features'?

Question

Accepted Answer

The correct option is 4: Primary sex characteristics.

In the study of human development, changes are often categorized into two types: those involving the acquisition of new features (like learning to walk or developing permanent teeth) and those involving the disappearance or replacement of old features. Primary sex characteristics (the internal and external reproductive organs) are present from birth, although they mature during puberty. Their *appearance* or *existence* is not a feature that disappears during normal development; rather, they *grow* and *mature*. Therefore, their development falls under the category of 'acquisition or maturation of new or existing features,' not 'disappearance of old features.'

The incorrect option is 1: Thymus Gland. The thymus gland is a feature that diminishes significantly (atrophies) in size and function after puberty, largely disappearing by adulthood. This involution is a classic biological example of a developmental change categorized as the disappearance of an old feature.

The incorrect option is 2: Baby Hair. Baby hair (lanugo or vellus hair, and often the first hair on the head) is typically shed and replaced by mature hair over time. This shedding and replacement process clearly falls under the developmental disappearance of an old feature.

The incorrect option is 3: Temporary Teeth. Temporary teeth, or deciduous teeth, are shed, or disappear, during childhood to make way for the permanent adult teeth. The loss of temporary teeth is a quintessential example of the disappearance of an old feature in the context of physical development.