<span>Gametes serve two functions. They have the physiological capability to fuse with a gamete from the opposite sex and form a single cell (a zygote) that initiates the development of a new organism and the next generation. They also carry a complete set of genetic instructions that this new organism will need to grow, develop and complete its life cycle. Gametes are made from the cells of an organism through a special division process called meiosis (see other lesson). This cell division process allows the gametes to have half of the genetic material of the original cell. The genetic material is packaged in structures called chromosomes and the chromosomes sorted in an orderly fashion to give each gamete the one set of genetic instructions. Offspring made from sexual reproduction will have two sets of genetic instructions, one delivered from the male gamete (pollen in plants, sperm in animals) and one from the female egg.</span>
Answer: The literal reason would be because our ancestors did. The ancestors of all modern mammals had five digits on each limb up to 360 million years ago.
