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I know there are a lot of diseases that can be cured or greatly aided by going paleo, and i am all for trying to get people to believe that their ancestors didn't eat genetically modified 80+% starch corn and HCFS, but i think that our genetics also plays an opposite role with the advent of agriculture.

My reasoning is that with the advent of agriculture, genetic lines that would otherwise end due to weakened bodies or the lack of a chance to reproduce before death were suddenly able to reproduce, and diseases that would otherwise rarely, if ever, show up are now showing up more and more due to, in part, our lack of natural selection? Thoughts?

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With the rise of agriculture, natural selection didn't stop! The selective pressure just changed. A lot. And very fast.

But I don't know how this could contribute to the spread of some truly genetic diseases. So your question is a good one.

Maybe worth mentioning is that sometimes diseases (or at least having one gene that codes for the disease) could have a darwinian benefit. Sickle cell anaemia is most cited example. If you carry one gene, it protects you against malaria. If you have the two genes, you have the terrible disease. Indeed, sickle cell anaemia is prevalent in (West) Africans and their descendents.

Another possible example could be the lethal disease cystic fibrosis. People carrying one gene could be better protected against cholera.

This kind of reasoning is typical for evolutionary or darwinian medicine. Google if interested...

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@ pieter d: +1, great answer! The selective advantage of heterozygotes is one way a genetic disease becomes common. Another way is if the mutation itself occurs commonly. This is the case with neurofibromatosis type 1 (NF-1). Although the abnormal NF-1 gene is dominant, about 1/2 of all cases occur due to new mutations in the NF-1 gene. So even though there is no known reproductive advantage to having NF-1, there is a constant supply of new cases due to fresh mutations. Ref: ghr.nlm.nih.gov/condition/… – Ed♦ Sep 10 2010 at 1:45

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