Here's why:

* Stem cells are present throughout life: Stem cells are found in both immature and mature animals. They are essential for growth and repair, and their differentiation is a continuous process.

* Types of stem cells: There are different types of stem cells, including:

* Embryonic stem cells: These are found in embryos and have the potential to become any cell type in the body.

* Adult stem cells: These are found in various tissues throughout the body and are more limited in their differentiation potential, usually restricted to specific cell types in their tissue of origin.

* Differentiation for growth and repair: Differentiation of stem cells is crucial for:

* Development: During embryonic development, stem cells differentiate to form all the specialized cell types of the body.

* Tissue repair: Throughout life, stem cells differentiate to replace damaged or worn-out cells, maintaining tissue homeostasis.

Example: Adult stem cells are actively involved in processes like blood cell production in bone marrow, skin regeneration, and intestinal lining renewal, even in mature individuals.

Therefore, stem cell differentiation is not limited to immature animals. It's an ongoing process throughout life, ensuring the development and maintenance of tissues and organs.