It should be natural selection since there is no external influence implied. (like environment or genetic mutations.)
Answer:
Your digestive system absorbs water and nutrients from the food you eat. Your circulatory system carries oxygen, water, and nutrients to cells throughout your body. Wastes from the cells are eliminated by your respiratory system, your excretory system, and your skin.
Explanation:
Answer:
What?
Explanation:
I don't understand the question.
Which structure are you talking about??
