The doggy position is one of the most basic position. It is a position where quadrupedal animals copulate. Bipedal animals such as men, can simulate quadrupeds just as quadrupeds can simulate bipeds by standing on their hindlegs. The name doggy-position came from that of dogs, the most common quadruped in contact with men in modern times.
Have you seen a Buddha sitting on a lotus? You know, sits on the butt with legs in a intertwined crossing such that the right foot rests on the left thigh and the left foot rests on the right thigh, with soles facing up. Such a sitting position is called the lotus position. It is also one of the most basic posture of yoga, and does take some flexibility and getting used to.
If a man assumes a lotus posture and a woman sits on the penis of the man, then that's the lotus sex position. That'd be the ultimate zen of copulation. In the illustration above, the boy kneel instead, which decreases penis exposure and does not provide a flat surface for the woman to sit on.