Grasping fully evolution and all its implications is not easy. A hot topic on which there has been, and partly there still is, a big debate is the unit of selection.
What do I mean? Think of it in this way: between the whole biological spectrum, from cells to organisms and from genes to species, at which level does natural selection act? What is the elementary unit that is positive or negative selected by nature?
Maybe with an example it’ll be clearer. Why did natural selection select herd formation in gazelles? Well of course when together they do better because the single risk of predation is lower compared to a guy wandering in the savana by itself. But who actually get the benefit of evolution?
From this example the theory of group selection was formulated. The herd behavior can be explained as overall benefit for the whole group! Every gazelle will group together with others for the good of the group. The advantage that every single individual gets is not very high because living in groups also has many costs (sharing food area for example) but the behavior benefit the group consequently the behavior would be selected.
The group selection theory helps us explaining also other behaviors but is generally problematic and thus it’s not considered a predominant explanation if not only for a few case. But the Idea is: I might as well sacrifice myself for saving my group thus increasing the chance of its survival. People speaks even of species selection if we’re talking of the good of the species. A more accepted theory for origin of “weird” behavior is kin selection (see Hamilton’s rule post for more details).
But there are other theories out there, that are, honestly, even more intriguing than the group selection theory. On the other side of the spectrum, and as a molecular biologist it makes me tingle inside, there is the gene selection theory. If you think of any heritable trait, from behavior to physical appearance, this must be determined by a, or some, gene/genes. So actually, it’s the gene which is being selected by natural selection to favor the development of useful trait! Any trait useful for the individual or the group or the species is determined by a gene which is being selected inside us.
I’m sorry but I have to go further. A popular guy named Richard Dawkins has pushed this forward, he talks about the selfish gene theory. And this is where the jaw Drop comes in.
Let’s think for a moment that species are not driven by instincts and thoughts to feed and reproduce but instead selfish genes inside your body use you as a vehicle to promote their own reproduction. Yes that’s the theory in a nutshell.
Think every gene in your body in constant struggle with others alleles to reproduce in the next generation. Now, it’s in its own gene interest to promote and guarantee the survival of its vehicle, otherwise it couldn’t produce more copies of itself for the next generation. So not only the gene is selected by natural selection but genes are being “selfish” promoting useful traits in nature to get passed down the generations.
As amazingly mind-blowing as it sounds this theory seems to have some truth. It can explain a lot of stuff, including most of the stuff group selection does.
Think now that I want to form an herd because, instead of helping my group, I want to shield myself behind others. Genes that promote this behavior want to reproduce so they will be selected to favor the herd forming, called selfish herd unsurprisingly.
So we said that a selfish gene wants to pass down to the next generation. How can it do that? One way is the one we already explained: promotion the survival of its vehicle. But it could do it in another way: promoting the survival of close enough relatives that share most of the genes. This may seem even crazier but it works. If, instead of saving myself, I save two brother or 4 cousins I will pass down to the next generation the same amount of genes! (see Hamilton’s rule post for a more formal description of this.) And also I can even help you if you’re not my relative, but you gave to guarantee me that you will help me back.
Evolution is a whole story to explore and many of its actors are crazy and surprising. Do you think you’re driven by selfish genes always struggling to reproduce or do you think you’re behaving for the good of your group??
Maybe it’s something completely different! In the meantime let me tell you another story..