What is one key characteristic of stem cells?

Stem cells are unique due to their ability to self-renew and differentiate into various cell types. This means they can replicate themselves many times while also having the potential to develop into specialized cells, such as nerve cells, muscle cells, or blood cells. This characteristic is crucial for growth, development, and tissue repair in organisms.

The notion of self-renewal ensures that a population of stem cells can persist over time, allowing for continuous replenishment of the body's cell types. Differentiation allows for the specialization needed for various functions within the body. This versatility is why stem cells are a significant focus in medical research and therapies, as they hold the potential for regenerative medicine and treating a variety of diseases.

In contrast, the other options describe aspects that are not correct regarding stem cells. For instance, stating that they can only develop into muscle cells or that they are fully differentiated misrepresents their capabilities, and suggesting they are found only in embryos overlooks the existence of adult stem cells that serve important roles in various tissues.