<span>The answer to this question would be: tissues; decrease
Oxygen is delivered to the tissue by the heart. It will be unloaded in the tissue, causing the oxygen level in the blood to be decreased. After that, the blood also picks up the carbon dioxide so its level will be increased.
In lungs, the carbon dioxide will be unloaded and oxygen will be loaded back into the blood.</span>
The reason is that of the significance of the brain in human existence. In biology, the traits that provide an advantage in the environment are preserved and improved upon. Therefore, as humans continue to use their brains to influence their environment, as the society rewards those with higher intelligence (associated with bigger brains),the bigger brains will be favored by natural selection.
