Blological evolution is the process by which populations of organisms change over time. How could natural selection lead to evolution?

Natural selection is the process of nature selecting the fittest animals to survive and/or thrive, making the weaker ones die out. Over time, the animals with the stronger traits will evolve and adapt to its needs.

Explanation:

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.