why are there so many diseases

Question: why are there so many diseases
- Keywords:
  disease
Asked by sciencebox to Sarah, Tom, Tim, Derek, Dalya on 19 Jun 2011. This question was also asked by mizzpinky786.
- Dalya Soond answered on 13 Jun 2011:
  
  Because we have so many molecules that make our bodies work, and any of these molecules can go wrong.
  
  But actually, I think an equally interesting question is: Why don’t we have MORE diseases?
  
  It’s because Nature is very clever and comes up with many ways to stop diseases. For instance, if a cell makes a mistake when duplicating it’s DNA before dying, the cell will sense that mistake, and freeze the cell before it continues dividing so it can try to fix the mistake. If it can’t fix it, it will force the cell to commit suicide so that the cell cannot go on to form something like cancer. If the cell doesn’t die and cancer starts to develop, the immune system can try to kill those cells as well.
  
  There are other molecular mechanisms as well to protect against disease. For instance, often you have 2 or more proteins that can do the same job so if one is ‘broken’ the other can take over.
- Derek McKay-Bukowski answered on 13 Jun 2011:
  
  Humans are complicated. There is a lot that can go wrong. Also, there are lot of bacteria and viruses out there to attack us and they have evolved into all sorts of different strains, in the same way that there are lots of different types of animals and plants.
- Tim Millar answered on 13 Jun 2011:
  
  Infection and Immunity. Lots of organisms all trying to survive in the same place means there is competition so to survive you have to beat the competition or use them in a way to spread yourself over a wider area. So for viruses and bacteria their natural habitat is in us. We respond to infection and damage ourselves in the process. Our own immune system turns against us and in extremes starts to attack itself. Over time we have been able to control the ammount of infections so that we have evolved to where we are now. With the help of vaccination and other drugs, maybe we are at an advantage above and beyond where our evolution has brought us as we can outwit some bugs like small pox and polio.
  
  Age. Many diseases are of old age. Most organisms live long enough to reproduce. If we lived long enough only to reproduce, many diseases of age would not be seen such as Alzheimers, most cancer and arthritis. This extra time means that the bodies ability to look after itself and repair damage from the environment is lost the older we get.
  
  Genetics. The make up of our DNA is important with mutations leading to disease.
  
  Lifestyle. Some diseases are related to how we want to live our lives such as lung disease from smoking and pollution or heart disease and diabetes from bad diet. These diseases are preventable and if we changed our habits, there may be less disease than we see at present.
- Sarah Thomas answered on 13 Jun 2011:
  
  I think that one of the reasons that there are so many diseases is that bacteria and viruses are evolving so fast. They can evolve to become immune to our medicines, evolve new strains that we’ve never seen before.
  
  And I think the points that Tim made about age and lifestyle are absolutely correct.
- Tom Crick answered on 19 Jun 2011:
  
  Some great answers already, but it’s quite interesting to think of diseases at things that deliberately attack humans — we are not special in the big scheme of things and these diseases (bacteria, phages, viruses, etc) are just doing what they do to survive and propagate.
  
  However, as we have designed drugs to combat these diseases, we have unwittingly created more resistant versions, or even completely new ones!

Question: why are there so many diseases

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