Everything Science Forum

How does Darwinism apply to diseases?  Do diseases evolve according to survival of the fittest?  If so, what is the purpose of a lethal disease?  Is it just a misstep in evolution?  I don't understand how a disease that exists to kill its host would help it survive. 

I guess this depends a lot on your definition of disease.  Disease has been used to describe everything from viruses and bacteria to cancers and other genetic factors that cause death, and even protein malformations like BSE.

From your post, it sounds as if you are referring to diseases as living organisms, which is not necessarily the case.

I guess I should have used the word virus.  I was reading about the 1918 Influenza pandemic on Wikipedia when I first wondered this and that was the kind of disease that I had in mind.  From what I understand, that strain simply died off after killing millions of people. 

Ah.  OK.

It is still questionable whether or not viruses are living organisms.  They do not contain DNA;  Instead they have RNA, which cannot replicate without a DNA-driven host.

The influenza pandemic of 1918 did not end in the demise of the flu.  Influenza type A (aka the Spanish Flu) is alive and well, but people who die from infection by that virus are very few (though it did reach what were considered pandemic proportions again in 1957 and 1968) [ Source (http://www.cdc.gov/ncidod/EID/vol9no10/02-0789.htm) ].  This is due in part to advanced modern medicine, the fact that people who were genetically pre-disposed to dying from that infection in 1918 would have very few living descendants, and the fact that people who were genetically pre-disposed to having stronger immunity against that virus would have lived to have more children. So a pandemic of that particular virus is unlikely if not impossible, even though the virus is still around, and even though there are still a few people who die from it.

Despite that, the process of evolution does not necessarily infer the advancement of a particular species -- Darwinism does not guarantee the success of any mutation in any environment.  There is no logical optimization from one generation of organisms to the next.  The only real optimization in evolution is the extinction of a population or a whole species due to its inaquedacy in its environment.

To use another virus example, let's look at the "chicken flu".  This virus is able to spread from chickens to humans, and may be fatal.  But, it lacks the ability to spread from human to human, and the mutation required to the virus to allow it to do that is highly unlikely.  In fact, the odds of the virus mutating into something that is harmless to humans is more likely.

Interesting stuff Orstio.

the mutation required to the virus to allow it to do that is highly unlikely.

The governments would have you think otherwise...  ::)

The governments would have you think otherwise... 

Actually, I think it is mainly media hype, and I'm glad that the WHO is actually not playing into that with the chicken flu.

http://www.who.int/csr/2006_02_20/en/index.html

Assessments of the outbreak in Turkey, conducted by WHO investigative teams, have produced no convincing evidence that mutations have altered the epidemiology of the disease in humans, which was similar to the pattern consistently seen in affected parts of Asia. There is no evidence, at present, from any outbreak site that the virus has increased its ability to spread easily from one person to another.

Well, In England the health minister said that thousands will be killed as a matter of fact. Some medical companies might not mind the media hype either...

can't find the link, but here's a similar story:
http://news.bbc.co.uk/1/hi/scotland/4306261.stm

That's nasty.  I would hope from the big SARS scare not so long ago, that governments would be more cautious about making such atrocious predictions.

Well, unfortunately, politicians are not trained in medical issues, but they are held responsible for the general welfare.  What would happen if there was an outbreak of some strong variety of flu, but the government was not prepared.

The other part of it is that it seems that some medical personnel are concerned and sufficiently worried to make extraordinary warnings (actually they just don't know).  This is complicated by the contaminated flu vaccines last year and a reduction in supply.

Really, they should just emphasize good hygiene practices.

On the matter of flu mutation, I think that varities do survive in 'carriers', e.g. birds, animals (pigs) and people.  There may be some mutation, but most are not significant.

Just wash hands, and stay away from people who are coughing and sneezing, particularly if they are not covering their mouths and noses.  I've already had some friends come down with some nasty colds.

Thinking about the original questions, "How does Darwinism apply to diseases?  Do diseases evolve according to survival of the fittest," Darwin's theory of evolution would apply to survivors of the illness.  Those susceptible to a virulent disease die off, those with good resistance survive.

Besides humans, there are birds or swine and perhaps other animals in which the virus survives and circulates.  I think each factor (human, bird, animal) are intermediates.  Humans are perhaps not naturally part of the normal cycle, but rather just get infected and become ill or die.