One of my online friends, SirMoogie, sent me an interesting question and I thought I'd post it along with my response:
"A friend and I are having an argument over what the target of selection is. Neither of us are actually biologists, so I don't think we should be discussing this. He read one philosophy on the subject, "Towards a New Philosophy of Biology", by Ernst Mary. Anyway, apparently this is still a contended issue. He says their are three possibilities, the genes, the individual, or the population. The way he described the problem is that the target of selection is that what determines what gets passed on. I responded I don't see why these are mutually exclusive, and that it looks like all of them could have an impact. He says it's the individual, mostly because one philosopher has said so. Have you encountered this issue before?"
My best guess would be that the debate is not overwhether any of these types of selection occur, but over how important a role each level of selectionplays (There is an exception, John Maynard Smith attacked the theory of group selection in the 1960's).
Here's why I think this: You may have heard of the evolution of sickle cell disease. As you know, you getone copy of each gene from your parents, so you have two copies of every gene. People who have one sickle cell gene and one normal gene are resistant to malaria and are essentially normal people. As you probably guessed, these genes are most common in areas wheremalaria is the greatest threat. Anyhow, that seems to me a good case of selection at the gene level. As you may know, people born with two copies of the sickle cell gene have horrible illness and usually live shorter lifespans than other individuals. In this case, it is not the gene being selected against so much as it is the individual. As for group selection, I haven't studied much on that, so I cannot say.