inclusive fitness stuff

i think inclusive fitness is one of the coolest concepts. ever. it doesn’t explain everything in Life, of course, but it explains a lot. it’s certainly helped me to make sense of why people (most organisms) behave in the ways that they do towards other individuals.

here are some neat examples of inclusive fitness affecting human behavior from robin (ian macdonald) dunbar [pgs. 137-39]:

[T]here is plenty of empirical evidence to suggest that, irrespective of the importance of social kinship, biological (i.e. genetic) kinship does play an important background role in the decisions that individuals make on how they should treat each other. In an analysis of Icelandic Viking sagas, for example, my colleagues and I showed that individuals were significantly less likely to murder close relatives (those related to ego as paternal cousins or better) than less closely related individuals (for a similar analysis of the English kings and queens, see Johnson and Johnson 1991). More importantly, their willingness to murder relatives was modified by the value of the action to the murderer: they were willing to murder distant relatives for trivial benefits (e.g. in a drunken brawl), but close relatives were only murdered if the gains were very high (e.g. by doing so, they inherited an earldom or land). Similarly, the Vikings were more willing to form alliances (or to make loans of ships, supplies, or men for expeditions) with close relatives than more distant ones, and when they did so were less likely either to demand explicit reciprocation or to renege on the agreement later.

“Note that it does not matter much how the Vikings themselves construed their patterns of kinship in these cases: these findings are based entirely on pedigrees constructed out of declared paternities. While the Vikings may have occasionally made mistakes about paternity, as we all do, paternity (and maternity) were important to them because they were associated with rights to land. These paternities are, of course, all taken from the Vikings’ written records, the sagas that were composed and/or written down mainly in the thirteenth century to provide records of individual family histories. As with all historical records, we might ask whether we can rely on them: after all, victors in history tend to colour the accounts they give with their particular view. There are, however, three relevant circumstances in this particular case. First, these accounts were written for public consumption by a very small community (medieval Iceland) where most people were intimately familiar with both the events and the characters described (in most cases, their own immediate ancestors): they would not have hesitated to say so if Snorri Sturlson (who was responsible for composing a great many of the Icelandic sagas in the 1220s and 1230s) had made too many egregious errors. Second, the Vikings themselves were very clear on real paternity (as best as they could define it biologically): despite the fact that fostering was a major feature of their world (as it continued to be into quite recent times throughout northern Europe), they made a clear distinction between foster-sons or foster-brothers and real sons or real brothers. Foster-sons could inherit land from a foster-parent if the parent so chose, but they did so by right of adoption and not by birth-right. Finally, even if the stories are complete fiction, we can still ask: did the Vikings compose their stories in such a way that they followed biological prescriptions…?

“Another example of the way biological kinship intrudes into everyday life is provided by Madsen et al. They asked individuals from two different cultures (the UK and South African Zulus) to undertake a painful isometric skiing exercise for the benefit of relatives (who received a monetary or food reward that was directly proportional to the length of time for which the exercise was maintained). In five replicates of the experiment, the duration (and hence reward value) declined with declining relatedness to the subject. In this study, considerable care was taken in drawing up lists of potential beneficiaries to ensure that they were biological relatives of the specified degree. While there was inevitably a great deal of variation across individuals, the bottom line is that, on average, closer relatives did better than more distant relatives (or even children’s charities) across four degrees of relatedness (self vs siblings/parents vs grandparents/uncles/aunts/nieces/nephews vs cousins). When real sacrifice is involved (the exercise becomes excruciatingly painful the longer one does it), altruism is titrated by genetic relatedness.”

what i find really interesting (obviously, if you’ve been reading this blog for any length of time!) is how inbreeding (and outbreeding) relates to inclusive fitness. sure, a brother might be really predisposed to help out his brother much more so than a distant cousin — but what if that brother is also a cousin? shouldn’t cousin-brothers, on average, be willing to help each other more than just regular brothers? the answer seems to be yes.

what should be kept in mind about inclusive fitness, though, is that there are other social behaviors that it probably affects in addition to altruistic ones. ever since bill hamilton published his ideas on inclusive fitness, most researchers have been focused on altruistic behaviors. but one of hamilton’s papers was entitled “The Innate Social Aptitudes of Man.” note, not the innate altruistic aptitudes of man — but the social aptitudes of man. hamilton obviously thought his idea applied to other behaviors as well in addition to altruism.

one of those other behaviors, i think, is a drive to exercise some control over who your relatives (i.e. other individuals who share YOUR genes) mate with. i haven’t seen much discussion of this amongst sociobiologists — i referred to one interesting study in my “nepotistic nosiness” post. there’s more of this going on, i’m sure — or i bet, anyway. people (and other organisms) want to control, to different extents, how their relatives pass on the genes which they share in common. and, like in the proven cases of altruistic behaviors, they probably want to exercise greater control over the reproductive practices over closer relatives. AND, where inbreeding occurs, there are probably even stronger drives to control the reproductive practices of relatives, e.g. all the reproductive controls in saudi arabia where the cousin marriage rates are currently 50%+.

just some thoughts.

(note: comments do not require an email. look! inclusive fitness.)



  1. You probably have seen this, but somebody went through all the backstabbing over the throne of England that Shakespeare dramatized in his history plays and, sure enough, it follows this same pattern: me and my brother against my cousin.


  2. @steve – i haven’t read it myself, but dunbar refers to it in the article i quoted from. must look it up!

    “me and my brother against my cousin.”

    i like the welsh version that i just learned today (in today’s post): “marry in the kin and fight the feud afar.” heh.


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