Answer:
Parathyroid hormone increases the level of calcium while calcitonin hormone decreases the level of calcium in the blood.
Explanation:
Parathyroid hormone is a type of harmone which is responsible for balancing calcium in our body. When the calcium level lowers in our body, parathyroid hormone is secreted and calcium is absorbed from the bones and fullfilled the requirement of the body. If the tumor secreted calcitonin hormone instead of parathyroid hormone, the calcium level in the blood is lowered because it acts to the opposite of parathyroid hormone.
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
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