In order for natural selection to take place we must have "variety in a population". This variety of traits is what allows natural selection to "pick" the most favorable traits.
Explanation:
during the embryonic stage the baby grows its organs
Nervous system. This is one of the first things that develop. It includes the formation of the baby’s brain, spinal cord, and nerves.
Heart. An S-shaped tube forms on the front of the embryo. This will become the baby’s heart. At first the heart does not beat, but soon it starts beating and pumping an early form of blood.
Face. The baby’s facial features begin to take shape. The eyes and ears form. The eyes move forward on the face, and eyelids form. Pieces of tissue grow and join together to create the forehead, nose, cheeks, lips, and jaw. The nasal passages, mouth, and tooth buds form the baby’s first teeth. A tongue with taste buds also forms.
Arms and legs. At first, the baby’s arms and legs begin as little buds that sprout from the embryo’s sides. As they grow, the arms look like paddles and the legs look like flippers. A ridge appears on the end of each one. They eventually become the baby’s fingers and toes.
Sexual organs. Cells form to become the baby’s eggs or sperm. The baby’s private parts (girl/boy) is visible at the end of the embryonic period.
Muscles and movement. Muscles develop and the embryo begins to move. At first it’s only twitching and reacting to touch. Once the nerves and muscles start working together, the baby can start moving on purpose.
the frog is now a predator
