Before the diving reflex begins, three critical changes must occur in the body to stimulate the diving reflex. The first to occur is the change in heart rate, this happens immediately when the face comes into contact with cold water, the human heart rate slows down by 10 to 25%. Seals, for example, experience extreme changes in their heart rate, from about 125 beats per minute to as low as 10 in a prolonged dive. (Arterial gas tensions, 1989). Slowing the heart rate reduces the need for oxygen in the blood, distributing more of it to be used by other vital organs. Following changes in heart rate, peripheral vasoconstriction occurs, which consists of the narrowing of blood vessels to reduce blood flow and is achieved through muscular contraction of the blood vessel walls. This decreases the amount of blood flowing to peripheral organs that do not require a high level of oxygen to function. This is the prevention of blood circulation in certain areas, the first to be closed are the toes and fingers, then the hands and feet, and finally the arms and legs. The constriction allows more blood to be used by the heart, brain and organs. Finally, the movement of blood which only occurs during very deep dives. When this happens, the walls of the organs and the circulatory system allow plasma and water to pass freely through the thoracic cavity, so its pressure remains constant and prevents the organs from being crushed. In this phase the pulmonary alveoli fill with blood plasma, which is reabsorbed as soon as the animal leaves the pressurized environment. This phase of the diving reflex has been observed in humans such as deep diving divers, who can reach distances of approximately 90+ meters. Therefore, both a conscious person and an unconscious person...... middle of paper ...... survived without any harm, but this shows that Gore's internal mechanism saved his life. The same goes for divers who dive to depths: the extreme processes of being able to get to those depths and survive. Deep diving represents the specific adaptations that some animals have had to undergo in order to reach great depths without equipment and help. Extreme deep diving records have been broken that demonstrate the adaptation of the human body to certain pressurized environments with practice, which could lead to physical changes in the body to be able to do without diving equipment. These examples are great examples of how evolutionary adaptations directly impact the survival of both humans and animals. Mammillary diving responses are a direct force of natural selection that is continually evolving to ensure the survival of the fittest.