inclusive fitness

there’s some amount of confusion out there in the hbd-o-sphere (and beyond!) about inclusive fitness, which is understandable since the concept is not that straightforward — especially for those of us who are not scientists. i thought it’d try to dispel some of that misunderstanding by sharing my layman’s understanding of the concept — i think i grok the idea pretty well now (in a basic sorta way) — hope i don’t add to the confusion!

to start with, inclusive fitness is NOT some sort of biological law that organisms (including humans) will automatically be altruistic towards other individuals with whom they share a lot of genes (or vice versa if vice versa). if you hold that idea — and i get the impression that a lot of people do — get it out of your mind right now! you’ll feel better for it, trust me.

inclusive fitness is simply a concept or model which explains HOW certain social behaviors — especially altruism — might’ve evolved at all. period. full stop.

to understand inclusive fitness, we need to back up a sec first and think about fitness and what that is. very (very!) simply, fitness refers to an organism’s ability to survive and reproduce in a particular environment. traits — including behaviors — that enable an organism to survive and successfully reproduce will be selected for simply because that organism *is* able to survive and reproduce in its environment. this is natural selection. pretty simple, really, darwin’s dangerous idea.

when it comes to certain social behaviors in humans, it’s readily understandable why many of them were selected for. for example, mothers who devote a lot of time and energy to care for their infants — who obviously can’t take care of themselves and would die without any care — will be more fit than those mothers who don’t. the genes that predispose for those behaviors get selected for since children get half of their dna from their mothers, and the ones that are cared for are much more likely to survive.

what was — and to some extent still is — a big mystery is why other sorts of altruistic behaviors were ever selected for even though they hurt an organism’s fitness. how would self-sacrificing altruistic behaviors directed towards non-descendants ever be selected for? for instance, why on earth would somebody feel compelled to run into a burning building to save a neighbor (who wasn’t their child) at great risk to their survival and, therefore, to their fitness? we can see how “genes for altruistic behaviors towards offspring” could be passed down from mother (or parents) to kids, but how were genes for more general altruistic behaviors selected for?

here is where william hamilton‘s absolutely genius idea — inclusive fitness — comes in: perhaps certain social behaviors, which on the surface appear to reduce an organism’s fitness, and so shouldn’t get selected, might’ve been selected for if those behaviors were directed toward other close kin with whom individuals also share much dna in common.

everybody gets half of their dna from each of their two (for now, anyway) parents. but we also share dna with siblings and (blood-related) aunts and uncles and (wait for it…) cousins. given this inheritance pattern, probability says, for instance, that, in a randomly mating population, an individual should share 12.5% of their dna with a first cousin. so, if an individual with certain “genes for altruism” behaves altruistically toward their first cousins, odds are not bad that those first cousins might also have those same “genes for altruism.” here, then, we have a mechanism for how apparently self-sacrificing social behaviors can be selected for: since the altruistic individual 1) aids close kin with whom he shares much of his dna AND 2) probably in many instances shares the same “genes for altruism,” his being altruistic toward those kin 1) does not reduce his fitness AND 2) the “genes for altruism” get selected for, too. mystery solved. (see also: kin selection.)

one way i like to think of inclusive fitness — which, perhaps, isn’t entirely the right way to look at it, but i feel it helps my understanding — is that if you wanted to calculate an individual’s total fitness by adding up how many actual copies of his genes he passed on, you need to add together those found in his offspring and those in his close relatives’ offspring. in other words, you need to add together his own direct fitness plus his close relatives’ fitness to get his inclusive fitness (or his total fitness).

it seems likely that many of the altruistic (or spiteful, etc.) behaviors we’re talking about are pretty general in nature, i.e. not that specific behaviors like “be altruistic to your close kin” were selected for, but rather more like “be altruistic to the people around you, because they’re probably your close kin” were. it remains to be seen how much kin recognition plays a role in altruism in humans, but that’s a topic for another post anyway. for right now, i just wanted to make clear what inclusive fitness is — and isn’t. again, inclusive fitness is a concept which explains HOW altruistic behaviors MIGHT be selected for. it does NOT predict that individuals will DEFINITELY be more altruistic toward those with whom they share much dna.

the whole topic of inclusive fitness is, of course, much more complicated than all that, but i think this is a good basic intro to the concept. hope so, anyway! (^_^)

(note: comments do not require an email. citizens against altruism!)

recognizing your un-kin

if you want to be un-altruistic toward some un-kin of yours, it might be useful if you could spot who they are.

here’s some neat research [pdf] suggesting that perhaps we can do just that (further research is required, of course). this is one of those manipulated photographs studies — you know — where they take photos and alter them to look more or less like the subjects. note that the study was done on w.e.i.r.d. students — and way more females (n=112) than males (n=32):

“Kin recognition: evidence that humans can perceive both positive and negative relatedness” (2012)

“… The evolution of spite would have been greatly facilitated by the ability to recognize negative relatives (West & Gardner, 2010). The current study is the first to find such an ability among humans, one of only a handful of species (Keller & Ross, 1998; Giron & Strand, 2004) for which there is evidence of negative relatedness recognition, by introducing a novel cue to negative relatedness (negative self-resemblance). Specifically, we found opposing effects of positive and negative self-resemblance – cues to positive and negative relatedness, respectively – on trusting and attractiveness attributions, as predicted. This result provides a foothold for the possibility of the evolution of spiteful behaviour among humans. Future research should examine this possibility.

“Although the effects of positive and negative self resemblance in our study were generally small, our study was an experimental one. Thus, we controlled the strength of the manipulation. It was our intention to make the stimuli subtle, to ensure that the participants would not discover the nature of the manipulation. A subtle manipulation, however, will tend to lead to subtle effects. What we hoped to show was not that the positive and negative self-resemblance manipulations had large effects on preferences or behaviour in the context of a laboratory experiment, but that they had predictable effects at all, especially as these effects speak to theory (Prentice & Miller, 1992).

Relative to matched participants, focal participants generally had positive preferences for their own positive self-resembling faces but negative preferences for their own negative self-resembling faces across contexts….

here’s the relevant graphic:

negative relatives

Spite is hypothesized to evolve under relatively restrictive conditions (West & Gardner, 2010), and so it is expected to be rare. However, two conditions may, together, favour its evolution: (1) ‘viscous’ breeding systems and (2) the ability to recognize negative relatives. Population viscosity can make competition increasingly local among individuals (Taylor, 1992a,b), and local competition encourages the evolution of spite (Gardner & West, 2004). Furthermore, individuals immigrating into a viscous population may be strongly negatively related to members of the indigenous population, because immigrants are highly unlikely to bear the same (relevant) alleles as indigenous individuals (Krupp et al., 2011).”

for “viscous breeding systems” i think we can safely insert “inbreeding” or “cousin marriage” or “consanguineous matings.” they are all certainly viscous.

“Negative relatedness recognition can improve the targeting of a spiteful action to increase indirect fitness benefits (by delivering harm specifically to negative relatives whilst sparing positive ones), and our results provide evidence that humans have the mechanisms in place to do precisely this. Moreover, countless animal species use phenotype matching to determine relatedness, and other kin recognition systems exist that might also be employed to discriminate against negative relatives (reviewed in Krupp et al., 2011). Further discoveries that organisms have the capacity to recognize negative relatives will lay a foundation for the study of spiteful behaviour, arguably the last great unexplored problem of social evolution….”
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what i’d like to see is some research done on actual inbred populations. maybe a comparison between a non-inbreeding population and an inbreeding one to see if either of the two groups is better at spotting their kin or un-kin.

for that matter, i wonder if kin in inbred populations actually look more like one another than kin in outbred populations (and, therefore, look more unlike non-kin). you would think they ought to since they share more of the same genes with one another. you’d think that’d affect appearance, too. remember the ghoul brothers from syria (click on picture for LARGER view)?:

ghoul brothers

redzengenoist said about them: “It really is striking how much they look like one another. Far more than I would expect the average family group to have similar appearance…. I’m thinking of selection for markedness of ingroup-ness. I can’t help but wonder if having a distinct ‘look’ helps to facilitate the evolutionary advantages of inbreeding….”

i noted: “and, like the big families i’ve known (from my slightly inbred area of the world), some of them look more like each other than they do to the others. the two (chubby guys, roundish faces) on the right and the guy all the way on the left look similar — those three look like mom? or dad? and the other five look more like each other — like the other parent (whichever one).”

maybe it’s easier to spot kin and non-kin in a “viscous” population. the more viscous the better, perhaps.

(note: comments do not require an email. play spot the relatives!)