[Solved] Discuss some of the various theories relating to the emergence of the three major characteristics of humanness. Be sure to list these characteristics as well. Sinoatrial Node: A group of cells in the right atrium of the heart that initiates the electrical impulses determining the heart rate, often called the heart's natural pacemaker. Atherosclerotic Changes: Alterations in blood vessels characterized by the accumulation of fatty deposits along their inner walls. Internal Bleeding: Bleeding within the body that can result from injury or illness, potentially leading to serious health complications without immediate treatment. Perfusion: The passage of fluid through the circulatory system or lymphatic system to an organ or a tissue.