Instead, it tries to understand why all humans are vulnerable to each disease. It asks how it is possible that natural selection can shape the eye or heart or brain but cannot eliminate our vulnerabilities to nearsightedness, atherosclerosis, depression, or cancer. Darwinian Medicine applies the advances that have revolutionized evolutionary biology to the problems of medicine and tries to provide, for each disease, an explanation for why the body isn't better. Defenses are often confused with diseases. Knowing the difference is crucial, because interfering with a defense is often unwise.
Fever is a defense that protects against infection.
The low iron levels associated with infection are the body's way of keeping iron away from invading bacteria. Nausea and vomiting and diarrhea are useful ways to rid the body of infection and toxins. The nausea that accompanies pregnancy discourages the mother from eating toxic substances that may harm her baby. Even anxiety and sadness can be useful. As for the runny nose that accompanies colds, we don't yet know if it benefits us or viruses, but we certainly need to know in order to decide if nose sprays will help or harm us.