There have been a spate of articles about E. O. Wilson'sdrive to put group selection back into mainstream conversation among evolutionary biologists over the past year. Wilson has kept the torch alive for this particular paradigm since the 1970s, when it was prominently featured in his famous book Sociobiology. At the same time as Wilson was making waves in the United States Richard Dawkins debuted with The Selfish Gene, a book where he explored the new ideas of theoretical biologists W. D. Hamilton and J. M. Smith. Hamilton's model of kin selection, which he debuted in the mid-1960s, ushered in a revolution in the social theory of evolution and heralded a long twilight for group selectionist theories (the philosophical decapitation was implemented by George Williams). Through this period Wilson refused to be swept away by the swelling tide, and in his book Evolution for Everyone David Sloan Wilson recounted how as a young scientist he was encouraged to explore this topic by the older Wilson.
So what happened to prompt E. O. Wilson to become more vocal? I don't know much about ethology, but when I did poke into the literature a few years ago I stumbled on to some papers which expressed skepticism about the explanatory power of kin selection to explain eusociality among haplodiploid insects. Specifically, consider Hamilton's Rule:
rB - C > 0
That is, the coeffecient of relatedness to an individual times the benefit to that individual minus the cost to yourself must be greater then one for an act to be genetically rational. In other words, if you increase the fitness of your full sibling my more than twice the reduction of fitness to yourself then the act will be genetically favored. For a cousin, you have to multiply the increase by four, because a cousin is only 1/4 as related (coefficient of relatedness 1/8 as opposed to 1/2). Among hymenoptera (e.g., ants, bees, wasps, etc.) the haplodiploid inheritance system implies that sisters should be more closely related to each other than to their offspring. This means that increasing the fitness of a sibling (i.e., a sister queen) might be more genetically optimal than producing your own offspring!
More precisely, drones are haploid, while females are diploid. Full sisters share at least 50% of their genes via their father. From their mother they should share another 25% (remember, the mother is diploid, so she can contribute varied copies). So the expectation is that full siblings will be related on the order of 75%! This makes Hamilton's Rule a lot easier to satisfy. A theoretical problem is that queens may be fertilized by the sperm of multiple drones, which might result in far lower than 75% relatedness. Additionally, not all haplodiploid insects are eusocial, and not all eusocial insects are haplodiploid. This means empirically we always knew that haplodiploidy is not necessary nor always sufficient to produce eusociality. My understanding though is that with DNA fingerprinting entomologists have attained a much finer grained understanding of the relatedness of individuals within hives or colonies, and it necessitates the generation of a more complex picture. This means that though the press loves a fight, this is ultimately a debate about semantics and emphases, a difference of degree and not kind.
Note: Definitions matter here. Richard Dawkins believes it is important to make a distinction between replicators and vehicles. A lot of the popular press pieces are sloppy in that they juxtapose gene level selection and group selection. This means that one is really contrasting meiotic drive with interdemic competition. I really don't think that this is the intent. All selection affects evolutionary change via differential replication of genes, the real debate is about the unit of selection. Also, I have a close friend who is in Wilson's department at Harvard, and from personal communication I can confirm that he has convinced very few of his colleagues at the same institution.
Related: Zooillogix has some comment on this issue. Cooperation and multilevel selection.
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I have no formal training in genetics, and I'm finding that the non-technical discussions of kin selection that I happen to see don't address a couple of points likely to confuse a layman like me.
First, I'm told that I have 1/2 of my genes in common with a sibling, so sacrificing myself for two siblings achieves kin-selection break-even. But then I see headline-grabbing articles stating that humans and chimps share 90-something percent of their genes in common. This suggests that sacrificing myself for only about 1.1 chimps also achieves break-even.
Further, lots of popular articles stress that humans have rather low genetic diversity. So, even in those 50% of instances where my sibling and I inherited some gene from different parental paths, my gene and my sibling's gene should still very often be chemically identical or nearly identical. (My brother and I may have just withdrawn a nickel each from two different banks instead of the same bank, but looking further back, those nickels often turn out to have come from the same mint.) In this sense, siblings must be way more than 1/2 related and cousins way more that 1/4 related. Why isn't this higher degree of genetic relatedness, seemingly more accurate, the proper input for kin-selection calculations?
I guess the resolution of my chimp paradox must have something to do with different definitions being used for "degree of kin relatedness" vs. "degree of genetic similarity with other species." But darned if I can find an explanation of the difference in the popular accounts.
Now my key question: Even if different definitions are in use, __Why isn't genetic similarity, in the sense that we're 90-something percent genetically similar to chimps, the important factor for kin selection?__ If kin selection really occurs, why don't I sacrifice myself for 1.1 chimps?
The next problem is well-known: In a population where all individuals follow kin-selection altruism, a mutation could arise causing an individual to cheat, still deriving the benefits of the sacrifices of others, but never personally sacrificing. That's clearly an advantage that would be passed on. I can understand why kin selection can work well temporarily, but I've never seen a succinct "terms a layman can understand" explanation of why it isn't, in the long run, always unstable due to the eventual rise of cheaters.
If you, or your readers, could address this here or in another blog post, I'd be most appreciative.
When people talk about "sharing half your genes" with your siblings on average, they're really talking about the genes that can vary from human to human and are associated with the traits that distinguish you from other human beings.
When people talk about sharing 90+% of your genes with a chimp, they're talking about the totality of all genes, most of which are the same within all multicellular organisms.
Now my key question: Even if different definitions are in use, __Why isn't genetic similarity, in the sense that we're 90-something percent genetically similar to chimps, the important factor for kin selection?__ If kin selection really occurs, why don't I sacrifice myself for 1.1 chimps?
think of it from a 'gene's eye view.' kin selection works pretty easily. think of a locus, 1, with two alleles, A and B. A gives one a propensity to altruism toward kin and B does not. over time the frequency of A increases because A is more likely to exist in kin than B (from the perspective of the A mutant lineage). obviously kin selection only works in the context of where you aid a conspecific, so genetic similarity to other species is usually irrelevant. this sort of selection can't work when there's no interaction and aid.
The next problem is well-known: In a population where all individuals follow kin-selection altruism, a mutation could arise causing an individual to cheat, still deriving the benefits of the sacrifices of others, but never personally sacrificing. That's clearly an advantage that would be passed on. I can understand why kin selection can work well temporarily, but I've never seen a succinct "terms a layman can understand" explanation of why it isn't, in the long run, always unstable due to the eventual rise of cheaters.
a cheating allele, C, would screw its relatives. those relatives also would be likely to carry C. so summed across the kin group you operate on a zero sum principle (or less than zero sum).
the 90% chimp vs. r=.5 full sibling thing can best be understood by noting the difference between "identical by descent" vs. homology.
"First, I'm told that I have 1/2 of my genes in common with a sibling, so sacrificing myself for two siblings achieves kin-selection break-even. But then I see headline-grabbing articles stating that humans and chimps share 90-something percent of their genes in common. This suggests that sacrificing myself for only about 1.1 chimps also achieves break-even."
This is Richard Dawkin's Misunderstanding No. 5 of kin selection: "All members of a species share more than 99 % of their genes, so why shouldn't selection favour universal altruism?"
See: http://www.simonyi.ox.ac.uk/dawkins/writings/Twelve%20Misunderstandings…
for the explanation.