What is the biological reason for black stripe on their skin?

The black stripes on a tiger's skin are due to a pigment called melanin. Melanin is a type of skin pigment that is produced by melanocytes, specialized cells in the skin that produce melanin. The amount and distribution of melanin in the skin determine the skin's color. In tigers, the stripes are caused by bands of increased melanin production in the skin.

The primary function of melanin in tigers is camouflage. The black stripes help to break up the tiger's outline and make it more difficult to see in the dense forest vegetation where tigers live. This camouflage helps tigers to avoid predators and prey alike.

In addition to camouflage, the stripes may also provide some protection from the sun's ultraviolet rays and help tigers to regulate their body temperature.