How did diseases evolved in humans.
Why humans get sick? The medieval people believed it was because of bad odours and sometimes our sins, Greeks thought that if a person had a fever he must have too much blood in his system and thus, he must bleed to recover. Then Louis Pasture came along and proved that cholera is actually caused by microscopic germs and not by the sun, comets or too much oxygen! Since then, the science of disease etiology developed to explain and treat diseases. However, this hype in the germ theory and modern medicine could not explain all the causes to diseases, so Darwin’s evolution theory came along to give us a better perspective in trying to assess health and disease in what is now known as evolutionary medicine which correlates natural selection to the causes of current diseases.
In trying to seek a plausible explanation to why fever happens when we have flu for example; scientists found that our lizard ancestors are to blame for this inconvenience! Studies showed that infected ‘cooled blooded’ lizards used to move to warmer places in an attempt to increase their body’s temperature to fight illness. This may explain the evolution of elevated body temperature in humans as a way to fight and destroy pathogens when catching flu. It also suggests that when we take medications to reduce our fever, we are actually intervening with our body’s natural way in fighting infections!
In the process of natural selection, traits are under selective pressure to maximise the individual ability to survive. A famous example is antibiotic resistance of pathogens like tuberculosis (TB). Essentially, pathogens who can adapt when exposed to antibiotics stress in humans will pass their superior traits and will develop a generation that is antibiotic resistant. In other words it is us and our misuse of antibiotics that helped in creating more resistant pathogen strains that are difficult to control and handle by medication.
There is no doubt that evolutionary medicinegave us the historical basis in explaining the existence of disease in humans. It helped to shift the focus of contemporary medicine to the reasons that caused the development of diseases. This will produce improved medications and preventive measures to effectively target disease and pathogens in the next century.
In the concluding pages of Darwin’s book ‘Origin of Species’, he predicted that his work would lead to more important research in the future and it seems that he was right and his envision is being fulfilled. Evolutionary medicine has become a major research discipline in its own right and is helping to bring evidence-based discussions to unlock the mysteries behind today’s most baffling diseases.