biology, evolution, journal club, parthenogenesis, science

Snake parthenogenesis II: Non-virgin virgin birth

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So, in the last post, we went through some of the strange and interesting things associated with the Boa constrictor that gave parthenogenetic birth to 22 baby Boas. It turns out there’s yet another crazy thing going on here. Etymologically speaking, parthenogenesis means “virgin birth.” It is a combination of parthenos (παρθένος), meaning “virgin,” like the parthenon, and genesis (γένεσις), meaning, well, genesis.

The thing is, though, while it seems clear that the baby Boas’ genetic material comes entirely from the mother, she’s likely not really a virgin. I don’t mean that she’s a born-again virgin who had some had some wild times back in snake college, repented, then ran for Senate. Instead, it appears that she only gave birth after being housed with a male snake. Of course, it’s only two litters, so it could well be a coincidence. On the other hand, it could be that fertilization was required to initiate development of the diploid eggs produced by the female.

There is a somewhat related phenomenon of paternal genome loss that has been identified in several different species of creepy crawlies, including at least some species of Phytoseiid mites (click here for non-English text, but drawings of them preying on other mite species), scale insects, and sciarid flies. Typically, paternal genome exclusion is limited to males, which start of diploid, but then lose their paternally inherited genome at some point during development, often living much of their lives in a haploid state. These and related phenomena are nicely covered in chapter 10 of Genes in Conflict by Austin Burt and Robert Trivers. Of course, the difference here is that the snakes have two full maternal genomes. Also, we don’t really know if they received, and then jettisoned paternal genes, or never got them in the first place.

It also bears some similarities to one of the mechanisms by which uniparental disomies arise in humans (among others). Normally, meiosis results in one copy of each chromosome going into each gamete. With some frequency, though, they don’t sort out correctly, and two aneuploid gametes wind up being produced, one with an extra copy of one chromosome, and one that is missing that chromosome altogether. If one of these gametes winds up contributing to the offspring, that offspring may wind up missing one copy of a chromosome (e.g., the X chromosome in Turner’s syndrome), or with an extra copy of a chromosome (e.g., the X chromosome in Kleinfelter’s syndrome, or chromosome 21 in Down syndrome). Another possible outcome for the extra chromosome case is “trisomy rescue,” where the zygote somehow recognizes the presence of the extra chromosome and kicks out one of the three copies.

There are a couple of different ways that this trisomy rescue can happen. Let’s say the extra chromosome came in with the egg. If one of the two maternal copies is kicked out, you wind up back at the standard diploid genome. On the other hand, if the paternal copy gets kicked out, you have the standard number of chromosomes, but a uniparental disomy. If the chromosome contains one or more imprinted genes, this can have various developmental consequences.

So, one possibility is that this female snake, for whatever reason, produces diploid eggs. Fertilization triggers development, but then a triploid rescue mechanism kicks in. The key thing is that it would need to be kicking in before fusion of the maternal and paternal pronuclei, since it seems to be the paternal genome that goes missing in every case.

Or this could all be related to the fact that the males snakes housed with this female in 2009 and 2010 were all huge General Ripper fans.

Update: One more follow-up post here.

biology, evolution, genomic imprinting, journal club, parthenogenesis, science

Parthenogenesis: now in snakes!

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So, as if my friends on the religious right needed more reasons to be afraid of snakes, now they are threatening to undermine the nuclear family, which is clearly defined in the Bible as a mommy, a daddy, and two overachieving children. A recent paper in Biology Letters has studied two litters of offspring from a female Boa constrictor, totaling 22 baby snakes. All of the babies are female, and all of them have a rare, recessive color trait that is exhibited by the mother, but by none of the possible fathers.

What the researchers were able to demonstrate was that these baby snakes do not have a father at all. Rather, they are all parthenogenetic products of the mother. The researchers typed the offspring at eight microsatellite loci, and all the daughters were homozygous at all of the loci, matching in each case one of the two maternal alleles.

Note to self: No Boa constrictors on the island!

Several interesting things here. First, the implication is that these daughters are genome-wide homozygotes. This suggests a complete absence of lethal recessive mutations in the mother’s genome. This seems surprising, but let’s do a quick back of the envelope calculation. Let’s assume there are about 10,000 genes in the snake where a loss-of-function mutation is lethal. Say the coding region for each gene is about 1000 nucleotides long, and that, say 1/10 of those nucleotides are fixed, in the sense that a mutation obliterates the gene’s function. That would be a lethal mutational target of 100 nucleotides for each gene. Assuming a mutation rate of 10-9, mutation-selection balance at each locus would have loss-of-function mutations circulating at a frequency of about 1 in 3000. So, we would expect each maternal half-genome to contain, on average, about 3 lethal recessive mutations. Assuming that those mutations are Poisson distributed, there is about a 5% chance that it would contain no such mutations. So, not super likely, but not out of the question either. And, that probability would be higher if the mutational target is smaller, or if the Boa population has undergone significant inbreeding, which would have driven the frequency down.

Second, there’s a weirdness with the sex chromosomes. Now, in mammals, sex is determined by whether you have two X chromosomes, in which case you are a female, or an X chromosome and a Y chromosome, in which case you are a male. Everyone inherits an X chromosome from their mother, and you inherit either an X or a Y from your father. So, if you don’t have any sons, it’s not your wife’s fault. Snakes also have chromosomal sex determination, but use a ZW system. Males have two Z chromosomes, while females have a W and a Z. It turns out that every one of the parthenogenetic daughter snakes is actually WW. That’s some serious weirdness on which I have little insight. The one thing we can say is that you would never see a YY male. The Y chromosome is a shriveled little thing that does not do much other than tell you to be male, while the X does all the work. The snake W chromosome, on the other hand, is a real chromosome, that is, in fact, impossible to distinguish from the Z under the microscope.

Finally – and this is the reason I’m writing about this here – this tells us something about genomic imprinting. In mammals, there appear to be at least 50-100, possibly as many as 1000 imprinted genes, which are expressed from only one of the two copies. So, if there are 200 imprinted genes, there will be, say, 100 of them that are expressed only from the paternally inherited copy. If you produce parthenogenetic offspring, they will inherit two maternally derived alleles at each of these loci, which will be like having 100 of your genes knocked out, and is almost guaranteed to be lethal. In fact there are a number of genetic disorders in humans that result from uniparental inheritance of just a small subset of imprinted genes, and these produce fairly severe phenotypes. So, the fact that these parthenogenetic snakes appear to be perfectly viable implies that there are few – or quite possibly no – imprinted genes in this species.

Booth, W., Johnson, D., Moore, S., Schal, C., & Vargo, E. (2010). Evidence for viable, non-clonal but fatherless Boa constrictors Biology Letters DOI: 10.1098/rsbl.2010.0793

Update: Two follow-up posts here and here.

biology, evolution, journal club, media, science

The flux capacitor in your brain

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So, you already know that Friday was the 55th anniversary of Doc Emmett Brown’s falling off his toilet, hitting his head, falling unconscious, and coming up with the flux capacitor, which not only allowed Teen Wolf to make out with Caroline in the City, but is singlehandedly responsible for the fact that anyone still remembers what a DeLorean is. How do I know you know? Because you spent all week baking this cake.

It took the good doctor thirty more years to get his idea working, so that time travel first became practical in 1985. However, it turns out that, as usual, natural selection got there first. There is an article in press in the Journal of Personality and Social Psychology that presents experimental evidence for precognition or time-reversed instances of causation. The preprint is available here, from the website of the author, Daryl Bem.

Bem is fairly well known, particularly for his early work in social psychology on the “self-perception theory of attitude change,” which is basically that we learn about ourselves in much the same way that someone else might. For instance, say I hate peanut butter sandwiches. But then I eat a peanut butter sandwich every day for a month. I then look at myself, and say, “Hey, that handsome fellow really seems to like peanut butter sandwiches.” This is the academic basis of that damn Stuart Smalley sketch. He is also responsible for the “Exotic becomes erotic” theory of the formation of sexual orientation.

The paper presents the results of nine experiments, each of which tested for awareness of future events. In the first experiment, subjects were told that there was a picture behind one of two (virtual) curtains, and they were supposed to guess which one. When the picture was just a picture, they picked the right curtain 49.8% of the time, which was not significantly different from the expected 1/2. But, when it was an EROTIC picture, they picked the right picture 53.1% of the time, which, while not particularly overwhelming, is apparently statistically significant at the p=0.011 level. There are eight more experiments on retroactive priming, precognitive avoidance of negative stimuli, and retroactive habituation and induction of boredom. The article also includes discussions of random number generators, pseudorandom number generators, quantum mechanics, and Alice in Wonderland.

So, if you read to the end of this blog post in the hopes that I would tell you what the hell is going on here, I’m afraid I’m going to leave you disappointed. Although, to be fair, your precognitive boredom should have known that I would have nothing intelligent to say sometime around the slash-fic link, in which case you’ve long since moved on. I’ll just lay out the obvious candidates. First, it’s pure chance, although getting consistent results across nine experiments makes this seem not terribly likely. Second, these are nine of a much larger number of experiments, most of which did not conform with the experimenter’s expectations, and were therefore viewed as flawed and discarded. Third, there is actual manipulation of the experiments and/or data, either consciously or unconsciously. Fourth, there is some small possibility of some crazy-cool, Dune-esque, Jedi stuff going on here that is someday going to completely revolutionize how we understand cognition, causation, and time.

Personally, my money is on some combination of options two and three. Even without any type of fraud going on, I think it is incredibly easy for us as scientists to be so convinced that we know what the outcome of an experiment is going to be, that we can massage things around the margins. Keep in mind that these effects are only a couple of percent. On the other hand, even the smallest possibility of number for justifies, to me, the entire institution of tenure. This is exactly the sort of nut-bag research program that you can only pursue if you have absolute job security. I wish that more tenured faculty pursued research like this.

culture, media

What’s the Swedish internet made of?

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So, if you’ve never played with Google Analytics, I highly recommend it. It is awesome. You can see who came to your website, where they came from, and what they were actually trying to find when they fell victim to your amateurish attempts at search engine optimization (“Sexy Megan Fox bikini pix!! Sexy Megan Fox bikini pix!!”). You can sort them by operating system, web browser, social security number, or alphabetically by password. It’s the second best way to waste huge amounts of time on your computer – the best if you work at a place with content filtering.

For example, last week, I got a hit from Georgia. Not the Coca Cola and Peaches one; the Stalin and fighting-with-Chechens one. This person got to the site by searching for “ჯონ ვილკინს” on Google, which I can only assume is Kartuli for “People’s 2010 rankings of the top 100 sexiest evolutionary biologists.” It’s an incredibly efficient language.

A couple of days ago, I got a hit from Sweden. Yes, the ABBA and Volvo one. In this case, the interesting thing was the service provider: “handelshogskolan.” Now, we know that the American internet is a series of tubes. Well, apparently so is the Swedish internet, but their tubes are made out of pig intestines. Sadly, that means that from now on, when I hand my e-mails to my hamster, Hedwig, and send her off, I’m going to have to mentally revisit that whole Richard Gere thing.

biology, evolution, Politics, science

Democrats investing in kleenex, socks in wake of midterm elections

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So, yesterday’s election turned out rather poorly for Democrats.

On a completely unrelated note, I wanted to draw attention to a paper published in Biology Letters that investigates the ejaculatory strategies of male flour beetles of the species Gnatocerus cornutus. As in many species, G. cornutus males engage in pre-copulatory sexual selection, where males fight, and the winners get privileged access to mates. The researchers, at Okayama University, find that the losers of these fights appear to shift to a strategy that focuses more on sperm competition, through increased “ejaculatory investment.” Winning a fight has no effect on the number of sperm “transferred” during a copulatory event. However, losers show two effects that indicate a strategic shift: they are less aggressive towards other males, and they increase their sperm transfer by nearly two-fold.

By the fifth day after losing the fight, both aggressiveness and sperm-transfer levels return to normal, so we can expect a return to Republican levels of “transfer” sometime this weekend.

biology, evolution, genomic imprinting, primers, science

Genomic Imprinting II: Inclusive Fitness and Conflict

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So, as we discussed previously, genomic imprinting is the phenomenon where the pattern of expression of an allele differs depending on whether that allele was inherited from your mother or your father. This difference in expression does not depend on differences in the DNA sequence of the two alleles. Your two alleles might have identical DNA sequences, but function completely differently.

For example, one of the two alleles might be epigenetically silenced. That is, because of reversible chemical modifications to the DNA, or to proteins that are closely associated with the DNA, that allele would be inactive. The other allele, with an identical DNA sequence, but different modifications, would be happily chugging along producing its gene product(s). Today’s question is, “That seems crazy! Why would you do something like that?”

One of interesting (and by “interesting” I mean “sad”) things about evolutionary biologists is that whenever something genuinely new and surprising is found in the world, everyone feels the need to propose an evolutionary explanation for it, whether new explanations are needed or not. So, many attempts to explain the origins of imprinting have been proposed, most of which are consistent with at least some of the data, and a few of which actually make sense. There is one explanation, however, that is far and away the most successful in explaining the distribution and nature of imprinted genes: the “Kinship” or “conflict” theory of imprinting. This theory owes its creation and early development primarily to David Haig (who laid out the theory originally in papers with Mark Westoby and Tom Moore).

The basic idea of the Kinship Theory is that natural selection favors different expression behaviors for maternally and paternally inherited alleles. That is, the optimal level of expression for an allele that is maternally inherited is different from the optimal level for a paternally inherited allele. Now, if you think about that for a minute, it probably seems strange. I mean, if I survive and reproduce, that’s equally good for any of my genes, independent of where I got them from, right? Right?

The key is recognizing that natural selection favors allele that pass on the largest number of copies to future generations. (“Isn’t that what I just said?”) AND, that it doesn’t matter whether those copies are passed on directly by my having children, or if they are passed on because because one of my relatives, who has inherited an identical copy of that allele, has children. There are different ways to represent this (which are all mathematically equivalent if you do them right), but the one that I find most intuitive is the idea of “inclusive fitness.” Basically, we can think of natural selection as maximizing the inclusive fitness of an allele, which is the fitness of every individual in the population, weighted by the probability that they carry the allele. In the simplest model, this probability is 1 for me, 1/2 for a sibling, 1/8 for a cousin, and so on.

Now, think about your relatives. With the exception of your descendants, your full siblings, and their descendants, all of your relatives are related to you either through your mother or your father. That means that, in general, this inclusive fitness calculation will be different for maternally and paternally derived alleles. Therefore, there will be a conflict, where the phenotype that would maximize the inclusive fitness of your maternally inherited allele will be different from the one that would maximize the inclusive fitness of your paternally inherited allele. If this difference is large enough, it can actually drive alleles to take on two different conditional expression strategies, and, voila, imprinting.

Granted, even in the most extreme cases, this difference is likely to be pretty subtle, which might make it seem strange that this could explain a situation where one of the two alleles is completely turned off, while the other one is cranking away. This phenomenon, where a little conflict leads to a big effect, will be the subject of the next installment.

biology, evolution, music, science, sex

On sex and singles

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So, the post title is clearly designed to pump up pageviews, but those of you who have come here hoping to see photos of me with dollar bills hanging out of my G-string are going to be sadly disappointed. The good news is the money you’ll save having your corneas scraped.

This post is actually about the evolution of sex, or “recombination,” as the biologists like to call it. The question is, why does sex exist? Or, at a genetic level, why would an organism do something that passes on only half of its genes (by mating with something that donates another half), rather than simply making a genetic copy of itself. This is often referred to as the “two-fold cost of sex.” Presumably, there must be an evolutionary benefit to sex that is great enough to overcome this two-fold cost.

As with everything in evolutionary biology, there are an enormous number of theories that have been proposed to explain the evolution of sex, but there are two major arguments. One is that sex allows beneficial mutations that arise on different backgrounds to be recombined onto a single genetic background. This allows adaptive evolution to occur at a faster rate. The other (which is really sort of another side of the same coin) is that sex permits more efficient purging of deleterious mutations.

Let me use an analogy that requires us to take a walk down memory lane. You kids may not know this, but a long time ago, music came on albums, which contained a bunch of songs. The problem with the album system was that most bands would put out one good song, and then fill the rest of their album up with crap. So, to get a collection of good songs, you had to buy a whole bunch of other songs that you didn’t actually want. Sure, you could buy the 45, but who did that, seriously?

So, in this analogy, the first theory, the one about beneficial mutations, is like how you would take all of your albums and put the best songs together on a mix tape that you give to a girl you’re trying to impress. Yes, back then, this was done non-ironically by people who were not hipsters. She would then listen to the first few songs out of a sense of politeness, make some awkward comment about how knowledgeable you are, and then mysteriously change her phone number.

One of the great things about the advent of mp3s and digital music sales is that it is easier to hide your embarrassing musical taste. It used to be that your friends would always pull out your Night Ranger album and make fun of you. Now you can rock out to Ke$ha and just close your computer when someone knocks on your office door.

Also, and more relevantly, it is easier and more natural now to buy individual songs. So, you don’t ever wind up owning a whole pile of non-I’m-Gonna-Be-(500-Miles) Proclaimers songs. Music has undergone a transition to where it is more like our second theory, where recombination permits the elimination (through failure to purchase) of deleterious mu(sic)tations.

I’d write more, but there’s a pile of cash on the dresser that I need to count.

biology, evolution, Hemiscience, media, science

On evolution and sequels

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So, there are a lot of things in evolution that seem like they are moving in one direction, when actually they are moving the opposite way. Or maybe it’s the other way around – I forget. For instance, one of the things that we know is that the vast majority of naturally occurring mutations are deleterious. That is, just like your crotchety old grandfather always said, children are, on average, a little bit worse than their parents (and the music they listen to is A LOT worse). Yet, somehow, evolution is able to maintain a level of function in the face of these deleterious mutations, and even to create new adaptations.

The reason is natural selection. Children will be worse than their parents on average, but there will be variation. Some will be a lot worse, and some only a little worse. Some may even be a bit better. The key is that the better children will, on average, produce more grandchildren than the worse children will (so your nagging mother was also right). It’s a bit like walking the wrong way on one of those people-movers at the airport.

Of course, there is also noise in the system. Sometimes a big rock falls on the “fittest” individual in a way that has little to do with that individual’s genotype. And sometimes an individual carrying a lot of deleterious mutations starts a polygamous cult and has about a hundred kids. But on average, the filtering effects of selection seem to counterbalance, or even outweigh the effect of those deleterious mutations.

This got me wondering if there was maybe something similar going on with movie sequels. The conventional wisdom in most quarters is the movie sequels suck. Sure, there is the occasional Godfather II, but for every one of those, it seems like there are a hundred films that are closer to Highlander II. So, I did a little study [1], in which I compared three classes of films: movies that got sequels, movies that are sequels, and random movies. Two scores from Rotten Tomatoes were collected for each movie: the “tomatometer” score, which is the percentage of reviews of the movie that were positive, and the user score, which is the average rating (out of 10) by users of the site.

The average scores are:

Movies with sequels: 59.2% positive 5.92 average (coincidence, or Illuminati plot?)
Movies that are sequels: 44.8% positive 5.16 average
Random movies: 45.7% positive 5.21 average

So, what’s our conclusion here? Well, it seems like sequels are, on average, pretty darn similar in quality to the random sample of movies. The outlier is the set of movies that get sequels made. So, maybe we think that sequels suck because we tend to mentally compare them with the originals, and, like our high-school sports careers, they fail to live up to expectations. Maybe sequels suck because movies suck, and a sequel is no more or less likely to suck than anything else. Or is there something about sequelness in itself?

We can drill a little deeper by dividing our movies into five quintiles (with ten movies each) based on the tomatometer scores of the originals:

Bottom quintile:
Movies with sequels: 17% positive 3.6 average
Sequels of movies: 15% positive 3.6 average

Second quintile:
Movies with sequels: 45% positive 5.2 average
Sequels of movies: 22% positive 4.0 average

Third quintile:
Movies with sequels: 58% positive 5.9 average
Sequels of movies: 49% positive 5.3 average

Fourth quintile:
Movies with sequels: 82% positive 7.0 average
Sequels of movies: 64% positive 6.1 average

Top quintile:
Movies with sequels: 94% positive 7.9 average
Sequels of movies: 74% positive 6.8 average

What this makes it look like is that there really is something about making a sequel that makes your movie suck more than the original. For the most part, you can expect a 15-20% drop in the number of favorable reviews going from the original to the sequel, even if the sequel was only average to begin with. The one exception is the bottom quintile, where you can expect your sequel to suck just about as much as the original did. This may be a boundary effect, as the average number of positive reviews is bounded at zero. This is the great thing about making “Baby Geniuses 2” is that it is virtually impossible to underperform “Baby Geniuses.” On the other hand, with a tomatometer score dropping from 2% to 0%, the baby geniuses somehow managed it.

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[1] Not-very-scientific study methodology:

In order to collect a sample of sequels, I went to Rotten Tomatoes, and searched for “2” and “II,” discarding anything that was obviously not a sequel, or for which there was no rating information available. This yielded a list of 50 movies, including “2 Fast 2 Furious,” but not “Aliens.” For each of these, I got the “tomatometer” score and the average user rating for that movie and for the movie of which it was the sequel.

For the random sample, I went to The Movie Insider, and used their list of January-June 2009 releases. I discarded anything that was a foreign film or documentary that had an initial release date prior to 2009. The rationale here was that if a documentary is shown at film festivals in 2007, and then gets a major theatrical release in 2009, this is not a random movie. It is a movie that has already undergone a fairly intense selection process. In the end, this list had 75 movies in it.

The study was not double-blind or vetted by anyone else, and undoubtedly contains errors in both transcription and judgment. However, hopefully it is close enough for analogic use.

About this blog

Why "Lost in Transcription"?

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So, I like to imagine that people are reading this blog, that they are intrigued by its content, and it’s got them wondering, “Why is this blog called ‘Lost in Transcription’?” As I noted in the pilot, the aim here is to talk about poetry and science, particularly those parts of science that are related to my own research, where I can claim some degree of expertise. The title is meant to bridge between these two worlds.

First, in the literary domain, it is a play off of the phrase “lost in translation,” which appears any time there is a discussion of either literature, of cultural differences, or of Scarlett Johansson that goes on for longer than ten minutes. Within poetry, its two most famous appearances are as the title of a James Merrill poem (perhaps the best poem ever written about working a jigsaw puzzle), and in a quotation attributed to Robert Frost, that “Poetry is what gets lost in translation.”

Within genetics, translation refers to the process by which an RNA sequence is read to generate an amino acid sequence. In a related process called transcription, DNA serves as a template for the synthesis of RNA. One of the topics that I work on is genomic imprinting, where one of the two gene copies in a cell has its transcription silenced. So, in a strictly literal sense, a better title would have been something like “loss of transcription,” but if you are willing to stretch with me, we could imagine that at a genetic locus that is subject to genomic imprinting, the genetic information from one of your two parents is Lost in Transcription.

Behavior, culture, Politics

On aging, conservatism, and experimental economics

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So, it is standard conventional wisdom that people are liberal when they’re young, and conservative when they’re old. To the extent that we interpret “liberal” as “eager for change” and “conservative” as “against change,” this trajectory is only natural. Especially in the modern world, where things are changing all the time, it may simply come down to a difference in experience: you’re less likely to pine for the way the world was thirty years ago if you weren’t alive thirty years ago.

But what I am really interested in here is the apparent trend where people become more conservative with respect to economic policies. In this context, the argument about familiarity does not seem to hold. In the United States, the government’s economic policies have been trending more conservative for decades, and the familiarity argument would predict that older people should be, on average, more liberal. However, there is a different aspect of familiarity that may be relevant, as it pertains to our beliefs about human nature.

A key aspect of the economic debate between liberals and conservatives is a difference in the assumptions they make about how people will behave when left to their own devices. If you will forgive me for painting complex things with a simple brush, the cartoon versions of these are something like this. Conservatives believe that people are inherently self-serving and lazy, and will work hard only if they are given tangible incentive to do so. From this perspective, progressive tax structures and government programs like welfare and social security are problematic because they take away the incentive to earn money. Liberals, by contrast, believe that everyone is trying hard, that inequality comes largely from societal structures that are beyond individuals’ control, and that people should not be punished for the inherent unfairness of society (except maybe those at the top of the pay scale, who have benefitted most from those inequalities).

Now, the most obvious difference between young people and old people is that old people have a lot more experience with other people than young people do. That is, we tend to start out with positive views about human nature, but over time we interact with more and more people, they disappoint us, and we become progressively more cynical. Many conservatives see this as evidence in favor of their position: we start naive, and become conservative when we learn what people are actually like. However, I want to suggest a different explanation, having to do with asymmetries in how we perceive positive and negative deviations from our expectation. Intuitively, this comes down to the fact that we notice whenever we get stopped by a red light, but often don’t notice when we hit a green light. Therefore, we perceive that stoplights are red more often than they actually are.

This also happens in the economic domain, as has been extensively documented by experimental economists in a variety of “public goods” games. The basic structure of these games is as follows. You have a group of people, say 10, and you give each of them some money, say $10. Each person can then contribute a fraction of their $10 to the “pot.” The money in the pot is the multiplied by some factor, say 5, and then distributed equally among the ten players. So, if no one contributes anything, everyone gets to keep the $10 they were given at the beginning. If everyone contributes the full $10, the pot has $100, which is multiplied by 5 to give $500, which is distributed back to the players, and everyone walks away with $50.

The ideal thing for the group as a whole is for everyone to contribute the maximal amount. However, the ideal thing for the individual is to contribute nothing (and to hope that everyone else contributes the maximum). For example, if I contribute nothing, and everyone else contributes $10, I walk away with $55, and everyone else walks away with $45. If I contribute $10, and no one else contributes anything, I’ll get $5, and everyone else will get $15. From an “economic rationality,” “Nash equilibrium” perspective, the thing to do is contribute nothing. However, this is not what happens in practice.

In a wide variety of experimental setups, what people actually do is contribute about 50% of what they are initially given. So, the typical outcome in our experiment would be that everyone contributes about $5, which makes $50 in the pot, which is multiplied to $250, and everyone walks away with $30 (the $5 they kept plus $25 from the pot). Across a broad range of cultures, ages, quantities of money, etc., people come into these experiments with a somewhat liberal perspective, as they seem to both trust the good will of the other players, and care about the results for the group as a whole.

However, if we play the game over and over again, an interesting thing happens: the average contribution gradually declines, until eventually, no one is contributing anything to the pot. Based on interviews with the participants in these games, economists believe that they understand this trend. Let’s say that one person contributes $5, which is the average among the group, but some people contribute $4, and some $6. This person will not really think about the people who gave $5 of $6, but will think a lot about the people who gave $4, get pissed off, and reduce their contribution in the next round. While it is mathematically trivial that people, on average, contribute the average amount to the pot, it seems to be psychologically true that people perceive themselves on average as having made an above-average contribution.

What I think is that something analogous happens over the course of the lifetime of an individual. We meet some people who are hard working, and some who are lazy, but there is this perceptual bias that means that the lazy, selfish people we meet weigh more heavily in our developing opinions about “what people are like.”

The other interesting finding from these experiments is that it is remarkably easy to reset the spiral of cynicism. If you take the participants out of the room, give them a cup of coffee, and let them use the bathroom, when they go back in, they often go right back to contributing 50% on average. So, note to Democratic lawmakers, if you can figure out how to let the country drink a collective cup of coffee and use the collective bathroom, you may find a dramatic increase in support for social programs and a progressive tax structure.

Science, Poetry, and Current Events, where "Current" and "Events" are Broadly Construed