Why do we have different skin colors?

The color of a person’s skin depends on his environment. In regions with abundant sunlight, a dark skin color is necessary to provide protection against the harmful UV rays. Light-skinned people in north Europe, where there is very little sunlight, do not need this protection. UV rays are  not always harmful: they are needed for the formation of vitamin D, which the body needs for building bones. The darker the skin, the less sunlight can enter the skin and vitamin D formation is reduced. A dark skin may, therefore, result in Vitamin D deficiency in areas where there is not much sunlight.

Why can’t we tickle ourselves?

The skin , as a sense organ, perceives all kinds of touch sensations as signals. These signals are sent to the brain, are interpreted, and the body reacts accordingly. The brain can differentiate between the touch stimuli that we create ourselves and the stimuli given by others. If we try to tickle ourselves, our brain anticipates this type of touch from our hands and prepares itself for it. Since the element of unexpectedness is missing, the body does not respond the same way as it would if someone else were to tickle us.

How can people be identified with the help of fingerprints?

Just as each human being is unique; his grooved fingertips are also unique. Even identical twins do not have the same patterns of grooves on their fingertips.  Minor cuts and some skin diseases may cause temporary changes in the patterns , but on healing, the same pattern appears. Since 1901,police have used this knowledge to compare  the fingerprints found at a crime site with those of the suspects. In early days, this comparison was done manually and used to be very cumbersome and time-consuming. Today, fingerprints are matched by the computer in a fraction of the time used earlier.