Mosaic evolution represents a natural selection process. It acts on different structures at different rates, depending on the needs of a species.
Mosaic Evolution -- Definition 1Edit
When evolutionary change takes place in body parts/body systems of an organism without simultaneous changes taking place in other.
Mosaic Evolution -- Definition 2Edit
Characters evolving at different rates within and between species.
This can be observed in the development of traits in elephant species. In African elephants, the forehead shortened early on, while the molars became modifed later. Meanwhile, the Asian elephant had little shortening of the forehead, while early on the molars rapidly modified.
Mosaic Evolution. (2013). Encyclopaedia Britannica, Inc. Retrieved from http://www.britannica.com/EBchecked/topic/393342/mosaic-evolution