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!)

friendship and natural selection (and human biodiversity)

i linked to this paper…

Friendship and Natural Selection

…in this past sunday’s linkfest, but, to be honest with you, i hadn’t actually read it. (yeah, i do that sometimes. ok, ok — a LOT of times!)

since then, a couple of people urged me to read the arXiv blogpost on it (thanks @DKshad0w and @SamoBurja!), which prompted me to read the orig. research paper and … wow! … mind. blown.

now, no, i’m NOT a geneticist — i don’t even play one on the innerwebs — so i’m not your gal for evaluating whether or not these guys — nicholas christakis and james fowler — have done their work right, but if they have, this is very cool stuff:

Pairs of friends are, on average, as genetically similar to one another as fourth cousins, which seems noteworthy since this estimate is net of mean ancestry and background relatedness.”

fourth cousins! note that these are (i believe) all white folks. the data are from the framingham heart study, but the researchers do say that they controlled both for relatives (i.e. that individuals might be “friends” with people who are, in fact, distant relatives) and ethnicity (eg. that italians might just be friends with other italians).

It is intriguing that genetic structure in human populations may result not only from the formation of reproductive unions, but also from the formation of friendship unions. This in turn has relevance for the idea of an evocative gene-environment correlation, proposed more than 30 years ago, which suggests that a person’s genes can lead one to seek out circumstances that are compatible with one’s genotype. Our results suggest that these circumstances could include not only the physical environment but also the *social* environment, and hence the genotypic constitution of one’s friends. As Tooby and Cosmides argue, ‘not only do individual humans have different reproductive values that can be estimated based on various cues they manifest, but they also have different association values.’ People may seek out particular, convivial social environments that affect their fitness.

i’ve been saying for a while now that the family types/social structures in which individuals are located ought to be taken into consideration when thinking about the fitness of those individuals and how natural selection might be working on different individuals living and reproducing in different sorts of social structures (individuals living in nuclear family structures versus large clan structures, for instance). i’ve mostly been thinking about family structures, but christakis and fowler are talking about friendship structures — alliances with non-family members. cool!

“The existence of excess genetic similarity between friends is also relevant to the growing area of indirect genetic effects, wherein the phenotypic traits of focal individuals are influenced by the genomes of their neighbors, in a kind of ‘network epistasis.’ In fact, our results support the idea that humans might be seen as metagenomic not just with respect to the microbes within them, but also with respect to the humans around them. It may be useful to view a person’s genetic landscape as a summation of the genes within the individual and within the people surrounding the individual, just as in certain other organisms.

yeah. just muse on THAT for a while. (~_^) and then try this on for size…

“[T]he human evolutionary environment is not limited to the physical environment (sunshine, altitude) or biological environment (predators, pathogens), but also includes the social environment, which may itself be an evolutionary force. Our finding that positively correlated genotypes are under positive selection suggests that the genes of other people might modify the fitness advantages of one’s own genes, thus affecting the speed and outcome of evolution.

did you get that? the researchers found that, the SNPs that were most common between the friends (the homophilic SNPs), have, indeed, been under recent positive selection:

“To test the hypothesis that homophilic SNPs are generally under recent positive selection, we use the Composite of Multiple Signals (CMS) score. This score combines signals from several measures of positive selection to create a single value that indicates the likelihood a SNP has been increasing in frequency due to selection pressure over the last 30,000 years (see SI). In Fig.3, we show that, after correcting for correlated outcomes due to linkage disequilibrium and for varying precision in the GWAS estimates (see SI), the top 20% most homophilic SNPs have significantly higher CMS scores than the other 80% (+0.07, SE 0.02, p = 0.003)…. In contrast, Fig.3 also shows that CMS scores are not significantly higher for the most homophilic SNPs in the strangers GWAS (–0.00, SE 0.02, p = 0.86). This suggests that the whole-genome regression model we use does not generate false positives…. In sum, it appears that, overall, across the whole genome, the genotypes humans tend to share in common with their friends are more likely to be under recent natural selection than other genotypes.

friendship and natural selection 01

friendship and natural selection 02

with human biodiversity in mind, my question would be: do all peoples everywhere form an equal number of friendships with (technically) unrelated individuals? yes, i have an obsession with clannish peoples — but, seriously — do people who live in clans or tribes make as many “friends” as peoples who don’t? do they even have the opportunity? if not, what might this mean for natural selection in those populations?

(note: comments do not require an email. friends.)


in 1964, william d. hamilton published a couple of papers outlining his theory of inclusive fitness in which he suggested that individual organisms may increase their total fitness (i.e. the propogation of their genes) not only by reproducing themselves, but also by helping out other individuals with whom they share genes to reproduce successfully. if, in addition to having two children myself (or none at all for that matter), i also help my two siblings — with whom i share genes — to raise a couple of kids each, then i have helped to propogate even more copies of my own genes than those that my children carry. i have increased my fitness.

hamilton gave some examples in one of these papers of how this might work in various animal societies. he talked a lot about ants, for one, and how inclusive fitness explains the quirky social structure of the ant colony — i.e. that (in most ant societies) only the queen reproduces and all the rest of the ants just work to help raise her kids. why would any ant in their right mind do such a thing? well, the key is that, because of the way ants reproduce (don’t ask — it’s too complicated!), the worker ants actually share three-quarters (0.75) of their dna with their sisters rather than, say, one-half (like in humans), so it makes more sense for them fitness-wise to help raise their sisters than their own offspring. hamilton had cracked the mystery of the seemingly incomprehensible altruistic behaviors of ants.

much hilarity research into inclusive fitness and altruism has ensued since the publication of hamilton’s articles.

and while that’s all really interesting (really, really interesting!), hamilton thought that inclusive fitness could explain not just altruistic behaviors, but all sorts of social behaviors in organisms (including humans, of course), as is evidenced by the title of another one of his papers: “Innate Social Aptitudes of Man: an Approach from Evolutionary Genetics.” not the “innate altruistic aptitudes of man” but the “innate social aptitudes of man.” many different types of human behaviors hinge on inclusive fitness from the altruistic to the (depending on your p.o.v.) very un-altruistic.

one set of behaviors that seems to be influenced by inclusive fitness considerations is the control of reproduction in others. this has been fairly well established in certain social animals (mongooses, meerkats, naked mole-rats); but it also — not surprisingly — seems to be the case in humans. i haven’t discussed it much on the ol’ blog here, but i have brought it up once or twice. well, once anyways. humans — like mongooses, meerkats and naked mole-rats — take a keen interest in who their relatives choose to mate with — and they’re (we’re) more interested in the mating choices of closer relatives than more distant ones. this makes sense because we share more genes with more closely related relatives.

so, all sorts of social behaviors beyond altruistic ones are probably affected by inclusive fitness.

the other thing to keep in mind (which i’ve been babbling about at length here on the hbd chick blog) is that different populations of people have different degrees of relatedness to their fellows due to different mating patterns. this makes the inclusive fitness thing all the more interesting because, for instance, in many societies around the world, peoples’ children are also their cousins and so they (probably) share more genes with their children than we do with ours. therefore, their inclusive fitness interests in their children will be somewhat — or, perhaps, very — different from ours.

different degrees of relatedness (looking away from any inbreeding for a sec) have been shown to affect the behaviors of family members toward one another. the different types of grandmothers (paternal versus maternal), for instance, behave differently towards their male and female grandchildren because of inclusive fitness-related interests. (grandmothers are related to their granchildren to various degrees due to the differential inheritance of the sex chromosomes.) imagine what happens when inbreeding occurs and these different degrees of relatedness are, therefore, amplified.

mating patterns affect social behaviors right across entire societies because the relatedness between individuals in different societies differs. thus you get the rampant nepotism and clannishness in places like iraq and afghanistan that makes, as steve sailer, parapundit, stanley kurtz and robin fox have all pointed out, a political system based on democracy a non-starter in those places. the people in those populations are too genetically invested in their fellow family members to ever want to cooperate in a civil society with unrelated individuals. there is too much genetically at stake for them to do so.

the flip-side of inbreeding (too much?) is outbreeding (too much?). outbreeding results in a different set of inclusive fitness-related drives and issues as compared to inbreeding. in a population that is not inbred you get, as steve sailer put it, “broad but shallow regional blood ties.” inclusive fitness interests in an outbred population operate in such a way as to make, not the members of a clan (a very extended family) driven to cooperate against all outsiders like in an inbred society, but rather a much larger number of more distantly related individuals — a nation you might call it — really eager to work together. this is because the members’ genes are spread out over a wider population.

and, in a nice recursive twist, inclusive fitness and genetic relatedness affect the structures of societies — which, in turn, become new environments with new factors for natural selection to “use” upon individuals. a shift in mating patterns can mean a shift in the social environment, as we’ve seen in medieval europe (if you’ve been following along), which can mean that different behavioral traits will be selected for in a population. (yes, i know — i should read “A Farewell to Alms.”) what goes around comes around.

so, inclusive fitness underlies not only altruism and social control of reproduction, but nepotism and tribalism — and even individualism and democracy and universalism. genetic relatedness and inclusive fitness are the keystones of human social behaviors from the small (whether your favor your son or your daughter) to the great (western civilization as we know it). am i over-estimating its importance? maybe. but i don’t think so. it’s all biology, after all. (or maybe chemistry … or physics ….)

edit: boilerplate and boilerplate 2.0

see also: cousin marriage conundrum addendum and everything in the “Inbreeding in Europe Series” listed below in the left-hand column.

update 11/23/11: see also four things.

(note: comments do not require an email. altruism?)

setting the stage?

what if the degree/type of relatedness between the members of a society affects the selection pressures on those individuals?

what i’m thinking is: if my little hypothesis is correct that europeans quit being tribal because we started (and continued) outbreeding, what then? which individuals will do well (and succeed reproductively) in the new environment as opposed to the old?

the old, tribal social environment was one in which family/clan units were tightly knit and social stuff (like who gets to punish a lawbreaker, for instance) was based on the family/clans.

the new, corporate social environment is one in which clan units disappeared to be replaced with individuals/nuclear families as the basic units in society, and social stuff (like who gets to punish a lawbreaker) is based on the corporate groupings of a bunch of individuals (in the case of enforcing the law, the state).

so, who’s going to do well in such a society? what, for instance, personality traits might be selected for (or against, for that matter)? one possible example i thought of: might the “genes for” reciprocal altruism (whatever they might be) be more frequent in a corporate society than in a tribal one? makes sense to me. conversely, maybe the “genes for” altruism towards family members (whatever they might be) are more frequent in a tribal society.

just some thoughts.

previously: and so my next question naturally is…

(note: comments do not require an email. happy monday morning!)

and so my next question naturally is…

…what sort of selection pressures for, say, behavioral traits and iq existed under the manoralism system in medieval europe versus the earlier tribal system? (obviously these are pretty broad categories that changed in nature quite a bit over time and between places, but still….) i’m thinking along the lines of “The 10,000 Year Explosion” in which (duh!) human evolution is ongoing and, like in the case of ashkenazi jews in europe, what happened during the medieval period was obviously important.

so, what happened to the germanic peoples during the middle ages evolutionarily speaking? anything? nothing? a lot?

in a tribal system, you’d think that within any given clan or tribe, most or all of the members would be kinda-sorta taken care of since everyone is family. you’d think that a lot of the members, therefore, would be able to leave at least some descendants behind. obviously, the chief of a clan might be able to leave behind the mostest descendants of all, but might it be that in a tribal system, more of the members might be reproductively successful than maybe…

…in the manoralism system, where the extended family system is gone and we’re left with pretty much just nuclear families operating in a corporate sort of world. in the manor system, there were different classes of peasants/laborers from free tenants to slaves (again, depending on when and where you’re talking about). but, clearly, those more able to succeed under the manor system prolly left behind more descendants than some others (’cause they were more fit to that environment, no?). so, those able to work their way up to and maintain the status of peasant or free tenant presumably were the most successful reproductively (after the lords, of course).

given that these peasants had to work their own land as well as do a lot of work on the manor — and given that many of them settled and opened up new territories in eastern europe (in which to farm the new grains with the new techniques) — what traits might have served the successful ones well?

obviously, you couldn’t be too dumb. maybe even practical, 3-d rotation intelligence would be good to have for engineering drainage systems and the like. i’d say that personality traits like hard-working and industriousness would also be selected for. i guess that might sorta be conscientiousness in a way, but not exactly. law abiding? conformity? i.e. not rocking the manoralism boat too much?

i also think in this new, non-tribal corporate world, whatever “genes for reciprocal altruism” might exist would prolly be selected for at greater rates than in a tribal society ’cause in the latter, kin selection altruism should be enough to keep things ticking along amicably. but not in a society where people are not so closely related.

anything else? any of this sound completely far out?

previously: medieval manoralism and genetic relatedness and more on inbreeding in germanic tribes and loosening of genetic ties in europe started before christianity?

(note: comments do not require an email. the peasants are revolting!)

papa was a rolling stone

researchers have found that, in zebra finches, cheating on a partner (zebra finches are pretty monogamous usually) is an inherited trait.

from new scientist:

“Zebra finches form monogamous lifetime partnerships, but both males and females indulge in extramarital sex. The benefit for the males is clear: the chance to sire more offspring than fidelity would permit. But why would females cheat when that means risking losing their lifetime partners and catching diseases?

A new study suggests females are promiscuous simply because they inherit many of the same genes responsible for promiscuous behaviour in males.”

the researchers found that both male and female finches who had fathers that had “strayed” were more likely to engage in extrapair copulations themselves. this was the case even when daddy was not around to raise them, so they couldn’t learn the behavior through watching him (the researchers were very sneaky and shuffled eggs between nests!).

from the research article:

“Here we show that in the socially monogamous zebra finch, individual differences in extrapair mating behavior have a hereditary component. Intriguingly, this genetic basis is shared between the sexes, as shown by a strong genetic correlation between male and female measurements of extrapair mating behavior. Hence, positive selection on males to sire extrapair young will lead to increased extrapair mating by females as a correlated evolutionary response. This behavior leads to a fundamentally different view of female extrapair mating: it may exist even if females obtain no net benefit from it, simply because the corresponding alleles were positively selected in the male ancestors.

and more:

“In humans, individual differences in attachment style, fidelity, and sociosexuality are known to have a hereditary basis. The degree to which variation in physiological mechanisms of attachment and of sexual arousal is shared between the sexes is not sufficiently known to predict whether between-sex correlations [like in the finches] can be expected. At the phenotypic level, sexual fidelity correlates with several of the major axes of personality variation (extraversion, agreeableness, and conscientiousness) and, importantly, these correlations are largely consistent between the sexes. The apparent multitude of aspects of personality that may influence sexual fidelity is in agreement with the hypothesis of Halliday and Arnold: such a genetically complex trait would represent a large target for new mutations that would typically have similar (correlated) effects on both sexes.”

in other words, a similar pattern of selection for “infidelity genes” might also be the case in humans (not to mention other animals). maybe.

so, just to be safe, if you’re looking for a mate who will remain faithful, find out how faithful their father was. (especially if you’re a zebra finch.)

(note: comments do not require an email. and i don’t mind if you read other chick blogs, either. no really i don’t. *sniff*)