What is the evolutionary advantage of endemic diseases?
They are widespread in all populations, thus necesitating an evolutionary advantage of sorts. They are not in decline, thus the weak are not dying off (as they should be biologically). So doesn't the logical progression point to an advantage to endemic diseases?
Am I missing something?
Is this a flawed syllogism?
--Apollo
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1. Characteristics that are widespread in a population (at a constant rate over time) necessitate an evolutionary advantage. 2. Endemic diseases fit the aforementioned criteria. Conclusion: Endemic diseases must have an evolutionary advantage to humans. - This doesn't make sense to me, but I can't find an obvious flaw. If the diseases are not noticed (or not heeded) until past reproduction, then the animal may pass on its trait. Endemic diseases often are genetic traits that become expressed at a later date, sometimes after the reproductive period of the animal. For example, we could consider Alzheimer's endemic, but it really only occurs after people have reproduced (except in rare instances). Of course, I believe there are tests out there to find out if you have a chance (stress, "a chance") of getting Alzheimer's or even of being a carrier, but these tests are not 100%, and often they are cost prohibitive. The best we have to go on our vague hunches following ancestral patterns. Even still, many diseases are affected environmentally. If we are to consider autism a disease it may be caused environmentally, and thus, even though the parents may have had perfectly viable genetics, their offspring will undergo a change prenatally to alter genetic viability. Even so, you couldn't really classify every trait humans have as being evolutionarily advantageous. Take, for example, blonde hair. There is nothing special about blonde hair (except perhaps, in some societies, preferences), and yet it fits your definition of endemic. In conclusion, I would say that things that are evolutionary advantageous are prone to be more widespread throughout the population, but the converse is not necessarily true. Well, that doesn't quite make sense. 1. Individuals that are affected by a disease would often die out before reproduction, thus not passing down the disease. Let's say 50% of people (1000 people) express it BEFORE reproduction. 2. Those who express it after reproduction would die out as well. That 50% (1000 people) would die off. 3. So now this disease os HALF as prevalent as the F1 generation (500 people). 4. The next generation would have half as many (250) diseased. 5. The next would have 125. 6. Eventually, the disease will have been eradicated. - Now you might pint out that people have more than one offspring, but both those who express it before and those after BOTH have multiple offspring, offsetting each other and mating declining ratios. Even still, many diseases are affected environmentally. But then those who die of these disease because they don't have gene X would die off, and eventually, only people with Gene X would survive. There is nothing special about blonde hair (except perhaps, in some societies, preferences), and yet it fits your definition of endemic Yes, but having blond hair does not negatively affect an individual. Diseases do. So something with no effect (appendix for example) will remain despite not having an effect, but if it has a negative impact, it should be in decline (and thus not endemic). 1
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It could possibly be evolution's way of balancing itself: creating a finite population to help level the competition of limited resources possibly. Or it could be a variation in our cells that leave an opening for greater change through outside changes; maybe if there's major alteration in the environment than it would be easier for mutations to occur and save the race thanks to the opening by an endemic disease. Then again, it could just be a step toward a greater mutation or a way for us to develop resistance to certain bacteria or radiation... or it could just be because we're really, really unlucky. |
