Relatedness is relative: How can I be 85% genetically similar to my mom, but only related to her by half?

First of all, no. I am not the lovechild of star-crossed siblings, or even cousins, or even second cousins. 

This is a gee-whiz kind of post. But the issues are not insignificant.

Hear me out with the background, first, before I get to the part where my eyes bug out of my head and I pull out my kid's Crayola box and start drawing.

If you've learned about sociobiology, or evolutionary psychology, or inclusive fitness, or kin selection, or the evolution of cooperation and even "altruism," or if you've read The Selfish Gene, or if you've been able to follow the debate about levels of selection (which you can peek at here)...

... then you've heard that you're related to your parents by 1/2, to your siblings by 1/2 as well, to your grandparents and grandchildren by 1/4, to your aunts and uncles and nieces and nephews by 1/4 as well, and to your first cousins by 1/8 and so on and so forth.  (Here's some more information.)

So, for example. For evolution (read: adaptationism) to explain how cooperative social behavior could be adaptive in the genetic sense, we use the following logic provided by Bill Hamilton, which became known as "Hamilton's Rule": 

The cost to your cooperation or your prosocial behavior (C) must be less than its benefit to you (B), reproductively speaking, relative to how genetically related (r) you are to the individual with whom you're cooperating. That could have come out smoother. Oh, here you go:

C < rB, or B > C/r

If you're helping out your identical genetic twin (r=1.0), then as long as the benefit to you is greater than the cost, it's adaptive.

C < B, or B > C

If you're helping out your daughter (r = 0.5) then as long as the benefit to you is greater than twice the cost, it's adaptive.

C < (1/2)B, or B > 2C

So already, the adaptive risk to helping out your daughter or your brother is quite higher. And it's even harder to justify the cooperation between individuals and their sibs' kids, and grandkids, especially ESPECIALLY non-kin. But, of course creatures do it! And so do we.

As relatedness gets more distant and distant, we go from 2 times the cost, to 4 times, 8 times, 16, 32, 64 etc... You can see why people like to say "the math falls away" or "drops off" at first or second cousins when they're explaining where the arbitrary line of genetic "kin" is drawn.  If you offer up a curious, "we're all related, we're all kin," someone out of this school of thought that's focused on explaining the evolution of and genes for social behavior may clue you in by circumscribing "kin" as the members of a group that are r = 1/8 or r = 1/16 but usually not less related than that.

This has long bothered me because we're all genetically related and so much cooperation beyond close kin is happening. And it's been hard for me, as someone who sees everything as connected, to read text after text supporting "kin selection" and "kin recognition" (knowing who to be kind to and who to avoid bleeping), to get past the fact that we're arbitrarily deciding what is "kin" and it seems to be for convenience. I'm not doubting that cooperation is important for evolutionary reasons. Quite the contrary! It's just that why is there so much math, based in so many potentially unnecessary assumptions about genes for behavior, gracing so many pages of scientific literature for explaining it or underscoring its importance? 

(It could just be that as an outsider and a non-expert I just don't understand enough of it and if I only did, I wouldn't be gracing this blog with my questions. But let's get back to my reason for posting anyway because it's potentially useful.)

Right. So. Even for folks who aren't part of evolution's academic endeavor, it's obvious to most that we're one half dad and one half mom. The sperm carries one half of a genome, the egg another, and together they make a whole genome which becomes the kid. Voila!

There's even an adorable "Biologist's Mother's Day" song about how we've got half our moms' genome... 

... but there's biology above and beyond the genes we get from mom (and not from dad). And that song is great for teaching us that the rest of the egg and the gestational experience in utero provide so much more to the development of the soon-to-be new human. So "slightly more than half of everything" is thanks to our mothers. Aw!

But, genetically, the mainstream idea is still that we're 50% our mom. 

I teach very basic genetics because I teach evolution and anthropology.And I'm not (usually) a dummy.* I get it. It's a fact! I'm half, genetically, my mom and I'm also half my dad. 

r = 0.5

Okay! But, given these facts about relatedness and how it's imagined in evolutionary biology, facts that I never ever questioned, I hope you can see why this report from 23andMe (personal genomics enterprise) blew my mind:

Percent similarity to Holly Dunsworth over 536070 SNPs (single nucleotide polymorphisms or, effectively/rather, a subset of known variants in the genome; Click on the image to enlarge).
I am 85% like my mom and I am at least 76% like my students and friends who are sharing with me on 23andMe. Names of comparisons have been redacted. As far as I know, this kind of report is no longer offered by 23andMe. I spat back in 2011/12 and the platform has evolved since.

Okay, first of all, it is a huge relief that, of all the people I'm sharing with on 23andMe, the one who squeezed me out of her body is the most genetically similar to me. Science works.

But that number there, with my mother, it is not 50%. It's quite a bit bigger than that. It says I'm over 85% the same as her.

What's more, I am also very similar to every single person I'm sharing with on the site, including example accounts from halfway around the world. Everyone is at least 60-ish% genetically similar to me, according to 23andMe. I know we're all "cousins," but my actual cousins are supposed to be 1/8th according to evolutionary biology. How can my mom be related to me by only one half? How can my actual cousins be only an eighth (which is 12.5%)? 

What is up with evolutionary biology and this whole "r" thing?

Hi. Here is where, if they weren't already, people just got really annoyed with me. Evolutionary biology's "relatedness" or "r" is not the same as genetic similarity like that reported by 23andMe.

Okay!

But why not? 

Let me help unpack the 85% genetic similarity with my mom. Remember, it's not because I'm inbred (which you have to take my word for, but notice that most everyone on there is over 70% genetically similar to me so...).

It's because my mom and dad, just like any two humans, share a lot in common genetically. Some of the alleles that I inherited from my dad are alleles that my mom inherited from her parents. So, not only is everything I got from her (50%) similar to her, but so are many of the parts that I got from my dad. 

Let me get out my kid's arts supplies.

Here is a pretty common view of relatedness, genetically. In our imagination, parents are not related (r = 0) which can lead our imagination to think that their alleles are distinct. Here there are four distinct alleles/variants that could be passed onto offspring, with each offspring only getting one from mom and one from dad. In this case, the sperm carrying the orange variant and the egg with the blue variant made the baby.

1. (Please, if you're horrified by the "r" business in these figures, read the post for explanation.)

But few genes have four known alleles, at least not four that exist at an appreciable frequency. Some could have three. What does that look like? 

The green allele doesn't exist in the next example. As a result of there being only three variants for this gene or locus, mom and dad must share at least one allele, minimum. That means, they look related and that means that, depending on which egg and sperm make the kid, the kid could be more related to mom than to dad. 

2. (Please, if you're horrified by the "r" business in these figures, read the post for explanation.)

Now here's where people who know more than I do about these things say that the kid is not more related to mom than dad because she got only one allele from mom and that keeps her at r = 0.5. 

Well, that's just insane. What does it matter whether she got the allele from mom or dad? I thought genes were selfish? (Sorry, for the outburst.)

Again, I realize I'm annoying people and probably much worse--like stomping all over theory and knowledge and science--by mixing up the different concepts of genetic similarity (e.g. 50%) with "r" (e.g. 0.5) and horribly misunderstanding all the nuance (and debate) about "r," but I'm doing it because I'm desperately trying to know why these two related ideas are, in fact, distinct. 

One last pathetic cartoon. 

In this third example, as is common in the genome, there are only two alleles/variants in existence (at an appreciable frequency, so not accounting for constant accumulation of de novo variation). An example of such a gene with only two known alleles is the "earwax gene" ABCC11 (there's a wet/waxy allele and dry/crumbly one). Here, the two alleles are orange and blue. Most humans in the species will have at least one allele in common with their mate for a gene with two alleles, and it's not because most humans are inbred, unless we want to redefine inbreeding to include very distant relatives (aside: which may be how the term is used by experts). 

3. (Please, if you're horrified by the "r" business in these figures, read the post for explanation.)

But as a result of the chance segregation of either the blue or orange allele into each of the gametes, two people with the same genotype can make a kid with the same genotype. 

And of course, making a kid with your same genotype is the only possible outcome if you and your mate are both homozygous (i.e. where both copies are of the same variant so that leaves no chance for variation in offspring unless there is a new mutation). 

So, I wandered a little bit away from my point with these drawings, but I had to because I wanted to get down from where my imagination has me (us?) with "r" versus how things really are with reproduction. We are baby-making with vastly similar genomes to ours, so we are making babies with vastly similar genomes to ours. 

So, I do see why biology says I'm related to my mom by one half. But, on the other hand, what does it matter if I got the thing I have in common with my mom from my mom or whether I got it from my dad? Because I got it. Period. It lives. Period. 

[Inserted graf January 20, '17] Saying it matters where I got the similarity to my mom keeps us at r = 0.5. Saying it matters only that I inherited DNA like hers keeps us always, all of us, at r > 0.5 with our parents and our kids because any two babymakers share much of their genome.

And the fact that this (see 2 and 3) happens so often is why I'm a lot more than 50% genetically like my mom, and the same can be said about my genetic similarity to my dad without him even spitting for 23andMe. 

So, here we are. I don't understand why our relatedness to one another, based on genetic similarity, is not "r."

I hope it's for really beautifully logical reasons and not something political. 

Because...

If "r" was defined by genetic similarity, then would cooperating with my 76% genetically similar students and friends be more adaptive than the credit I currently get from evolutionary biology for cooperating with my own flesh and blood son? 

If "r" was defined by genetic similarity, then could we use the power of math and theoretical biology to encourage broader cooperation among humans beyond their close kin? 

So many questions.

Maybe I should re-learn the math and learn all the other math.

Nah. Not myself. At least, it wouldn't come fast enough for my appetite. Maybe someone who already knows the math could leave a comment and we could go from there... 

And it would be worth it, you know, because despite my relatively weaker math skills, I bet we're more than 50% genetically similar.

*from 23andMe: "You have 321 Neanderthal variants. You have more Neanderthal variants than 96% of 23andMe customers."

Seasonality of cooperative behavior in a large population of juvenile primates

My Grandpa used to read this on Christmas Eve, and most years we keep up the tradition.  It's an important first-person ethnographic account of the adaptive cooperative behavior displayed seasonally by many juveniles of our species. Enjoy...


Jest 'Fore Christmas
by Eugene Field (1850-1895)

FATHER calls me William, sister calls me Will,
Mother calls me Willie but the fellers call me Bill!
Mighty glad I ain't a girl---ruther be a boy,
Without them sashes curls an' things that's worn by Fauntleroy!
Love to chawnk green apples an' go swimmin' in the lake--
Hate to take the castor-ile they give for belly-ache!
'Most all the time, the whole year round, there ain't no flies on me,
But jest'fore Christmas I'm as good as I kin be!

Got a yeller dog named Sport, sick him on the cat.
First thing she knows she doesn't know where she is at!
Got a clipper sled, an' when us kids goes out to slide,
'Long comes the grocery cart, an' we all hook a ride!
But sometimes when the grocery man is worrited an' cross,
He reaches at us with his whip, an' larrups up his hoss,
An' then I laff an' holler, "Oh, ye never teched me!"
But jest'fore Christmas I'm as good as I kin be!

Gran'ma says she hopes that when I git to be a man,
I'll be a missionarer like her oldest brother, Dan,
As was et up by the cannibals that live in Ceylon's Isle,
Where every prospeck pleases, an' only man is vile!
But gran'ma she has never been to see a Wild West show,
Nor read the life of Daniel Boone, or else I guess she'd know
That Buff'lo Bill an' cowboys is good enough for me!
Excep' jest 'fore Christmas, when I'm as good as I kin be!

And then old Sport he hangs around, so solemn-like an' still,
His eyes they seem a-sayin': "What's the matter, little Bill?"
The old cat sneaks down off her perch an' wonders what's become
Of them two enemies of hern that used to make things hum!
But I am so perlite an' tend so earnestly to biz,
That mother says to father: "How improved our Willie is!"
But father, havin' been a boy hisself, suspicions me
When, jest 'fore Christmas, I'm as good as I kin be!

For Christmas, with its lots an' lots of candies, cakes an' toys,
Was made, they say, for proper kids an' not for naughty boys;
So wash yer face an' bresh yer hair, an' mind yer p's and q's,
And don't bust out yer pantaloons, and don't wear out yer shoes;
Say "Yessum" to the ladies, and "Yessur" to the men,
An' when they's company, don'a pass yer plate for pie again;
But, thinkin' of the things yer'd like to see upon that tree,
Jest 'fore Christmas be as good as yer kin be!

**

Season's greetings 

to you and yours from me and mine...

As good as kin be.
(Photo by Juliet Dunsworth)

Rhododendron walks into a bar...

By Anne Buchanan and Ken Weiss

Plants may be stuck in one place, but they aren't just sitting there twiddling their thumbs.  That they respond to environmental cues has long been known, of course, and the hormonal and molecular mechanisms for responding to light, temperature, moisture and so forth are well-established.  Some responses evoked by one part of a plant, such as attack by predator, can communicate to other parts or even to nearby plants.  But it has only fairly recently been suggested that plants are also able to recognize kin, and respond differentially, and in ways that enhance reproductive fitness, to the presence of plants to which they are closely related.

Among other reported indications of kin recognition, plant roots have been found to grow more in the presence of 'strangers' than 'kin'; kin recognition is said to be via root-derived cues, though that this actually happens is not without controversy, primarily because the molecular mechanism has not been identified (from 'Shedding light on kin recognition response in plants,' New Phytologist, Bias, 26 Nov 2014).  But now a new paper ('Photoreceptor kin-recognition among plants,' New Phytologist, Crepy and Casal, 29 Sept 2014) describes a possible mechanism for kin recognition among Arabidopsis thaliana, or mustard weed, the most frequently studied model plant.

Crepy and Casal did a series of experiments growing Arabidopsis plants in pots, to eliminate the possibility of confounding cross-talk between root systems, in variations on the theme of single genotype or mixed genotype rows, with plants either surrounded by kin or non-kin.  They also included mutant plants with known responses to different light waves, and plants of different ages, all exposed to differently filtered light sources.  They were interested in whether there were effects of proximity to kin, which they measured in terms of how close leaves were to neighboring leaves, or how much light fell on each leaf.  The idea was that kin don't compete over pools of light, but instead allow their relatives equal access.

Bias writes:

Crepy and Casal showed that plants recognized their kin neighbors by horizontally reorienting leaf growth compared with the interactions with the nonkin members. The authors also showed that the mechanism that led to reorientation of the leaf with kin members was regulated by phytochrome B and cryptochrome 1. The work by Crepy and Casal provides the first molecular evidence of the way in which plants respond to kinship.

They also showed that plants that interacted with kin produced more seeds than plants growing among strangers, "a clear indication of mutual benefit and cooperation."

From Bias, 2014;
'Aboveground and belowground interactions in plants experiencing kin and nonkin members.'

Have Crepy and Casal demonstrated beyond doubt that plants recognize kin?  Probably not; it has been controversial, and will surely remain so.  For one thing, there needs to be a convincing mechanism for recognizing what 'kin' means, and this is a serious issue both practically and theoretically.  In animals, with their various pheromones and highly variable immune/identity systems, the latter of which can be highly variable because mutations accumulate rapidly, various receptors and detection systems, also part of the system whose function is in mating or immune defenses, recognition of close molecular similarity in these aspects of the genome would be called 'kin'.   Plants also have high-variability immune-like systems for detecting invaders but whether they monitor this for self or self-like patterns is something we, at least, don't know.

It will take much beyond this rather limited study before any serious evolutionary geneticist will be completely convinced.  This is, in part, because authors must show beyond a reasonable doubt a molecular means specific enough to detect and evaluate the degree of kinship rather than just same-species or locally same-environment, both of which could affect many aspects of plant molecular biology.  Can a plant tell a clone from a cousin, say?  Finding such evidence has proven generally to be a very tall order, but of course that doesn't mean the Crepy and Casal finding is wrong, but it does need to be viewed with circumspection until details are known, because empirical findings like theirs can have multiple explanations.  The reason is not hard to see, and it seems there are some semantics involved, with the meaning of the term 'kin'.

The basic idea and rationale of kin selection
The main underlying idea that makes this of any interest has to do with altruism.  Helping any other organism may be at your own expense, and put you at a reproductive (and hence evolutionary) disadvantage if, say, it costs energy to help the recipient gain resources that lead to its greater reproduction when you could be putting that energy toward your own reproduction.  If that's the case, the genetic variants that lead you to do this won't proliferate as much as the recipient's. The explanation offered mathematically by William Hamilton over a half-century ago was that if your aid to a relative of a given degree -- and this is where 'kin' comes in -- must lead the recipient to reproduce more by a factor at least as great as your direct kinship relationship in order for the behavior to evolve.  In animal terms, you share half your genome with your sibling.  If you lose an offspring because you helped your sib, s/he must produce more than 2 additional offspring as a result of the help -- that is, in the next generation (on average) there will be at least as many copies of the altruism-inducing variant. If the recipient is of a more distant degree of relationship, the advantage must be much greater than just 2 for 1. 

Hamilton's rule was for decades a kind of cult religion among strong evolutionary determinists looking for precise natural selection everywhere.  To be fair, it also was a response to accounting for the evolution of what seemed like self-defeating behavior, to counter a heretical argument that invoked 'group selection', that organisms could evolve behavior that was self-limiting if it was good for the group.  This was heresy in the sense that it went against the rugged individualism of arch-Darwinism -- and mathematical analysis showed that was a more problematic phenomenon to account for.

However, careful quantitative ecological genetic studies have generally not supported the idea as of much practical applicability except in unusual circumstances.  On the other hand, in general if you help another member of your species, relative to other species, or if because you drop your seeds near where you live, your neighbors are  your relatives, then such behavior is easier to understand and doesn't require great precision -- for example, you don't have to have a mechanism for genotyping your neighbor, as you effectively do under Hamilton's rule.  If your neighbors are your relatives, helping is OK, and this can be so even if it's just within species if you are (or your ancestors at the time the helping mechanism evolved were) locally reproducing.

Likewise, if you compete for soil nutrients or sunshine with other plants where you live, it can in principle at least (this needs to be shown quantitatively) mean that you're better off by helping your species members rather than some other species.  Again, in the Hamilton's rule sense they share your genes far more than other species do.  These sorts of things can in principle account for the kin-recognition in plants that this paper refers to: it does not have to be testably close kin.


In this case, we think that the Crepy and Casal idea seems to have rather misleadingly used the term 'kin', not to refer to close family relationship of known degree but to what amounts to more distant group relationship.  Distant groups should not be referred to as 'kin' in this kind of situation because its connotation can be unclear.  After some variation has accumulated, it is clearly reasonable to ask whether similar molecular physiology might induce similar responses, or cross-reactivity, in those from the same group compared to those from a distant group.  No evolutionary kin-rule selection of the precise Hamiltonian kind need be involved.  In the wild, ancestrally, neighbors are kin.  In this case, if the story holds up, one will want to know how these particular genes effect such cross-reactivity.

Is it a perfect good?
But let's say that Crepy and Casal have demonstrated that plants help their kin.  And that kin recognition is an unalloyed good, with demonstrable fitness benefits.  As they point out,

Preferential helping of relatives has been observed for a wide range of taxa. For instance, in vertebrate (bird, mammal) species, helpers preferentially aid closer relatives during breeding (Griffin and West, 2003). In the social amoebae Dictyostelium discoideum, cells cooperate preferentially with relatives and aggregate to form multicellular fruiting bodies (Hirose et al., 2011). In humans, as the cost of helping increases, the share of help given to kin increases, whereas that given to nonkin decreases (Stewart-Williams, 2007).

The assumption is that the more closely related organisms are, the more likely they are to cooperate.  That is, increasing the reproductive fitness of one's kin is good for one's own fitness.  The reason that kin selection has been, and continues to be a hot topic in human evolution is both that it confirms hyper-darwinian fine-tuned selection, which many hold as fervently as a religion, and that it accounts for cooperation without being culturally wishy-washy (as they'd see it), and that there should be a mechanism to account for its evolution; note of course, that mechanism needs to be quite specific to define 'kin', which cannot just be assumed (as we outlined in the previous section).  But we, at least, have plausible molecular-genetic means of detecting close kin.

But people aren't plants, or dictyostelium.  We also have culture, and it can powerfully affect our behavior, so that what makes sense evolutionarily for other organisms doesn't always apply to us.   For one thing, culture allows us to assign relationships symbolically rather than just genetically.  We can imagine what 'success' may mean (e.g., getting to heaven), which goes beyond mere Darwinian proliferation.  We can form clans or other structures based on all sorts of criteria, not just genetic relationships. We don't always optimize our own fitness.  Humans are the only organisms that abort their own fetuses, that blow themselves up in support of an ideal, that have civil wars, killing people in fact most closely related to them. But humans also rescue strangers from drowning, and grow food to be consumed by people across the world.

We can devise all the equations we want about kin and fitness, and we can calculate the heritability of this trait and that, to show that behavior is genetically determined, but our thinking brains, and the power of culture trump those rules.  Members of Homo sapiens simply are not just bags of 'selfish' genes, and meaning isn't just reproduction.  We're not nearly as hard-wired for behavior as many other 'lesser' species of animals and plants are often (correctly or incorrectly) assumed to be.