Why are Selfish Genes Selfish?

Oct 31 2011 Published by under Uncategorized

Mutations are a fact of life.  Heh, indeed mutations are required for diversity of life.  There really isn't another way to get novel changes to DNA or RNA without it.

I think we can all agree that RNA strands are not alive... in the same way that viruses are not alive.  But they do exhibit some of characteristics of life.

If you will allow me a brief diversion: While I was teaching, a student asked me what the purpose of life is.  Without hesitation, I said, "reproduction".  Of course, the 14-15 year old boys in the class thought that was hilarious and the student seemed quite put out. (I suspect she was attempting to elicit a philosophical point in a science class that she could badger me with.)  All living things die, I explained.  However, when an organism reproduces, it gives some of its genetic material to its offspring.  In that minor way, that organism can influence all future life on the planet.  If an organism dies without passing on its genes, then those genes are lost forever.  There could have been a human 25,000 years ago that was born immune to HIV (not that HIV existed back then, but that's not the point).  If that human didn't reproduce, then its unique ability to be immune to HIV was lost and it will likely never reappear in the world.

This was before I learned that there was an immunity to HIV in the human population.  It's basically the selfish gene concept.

But are genes really selfish?  Obviously, they aren't 'selfish' in the human emotional way.  But, the gene that reproduces the most gets more offspring out in the world and becomes a larger percentage of the total genes in the population.

When I was in high school, I used to say that the human species is breeding for football players and cheerleaders.  Actually what we're breeding for is sex craving men and easy women.  It's true.  I had my first child recently (several years ago), yet most of my high school classmates have multiple children, all much older than mine.  In fact, there are two grandparents from my graduating class.  My genes are being out competed in the human population (which is not really a bad thing considering my genes).

So, its not selfish, it's just better at spamming the environment with copies of itself.

I was going through my abiogenesis papers to find something interesting for you.  I found this. Dr. Joyce does a lot of neat work and although not really an abiogenesis researcher, he has made some interesting discoveries in the field.  This paper describes an experiment in which the experiment was destroyed because of a 'selfish' RNA.

In vitro evolution experiments are very cool.  Basically, you take a RNA (or DNA) and amplify it using a reverse transcriptase and a polymerase that are known not to make perfect copies.  One of my favorite articles using this technique is also by Joyce. The object (as shown in Darwinian Evolution on a Chip) is to evolve a sequence that is better for particular function.

But, something to be careful of is mutations that cause selfish RNAs to appear.  In this case, RNA Z appeared.  This new RNA was successful in competing for resources in the reaction, yet did not perform the desired function at all.

In other words, it is a more successful replicator, but not more successful at doing what it was supposed to be doing.  In this case, it even has evolved some modifications to get around the system that Dr. Joyce used to prevent such a thing from happening.

In this experiment (as I understand it), the desired target product was also necessary for the continued replication of the RNAs.  RNA Z got around that.  I'm sure the paper explains it, but I am not up to that level of biochemistry.  The paper contains a diagram showing how the substrate and promoters and RNAs and DNAs all interact.

After reading this, I am reminded of Jurassic Park (the book, not the horrid movie).  Life finds a way.

Again, this just serves to emphasize our inability to truly separate life from non-life in a meaningful way.  We can't draw the line here anymore than we can draw the line somewhere in a ring species.

8 responses so far

  • EEGiorgi says:

    Great post, I really enjoyed it. But please, allow me a little philosophical digression. The thing is, I get a little edgy when I hear that "genes are selfish." If I may, it is a human interpretation of evolution. And, I find, it narrows it down a little.

    "Competing for resources" really depends on the availability of the resources at a certain time and place. Like you correctly pointed out, even if there was an "HIV-immunity trait" millions of years ago, what was the point, since there was no HIV. Or maybe there was and it got extinct, what do we know? The point is, we don't know what we don't know, but what we do know, we tend to reinterpret and give it an intention it never had. We make it causal instead of casual.

    I personally like to think of it more in terms of "landscapes." Think of life as a landscape with hills, mountains, peaks and valleys. You throw a ball--how many paths can it take in such a rugged landscape? Well, Mother Nature threw a handful of balls and evolution defined the paths: some got lost, but some kept going because they kept finding lower and lower potential. Every new mutation, every new gene, every new branch in the phylogenetic tree of life represents a path in this landscape. Some were dead ends. Others, are paths still being explored.

  • I agree totally and I tried to say that. 'Selfish' is a human emotion/behavior. No emotion or behavior can be applied to things without nervous systems. In teaching, I think that it helps students when they are first learning to use analogies like that.

    14-year-olds are good studies of emotion and behavior... not so much the fitness landscape or any abstract model for that matter.

    Anyway, I agree... although I'm not too sure about the lower and lower potential. Though I guess any model or analogy breaks down at some point.

    Some genes survive. If they are more effective at reproduction, then they create more copies than other genes. If they help another gene create more copies and are carried along for the rise, then they would have more copies than other genes.

    It's not selfish... it's population dynamics?

  • EEGiorgi says:

    Yes, but there's a lot more to evolution than "fitness" and "surviving genes." There's epigenetic memory, and jumping genes, and RNA editing, and neural plasticity, and so much more we still don't understand...

    Sorry, you're right, it just that it feels too much of a... box.
    But that's me. And I sit in a cubicle, not in a classroom... 🙂

  • EEGiorgi says:

    In fact, I should also mention neutral theory and the fact that today's belief is that most of selective sweeps have occurred under genetic drift -- we can talk more about this in a separate setting, but one place where to look is Kimura's neutral theory. Basically, if you assume that ALL traits have been selected for, you cannot explain the amount of diversity you see today.

    Sorry, I'll shut up now. 🙂

  • Isabel says:

    "If an organism dies without passing on its genes, then those genes are lost forever." Not if the organism has a lot of relatives.

    Also why are "easy women" selected for? ? Are you suggesting that women do not "crave sex"? Why would that be?

  • Isabel,

    Yes, if the organism has lots of relatives, then those genes may be passed on. There are several studies that show some species do help close relatives (aunts, uncles, and cousins).

    But I was referring to the first genes.

    As for the 'easy' thing... sigh.

    Please keep in mind that is what I said in my callow youth. But the thinking was that 'easy women' would tend to have more kids than women who were not 'easy'.

    There is a significant component of individual behavior that is genetic. So, the genes that result in 'easiness' (in men or women) would tend to propagate more quickly than other genes.

    Culture and society probably play a part in modern human society as well.

  • Joe G says:

    Hi Kevin,

    I can still post in other people's threads and I can expose you for the fraud and liar you are.

  • EEGiorgi says:

    Isabel, Kevin used a very simple example, maybe a bit too simplistic, but the truth behind his comment is called "genetic drift," which, as it turns out, has been a great driving force in evolutionary history. Genetic drift describes the mechanism by which minor alleles can get fixed just because of resampling of the population from one generation to the next. This had a far broader effect back when we were hunters and migrating constantly. Mutations appearing at random would have a far greater chance to "get fixed" just because populations would split, migrate, etc, and in small populations minor alleles have a greater chance to survive. Wikipedia has a nice page on genetic drift:
    http://en.wikipedia.org/wiki/Genetic_drift

    If we really want to make an analogy, these are alleles are really not "selfish," but rather, completely "blind."