Explanation: because carry out all the functions in the human body necessary for living. Proteins make up hormones that are required for living. Insulin - responsible for stabilising blood sugar. Haemoglobin - responsible for carrying oxygen around the body. Melatonin - responsible for helping us get to sleep. Adrenalin - responsible for the flight-fight-freeze response. There are many more but here are just a few.
It was the type of diversity that had to do with the niche depending on which niche you are is the amount of varaiaton in your gene pool
Vestigial structures are taken as an example of evolution because they give us an indication of structures that, due to the adaptation to the environment, disappeared.
At the end of the vertebral column, we have the coccyx as an example of this. Its believed that it could have formed a tail and currently, is only a small bone without any specific function, even some individuals are born without it.
A therapist seeing Cheri would attribute her anger to biological factors.
Her angry outbursts happen because of a malfunction in her body. Because her thyroid gland is overactive, this leads to her being angry from time to time if she doesn't take her medicine. Thus, these can only be biological factors, not social or psychological.