inclusive inclusive fitness

inclusive fitness means you can increase your own (genes’) fitness by somehow being altruistic to other individuals out there who share your genes, family members being the most obvious choice (’cause they typically share a lot of your genes — especially if you’re a bee). an altruistic behavior is defined in biology as some action which helps out another individual(s) while costing the altruistic individual a chance at reproducing or even surviving.

let’s take my example from my last post on altruism: the suicide bomber. the suicide bomber makes the ultimate sacrifice — 100% of his genes on behalf of, presumably, some or all of his extended family members. here he is — mr. light-blue square. by blowing himself up — and possibly taking some of his family’s enemies’ genes with him — he forfeits all of his genes, outlined in red, that are found in his own genome:

but, there are other copies of his genes in other people — that’s kinda the whole point.

now, remember mr. light blue and miss light pink from this post? well, here they are again. they’re first-cousins so (barring any other inbreeding) they prolly share 1/8th of their genes in common, thus they overlap:

and here, they’ve mated and had a daughter, miss deep-pink, who has inherited half of her father’s chromosomes and half of her mother’s, but she’s gotten some duplicate copies of genes (alleles) because her parents shared genes (alleles) in common (i.e. where they overlapped). (like her brother, mr. deep-blue, she’s “less of an individual” than an outbred person.):

i’ve purposefully picked first-cousin marriage here because i want to take a look at another example of altruism from the muslim world — honor killing (i know — honor killings are not restricted to muslim societies).

what happens genetically when a parent — or often parents — kills one of his kids?

well, in the suicide bombing example above, the individual sacrificed 100% of his genes for his family. in the case of honor killing, he sacrifices half of his genes for his family plus the extra copies of his genes/alleles that his daughter carries due to the inbreeding — according to my calculations, that means he’s sacrificing (prolly) 56.84% of his genes (in an fbd marriage scenario, which is a typical cousin-marriage pattern found in the muslim world). (all of this can be flipped around to view it from the mother’s p.o.v., obviously.) here again, outlined in red, are the genes that he altruistically sacrifices.:

it doesn’t really matter if he sacrifices his genes within his own genome or his genes within his daughter’s genomeeither way, he’s still sacrificing some of his own genes for a greater number of his own genes found in other individuals.

and 56.84% vs. 100%? — honor killing is clearly an altruistic bargain compared to suicide bombing. =/

also, in the honor killing situation, dad’s still around to live another day and possibly even reproduce some more. still, it is something to sacrifice the young who probably have before them more opportunities to reproduce than dear old dad. they are the future, obviously. (i’ve read somewhere that honor killings often or typically take place when whatever the scandal is becomes publically known — otherwise, of course, a family will try to cover things up. why sacrifice a family member if you don’t have to? unfortunately, can’t find the reference where i read that. pretty sure it was daniel pipes.)

but who is benefitting from this altruistic killing? well, westerners often belittle the claims that muslims and other peoples make when they say that they’re saving their familiy’s honor in murdering a daughter (or two or three) — but if your other children are unable to marry** because of one child’s bad behavior, then obviously honor killing becomes an altruistic act, since in total you will benefit a greater number of your genes by sacrificing some of them. that’s the biological definition of altruism.

honor killings are really an example of inclusive inclusive fitness since the altruistic individual’s genes that are sacrificed on behalf of copies of his genes in other individuals are other copies of his genes in other individuals. (got that?)

the long history of inbreeding in middle eastern/north african/south asian muslim societies is important here, too, ’cause remember — inbreeding means that the evolution of altruism in a population is made easier. whatever genes that influence the willingness, for ultimately altruistic reasons, to kill an offspring, a pretty extreme step — genes that make individuals within these societies, on average, more willing to do it than otherwise — seem to have arisen and flourished in these populations, undoubtedly because of their particular evolutionary history.

no, of course i’m not condoning honor killings — or any other kind of killing for that matter (self-defense is ok). i’m only trying to explain them. by understanding where the drive for them comes from, maybe people can put an end to them (if they want to).

**remember how in “Pride and Prejudice,” miss elizabeth bennett fretted that that she and her other sisters would have difficulties marrying because of the disgrace lydia brought on the family…?

previously: which altruism genes?

(note: comments do not require an email. can’t think of anything funny to say about honor killings. =/ )



  1. Excellent analysis. Thank you. I plan to quote you in a book I’m now finishing up: Hbd* chick makes a compelling argument that honor killings count as an important example of inclusive inclusive fitness because “… the altruistic individual’s genes that are sacrificed on behalf of copies of his genes in other individuals are other copies of his genes in other individuals.” But this act becomes biologically altruistic only because, in this form of an honor culture, surviving children may not be able to marry.


  2. @docpenn – “Thank you. I plan to quote you in a book I’m now finishing up….”

    well, thank you! glad you found this useful. let me know what the book is and when it’s been published! (^_^)


  3. […] behalf of a person, for his blood relatives, should increase in frequency through selection [see inclusive inclusive fitness | hbd* chick]. This is especially the case for populations that have been inbreeding throughout the ages — […]


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