Why do chihuahuas have big heads when born?

Chihuahuas are born with relatively large heads in proportion to their bodies due to their genetic makeup and the way their skulls develop. This trait is common in many small Dog Breeds and is a result of the need for the brain to grow and develop properly. The larger head also accommodates the breed's distinct features, such as their large eyes and expressive faces. As they grow, their bodies catch up to their head size, leading to a more balanced appearance.