There is perhaps no more ancient or primitive musical instrument than a pair of "sticks" that are banged together to provide percussion rhythm. It is not known where or when this was first done but probably in Africa at the dawn of human life.
Palitos are usually two cylindrical hardwood sticks approximately 20 - 25 cm long and about 2.5 - 3 cm in diameter. They are played by laying one stick acoss the palm of the hand so that one end rests lightly on the fingertips. This makes the sound of the stick resonate when it is struck by the other stick, which is held between the thumb and first two fingers of the other hand.
Of course, palitos are not unique to Puerto Rican or even Latin American music either. However they are pervasive and widely used in virtually all types of music from folk styles to rumba and salsa. In all of the genres the role of the palitos is the same: primary or secondary driver of the rhythm of the music.
Palitos may be played by tapping them aginst the side of a drum or in another variation, by beating them against each other. The rhythms played with palitos are elaborations on the clave, the same two bar pattern without variation for the entire piece, as demonstrated in this short example of the 3-2 clave.