Why do our organs have so many reserves?
The likely answer is evolution: early humans with a genetic make-up capable of producing organs with spare functional space could survive, reproduce, and reproduce better than others without this genetic make-up. As a result, genes associated with excess organ capacity—remember: two kidneys, not one—are more likely to be passed on to future generations.
At the same time, evolutionary ancestors without as many reserves may not survive long enough to reproduce and therefore fail to successfully pass on genes. Over thousands of years, this force of natural selection has given modern humans a well-stocked range of organs.
Eyes, liver, lungs, etc.
Here is just a partial list of body parts, there are plenty more in store:
- Eyes: One eye will keep you fully healthy, although you may miss out on the depth perception and wider field of view that two eyes provide. Even losing an eye does not directly lead to poor health, although blindness clearly creates challenges and affects quality of life. Additionally, research suggests that severe visual impairment may increase the risk of Alzheimer's disease.
- Ears: While having two ears allows us to localize sounds coming from all directions, losing hearing in one or both ears does not immediately affect overall health. But like vision loss, hearing loss can also reduce quality of life. As with vision loss, recent research shows that people with hearing impairment are at higher risk for cognitive problems.
- Intestine: Relatively large portions of the small and large intestine can be removed without significant impact on your health. In fact, the entire colon can be removed (a procedure called a total colectomy) without shortening a person's life, although diarrhea or other digestive symptoms may occur. Removing part of the intestine is a relatively common surgery (for example, for colon cancer), but removing part of the intestine does not in itself harm health or shorten life.
- Kidneys: Most people can live quite well with just one kidney. This is why people can donate kidneys to those in need. However, the remaining kidney has to work harder, and the risk of future kidney failure does increase. In addition, injury, infection, or other conditions affecting the remaining kidney may lead to kidney failure sooner than usual.
- Lungs: If necessary, the entire lung can be removed and you can rely on the other lung, which functions just fine. The lung may be removed because of a tumor, but occasionally it may be removed because of infection or emphysema.
- Liver: A relatively large portion of the liver can be removed (assuming the rest of the liver is healthy) because there is a lot of "reserve" liver tissue and the liver has the ability to regenerate.
Does this mean that many parts of our bodies are indeed expendable?
perhaps. If you were only thinking about survival, you might view many of our body parts as expendable. In fact, you can survive without your spleen, most of your liver, eyes, ears, lungs, kidneys, and other parts.
But clearly there are other factors to consider besides survival, not least quality of life . Therefore, no one would suggest giving up even the most useless organ without good reasons.
Fortunately, our organs have so much reserve: millions of people around the world owe their survival to having so much redundancy in our organs. Living organ donors can give up part of a kidney or other organ to help others live better and stay healthy.
So even if some parts aren't absolutely necessary, it's good to know there are so many in stock available. You never know when it will come in handy.