Category: Science

Here is a Harvard-made video of the inner life of a cell.

(CHT: Steve Ray.)

GET THE (AMAZING!) VIDEO!

Now if only I had enough molecular biology background to understand it all–or someone to explain it all to me.

(CHT to the reader who e-mailed!)

Yeah, the ending is a little dark, but it should only cause the Pluto haters to think more deeply about what they have done.

The International Astronomical Union, meeting last week, adopted an official definition of what constitutes a planet, with the result that we have two new planets: Ceres and "Xena"! Yippie!

Now, before you say to yourself, "What planet has he been on?", yes, yes, I know: Under the IAU definition these bodies–together with Pluto–are classified as "dwarf planets," rather than planets sans phrase, but dwarf planets are still planets, just as dwarf humans are still humans.

That’s my story, and I’m sticking to it. 😛

Now, let’s talk about the definition they finally coughed up:

The IAU . . . resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A "planet" [1] is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects [3] except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Footnotes:

[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
[2] An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects [SOURCE].

The condition that keeps Pluto, Ceres, and "Xena" from being planets sans phrase is condition 1c, which is that the body "has cleared the neighbourhood around its orbit."

That’s totally stupid.

Not only is it unacceptably vague (just how clear does the orbit have to be?), it also has nothing to do with the nature of an object. It has to do with the object’s relationship to other objects, and as I’ve already said, what an object is is more important than where it is if you want to talk about its nature. By including a relational term in the definition, the IAU seeks to establish "planet" as a partly natural, partly relational category, and that’s just scientifically inelegant.

(Incidentally, criterion 1a–about going around the sun–is another dumb relational term.)

What we should be trying to do here, in coming up with a definition for a planet, is try to capture the natural essence of those bodies which have come to be regarded as planets, and the only essential criteria that I can see for them is that they (a) don’t glow (no fusion) and (b) are big enough that their gravity causes them to be round.

Saying that they’ve cleared their orbit is superfluous. That means that you could have an object the size of Jupiter in an orbit filled with asteroids and deny it the status of a planet sans phrase on that basis. It would make the Jupiter-sized object a "dwarf planet" even though it drawfs the Earth!

Dumb! Dumb! Dumb!

In fact, some folks have argued that this situation is precisely the one that we’re in:

There continues to be much criticism regarding the final draft of the definition. For instance, the lead scientist on NASA’s robotic mission to Pluto, Dr Alan Stern, contends that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones either. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. "If Neptune had cleared its zone, Pluto wouldn’t be there," he added [SOURCE].

Put that in your pipe and smoke it, IAU! Jupiter as a "dwarf planet"!

Fortunately, I think this definition is likely to get revisted in the future. Not only is it scientifically gerrymandered, but

The orchestration of the final vote has come under criticism because of lack of participation due mainly to the time of the vote. The final vote was taken on the last day of the 10-day event after many had left or were preparing to leave. Over 2,700 astronomers attended the conference, but only 424 remained on the last day. There is also the issue of many astronomers who are unable to make the trip to Prague [SOURCE].

Once the broader membership of the IAU has had a chance to weigh in, a considerable fight may start and the issue may get revisited at a future convention.

Further, the inelegant nature of the definition may force itself upon the minds of current or future astronomers with sufficient force to force a reconsideration. Or further scientific discoveries may.

Let’s hope that next time they get it right: Figure out the essence of the object you’re talking about and go with that, regardless of what the conclusions are.

In the meantime, I’m happy to be living in a solar system with eleven planets: eight planets sans phrase and three dwarf planets.

Things are happening fast and furious at the International Astronomical Union (IAU) regarding the upcoming planet definition vote that’s scheduled for this Thursday.

And Wikipedia’s on the story!

In the open-source information age, their 2006 Redefinition of Planet page has not only been created since last week’s announcement of a proposed definition but has been updated to reflect the current state of play.

I was particularly interested to see some of the criticism directed against the proposed definition. Not only have other critics agreed with me that one shouldn’t limit planets to just things that are orbiting stars, they have also made the same criticism I did of defining a moon based on where the barycenter of a planetary system is located.

In fact, they went beyond what I said and made new criticisms of this (dumb) idea:

[W]hile the Moon is defined as a satellite of the Earth, over time the Earth-Moon barycentre will drift outwards (see Tidal acceleration) and be situated outside of either body. This would then upgrade the Moon to full planet according to the redefinition. The time taken for this to occur is expected, however, to be billions of years.

In the extreme case, where a double body has the secondary component in a very eccentric orbit, this could lead to a drift of the barycentre in and out of the primary body, leading to a shift in the classification of the secondary body as a satellite or planet, depending on where in its orbit it is.

All of which underscores the point I made last time: What an object is rather than where the object is should determing whether it is a planet.

Now, I don’t know what the IAU will do this Thursday when they finally vote. Wikipedia reports that one group voted early with negative results:

According to Alan Boss of the Carnegie Institution of Washington, a subgroup of the IAU met on August 18, 2006, and held a straw vote on the draft proposal: only 18 were in favour of the draft proposal, and over 50 against. The 50 in opposition preferred an alternative proposal drawn up by Uruguayan astronomer Julio Ángel Fernández.

That alternative proposal would demote Pluto from planetary status.

Whether or  not the draft definition passes, I doubt that Thursday’s vote will see this kind of lopsided vote in favor of the Fernandez alternative. The group in question was (a) relatively small (68 people, when there are more than 2000 at the meeting) and (b) clearly highly motivated on the subject or they wouldn’t have held a preliminary vote like this. This strikes me more as an attempt to influence the course of events than a representation of what opinion in the IAU is on the topic.

A different indicator of opinion in the IAU is as follows:

Owen Gingerich, an historian and astronomer emeritus at Harvard who led the committee which generated the original definition, predicted the Executive Committee, "will undoubtedly come before the membership with a single resolution. They may make some adjustments." He added that correspondence he had received had been evenly divided for and against the proposal.

YEE-HAW!

Who doesn’t like a cliffhanger scientific scrap!

GET THE STORY.

MORE FROM SPACE.COM.

Earlier I said I’d offer my own thoughts on the proposed IAU definition of what a planet is, so here goes . . .

I am largely . . . pleased.

The basic reason that I’m pleased is that the number of planets is going up. What could be better than new planets? In fact, if the definition sticks, the largest expansion of the number of known planets in human history may occur in our lifetimes! Yee-haw!

It would be a real downer, in fact, if they had gone with a definition that stripped Pluto of its status as a planet. That would have been a disappointment. It would have created a feeling that there was an eighty-year mistake that was being undone, and since the definition of "planet" is largely arbitrary (as is the case for most words), why go through the hassle of trying to convince everyone in the world that Pluto is not a planet when a definition could be crafted that could easily accomodate the idea?

I mean–I know that some people (such as canonist Ed Peters, and more power to him) have been gleefully dancing on Pluto’s grave for some time–but the idea of Pluto is a planet is just too deeply embedded in our culture to try to get everyone to stop referring to it as a planet. Think about the practicalities of doing that. Ick. It’d be much easier just to accomodate the definition of "planet" so that Pluto counts.

Put another way: It’s easier to get people used to the idea of accepting new planets than declassifying ones they grew up with.

So I think the IAU’s committee made the right decision in keeping Pluto as a planet.

This still leaves open the question of what kind of definition they would use.

One definition that I would have been okay with would be to simply draw an arbitrary line and say "Pluto is the smallest planet by definition. Any thing with a larger radius or mass than Pluto is a planet. Anything that has a smaller radius and mass than Pluto is something else."

I’d be okay with that–and on that formulation we’d only get one new planet (Xena)–but it’s scientifically inelegant. It just draws an arbitrary line instead of basing the definition on a natural kind.

A natural kind (as the term is here being used) is a distinct type of thing that you find in nature. For example, lions and ants and daisies and geodes and geysers and rainbows are natural kinds. They aren’t all living, and they are categories that have fuzzy boundaries, but they are things that you find in the universe that are significantly similar to each other to form a kind and sufficiently distinct from other things that humans are inclined to come up with a unique word for them.

I’d much rather see the definition for "planet" be based on the kind of object that people have traditionally called a planet than simply drawing an arbitrary line.

One reason for this is that the arbitrary line that could have been drawn for Pluto is quite close to the kind of line that would suggest itself if we based the definition of planets off of natural kinds.

One thing that all the traditional planets have in common is that they are at least roughly spherical (i.e., they’re sphereoids), and this is no accident: It’s because they all have a certain mass, which compresses them into a sphereoidal shape, rather than letting the structural properties of the material they’re made out of determine their shape (as with many asteroids, which are basically chunks of rock that aren’t spherical at all or at least aren’t spherical due to gravity).

This mass-based definition also coheres with our intuition that a planet should be a body of a certain size, rather than any ol’ fleck of rock we find in the solar system.

If we go with a natural kind-based definition, the obvious lower threshhold for what counts as a planet is the massive-enough-to-be-a-sphereoid level. That’s still a fuzzy line that leaves room for further clarification (just how sphereoidal does it have to be?), but at least it’s not completely arbitrary.

The problem with proposing this as a lower threshhold is that a lot of objects in the solar system meet this test, and in coming years we’re probably going to find many more. Personally, I find the idea of lots of new planets cool, but it’s also quite an adjustment for many people, and so I’m impressed by the IAU’s willingness to go with the more scientifically elegant definition rather than an arbitrary definition based on Pluto’s size that would be more restrictive of the number of new planets.

What I’ve said above covers the lower threshhold of what counts as a planet under a natural kinds definition, but that still leaves the question of what the upper threshhold would be. This is something the IAU’s proposed definition doesn’t deal with, but I think there is an obvious natural kinds-based line to be drawn there as well: If an object becomes so massive that–at some point during its life cycle–it undergoes nuclear fusion then it is no longer a planet but a star (or a dead star if it’s nuclear fuel is spent and fusion has stopped).

My preferred natural kinds-based definition of a planet is thus:

An object is a planet if and only if:

1) It is massive enough that its shape is dictated by its gravity rather than by structural factors (i.e., it’s massive enough to be a sphereoid) and

2) It is not so massive that nuclear fusion naturally occurs in it at some point.

Unfortunately, the IAU didn’t go all the way to my preferred natural kinds definition. It didn’t treat the second criterion explicitly (though it did distinguish planets from stars), and it went beyond my definition by adding what I consider to be an inelegant, arbitrary, and . . . frankly . . . stupid criterion–one based on where an object is.

Specifically, the IAU’s proposed second criterion was:

(b) is in orbit around a star, and is neither a star nor a satellite of a planet.

This is just dumb, and I suspect it won’t survive long term.

One reason is that not all planets are in solar systems. There are bound to be objects that are otherwise identical to planets that have been flung off from solar systems, and to refuse to call intersolar planets "planets" just because they aren’t orbiting around stars is dumb. If we had a close encounter with something that knocked one of the classical planets out of our solar system, we wouldn’t say it should be declassified as a planet just because it isn’t orbiting the sun any more.

The other bit of this criterion that I don’t like is that to count as a planet an object must not be "a satellite of a planet."

A satellite–as they’re using the term–means any object that is non-massive enough that the barycenter it orbits is within another object.

Now, in case it’s been a while since you had physics or astronomy or an equivalent course, a barycenter is a point that two or more objects are orbiting. Y’see (forgive me if I oversimplify a bit), whenever two or more objects are in a stable orbital system (or subsystem), the masses of the objects are all pulling on each other in a way that they orbit a single point.

This point is not simply the center of the largest object, so when the Moon "orbits" the Earth, it isn’t swinging around the center of the Earth. It’s swinging around a point that is part way between the center of the Earth and the center of the Moon. That point is known as the barycenter, and–because of the relative masses of the Earth and the Moon and their distance from each other, the barycenter of the Earth-Moon system is inside the Earth.

But it doesn’t have to be that way. If you had two equally massive objects orbiting–if there was Earth and Counter-Earth, let’s say–then the barycenter would not be inside either of them but between them.

That’s the case with Pluto and its former moon, Charon. Pluto and Charon are equal enough in mass that the barycenter of their system isn’t inside Pluto but between the two bodies and, since Charon is big enough to be a sphereoid under its own gravity, it would get counted as a planet in the new definition.

Good for Charon, but I think it’s dumb to base whether or not something is a planet on something as arbitrary whether the barycenter it’s orbiting is above or below the crust of a neighboring body. Based on that criterion, any object, no matter how much it looks like a planet–even one as massive as Jupiter–would cease to be a planet if it were pushed into orbit around a sufficiently massive neighbor.

That gets us away from a natural kinds definition, and I don’t like that. Basing whether something is a planet on what its neighbors are like is just scientifically inelegant. Planethood should be intrinsic to the planet itself, not conditional on the other members of its orbital system.

Now, I know darn well why the IAU included this condition. There’s a very specific reason: It’s to keep us from having to classify the Moon as a planet. The Moon is larger than Pluto and, if it wasn’t orbiting the Earth-Moon barycenter it would be classified as a planet. In fact, the Moon is larger than all three of the new planets–Ceres, Charon, and Xena.

Furthermore, the Moon is slightly smaller than Mercury and other moons–like Ganemede and Titan–are bigger (in radius if not mass) than Mercury, whose status as a planet very few are willing to challenge.

The IAU’s committees, though, felt that they had to include some kind of location-based criterion in their definition just to keep the Moon from being classified as a planet.

I think that’s dumb. It’s scientifically inelegant as it gets us away from a natural kinds definition.

Put another way: What a celestial body is is more important than where the celestial body is.

I’d much rather bite the bullet and say, "Guess what, folk! We’re living in a twin-planet system and always have been: The Moon is our twin planet!"

I think that would be cool, as well as more scientifically elegant.

But that’s my opinion, and others are free to hold whatever ones they want.

After all, the term "planet" is of human construction and humans together should decide what it means. I’m just advocating the most non-arbitrary definition I can think of (big enough to be a sphereoid, small enough it doesn’t fuse).

We should know within a week what course the IAU finally takes, and I’m hoping that they’ll adopt at least something like the proposed defintion (though I’d love it even more if they adopted mine instead).

I’m just jazzed about getting new planets in my lifetime.

What’s cooler than that?

If a new proposal of the International Astronomical Union is accepted, there will now be twelve planets in the solar system: Tauron, Gemenon, Scorpion, Saggitaron, Caprica . . . Oh, wait. No. Those are the twelve planets in Battlestar Galactica.

Our twelve planets will be: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, and Xena. (See! There was a TV reference in there!)

And there may be more to come. Many, many more, potentially.

I’ve been meaning to blog about the definition of what a planet is for some time, but haven’t gotten around to it. Now the IAU is about to take action on the question, so here’s a quick version:

For the last few years there has been a debate going in astronomical circles over the definition of what a planet is. This is not a new debate–the discovery of what we now consider to be asteroids led to a similar debate. When Ceres–the largest object in the asteroid belt–was discovered, it was originally considered a planet. Later, when many, many more and smaller objects were discovered in a similar orbit, the category of "asteroid" was come up with, and the debate cooled off for a while.

Then in 1930 the planet YuggothPluto was discovered, and we’ve lived culturally with the idea of Pluto being a planet for going on 80 years now.

Problems is: Pluto turned out to be a lot smaller than we originally thought. Much of the mass originally attributed to it belongs to its moonsister-planet, Charon. And we started finding other objects similar to Pluto in similar, far-out orbits in what is known as the Kuyper belt. It looked like the asteroid belt problem all over again, and some folks started advocating that Pluto be demoted from the status of planet to something else, just as Ceres was. Only the new objects wouldn’t be called asteroids but "Kuyper-belt objects" or "trans-Neptunian objects" or something like that.

The thing that finally forced the issue was the discovery in 2003 of an object known as Xena. Actually, that’s just it’s nickname, and they’ll probably get around to giving it a more serious name–especially if it’s status as a planet is accepted. Technically, it’s known as 2003 UB313 and the thing about it that forced the definition of a planet debate is that it’s larger than Pluto.

As long as Pluto was the biggest of the things we knew about in the outer solar system, we could kinda let its status as a planet slide, but after we went and found something bigger, we needed to either classify it as a planet too or–if we didn’t want to do that–to vote Pluto out of the planet club. (Sorry, Pluto. That’s the way reality television works!) Of course, some folks speculated about grandfathering Pluto as a planet for sentimental reasons, while denying larger objects, but that’s excessively inelegant.

So the IAU has been debating what to do about defining a planet for some time, and a number of proposals have been developed.

CHECK THEM OUT.

The executive committee has now whittled it down to one proposed definition, which is as follows:

“A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.”

Under that definition, at least three bodies in the solar system would get counted as planets:

First, Ceres would get re-promoted to the status of planet. (Welcome back Ceres! Our reality TV show let’s people to get voted back in to the club! Try not to get any demerits this time!)

Second, Pluto’s "moon" Charon would get promoted to planet, too, since it’s mass relatie to Pluto is so large that the point the two orbit is not within either body but between them, meaning that neither orbits the other but they both orbit a common point. (I’m hinky about this one; more on that later.)

Third, Xena (as the largest of these three objects) would get planet status–and probably a more serious name, though I’d love to see the TV name become official.

And there might be more!

Under the new definition we’d have to further study other objects in the solar system to see if they, too, met the criteria about having enough gravity to create a stable shape for themselves, given their composition.

The proposal has been recommended by the executive committee of the IAU to the full body, which is currently meeting in Prague, and a vote is likely to be taken on it this week or next.

If the IAU accepts the proposal (as seems likely) then we’ll have to get used to living in a somewhat more accomodating planet club than we have been to date.

Oh, and non-scholar Zecharian Sitchin will have to find a new title for his dumb book The 12th Planet.

I’ll offer my own thoughts on the proposed definition of what a planet is in another post, but I wanted to use this one as a backgrounder to the current debate.

MORE.

AND MORE FROM THE IAU ITSELF.

Michelle here!

If you thought that marriage didn’t cure depression, think again! If you’re depressed, you should get married. If you thought that you should be reasonably content with yourself before getting married, think again! If you’re content with yourself, you should say single. If you believe The Latest Research anyway….

"’We actually found the opposite of what we expected,’ said Adrianne Frech, a PhD sociology student at Ohio State University who conducted the study with Kristi Williams, an assistant professor of sociology.

"They expected to find that one spouse’s depression weighed too much on the marriage, but ‘just mattering to someone else can help alleviate symptoms of depression,’ Frech said."

And on the flip side….

"On the other hand, if you’re not depressed, marriage could have the opposite effect, Frech said.

"People who were happy before getting married and end up in a marriage plagued by distance or conflict — qualities associated with a depressed spouse — might be better off single."

GET THE STORY.

So, the only people depressed people should marry are other depressed people? While I certainly can’t blame content people for shying away from marriage with a depressed person — something I think is best categorized as Common Sense — does it really make sense to imply that a depressed person should form an intimate relationship with someone else who is depressed? Might it not be better for both of them to receive the proper treatment before contemplating marriage to anybody?

But then what do I know? I don’t even play a doctor on TV.

A piece back I introduced y’all to the Vampire Squid From Hell.

Well, it turns out that the animal kingdom ain’t the only place that has morbidly-named, fascinating creatures in it. The plant kingdom does, too!

What you’re looking at here (left) is the blossom of a parasitic plant known as the "corpse flower."

It’s native to Indonesia and surrounding region, and it is so-named because . . .  well . . . because it smells like decaying meat.

The reason–apparently–is that the corpse flower wants to attract flies and other insects that like the smell of decaying meat and who then help with things like pollination.

The genus to which the corpse flower belongs contains a number of related species and include the largest known flowers in the world, with a bloom a meter wide and weighing up to 24 lbs (11 kg).

Recently a corpse flower bloomed (they only do that every few years) at a greenhouse in Virginia, causing not only a lot of hungry flies to be attracted but a lot of curious humans as well.

The Virginia Tech folks hosing the corpse flower even set up a web cam so curious humans could catch a glimpse (if not a whiff) of it at a distance.

They also posted a lot of other pictures of the corpse flower and its development, one of which I’ve included here (right).

All I can say is . . . I don’t want anyone laying one of these things by my bed at night, and not just because of the smell.

GET THE STORY.

LEARN MORE.

ABOUT THE WORLD’S BIGGEST FLOWER.

SEE THE PICTURES ON THE VIRGINIA TECH SITE.

Earlier today I commented on the hypothetical "Green Beard Effect" that may lead organisms to behave favorably toward other organisms displaying the same trait or traits.

The "Hey, we’re the same" instinct–whether it specifically captures what Dawkins et al. have in mind with the Green Beard Effect–is definitely something present in higher species (and many lower ones as well).

But there’s also the contrary impulse–what we might call the "Vive la difference" instinct–which causes us to favorably regard others specifically because their traits are different than ours.

Perhaps the most obvious example of this is the fact that we find the opposite sex attractive. If we didn’t, mating and reproduction wouldn’t occur and the species would die out. We are therefore genetically programmed to find those with the opposite sexual characteristics to be sexually attractive.

This instinct manifests in other ways, too.

For example, all human societies have an incest taboo. The nature of the taboo (i.e., exactly who you can’t marry) varies from culture to culture, but there is always an incest taboo of some kind. It is a human universal and thus seems to be based in our genetics.

The reasons for the incest taboo are debated.

One of the most common explanations you hear for why the incest taboo exists is that, if it didn’t and if a lot of incest went on as a result, it would harm the population by causing children to have birth defects due to inbreeding.

Maybe.

If that’s the reason for the taboo then it isn’t a conscious one. The ancients, who didn’t have access to modern science, didn’t seem to justify the prohibition of incest on those grounds.

St. Thomas Aquinas, for example, says nothing about it in his discussion of why incest is wrong.

I did some research a number of years ago on the subject (as part of answering the regular question "Where did Cain get his wife?") and found individuals arguing that the birth defects resulting from incest are not as common as is commonly supposed and that, if really severe, survival-affecting ones appear in a population, they’ll die out (or cause the population as a whole to die out). Also, until very recently, many humans lived in small, fairly isolated communities and didn’t have a lot of opportunity for marrying outside their neighbors, with the result that there has been a lot more inbreeding (if not incest) in human history than is often supposed.

Then there are people who argue the opposite of all this.

I don’t know which side is correct, but I mention the former position just to call attention to its existence, for you seldom hear it articulated.

My own suspicion is that we have the incest taboo because it’s just in us genetically and we have historically and are presently trying to come up with intellectual justifications for why something that we instinctively feel to be wrong is actually wrong.

In other words, it’s just part of the law of God written on the hearts of men.

God’s laws are for our good, and so I’m sure that there is a benefit–or several benefits–that come to mankind as a result of the incest taboo. One of them may be that it helps to prevent birth defects, but I’m not sure that there aren’t other, greater reasons.

In general, the incest taboo has the effect of bringing new genes into a family line and thus increasing its genetic diversity. Genetic diversity will allow it to withstand hardships better since there is a greater likelihood that some in it will be able to better weather the latest plague, famine, forced migration, or what have you.

A prohibition on inbreeding also helps broaden social ties, which result in an individual having greater social resources to draw upon. Of all the arguments that St. Thomas makes against incest, the one that strikes me as having the most force is this:

[Incest] would hinder a man from having many friends: since through a man taking a stranger to wife, all his wife’s relations are united to him by a special kind of friendship, as though they were of the same blood as himself. Wherefore Augustine says (De Civ. Dei xv, 16): "The demands of charity are most perfectly satisfied by men uniting together in the bonds that the various ties of friendship require, so that they may live together in a useful and becoming amity; nor should one man have many relationships in one, but each should have one."

If people marry outside their own families then the social fabric is strengthened and the society does better as a result.

Whatever the benefits God intends us to have as a result of the incest taboo–whether it’s avoidance of birth defects, increase of genetic diversity, stronger social ties, or a combination of these or something else entirely–we do have an aversion to incest that appears in all societies and that is likely genetic.

It would thus seem to involve a preference (at least in terms of mating) for those who are different from us in that they aren’t too closely related.

But the preferential option of those who are different goes beyond a preference for the opposite sex and beyond a preference for those who aren’t too closely related to us. There is some, though weaker, evidence that there is at least something of a drive in us toward exogamy, or marriage outside our own group.

The fact that most people marry within their own group and have done so historically suggests that this is a weak desire, but there is still an attraction to the exotic. People from other cultures can seem mysterious and romantic or their accents may be perceived as sexy.

Or not.

Like I said, it’s a weak desire in humans or people would have gone further afield to find mates than they historically did most of the time.

Nevertheless, we’re attracted not only by similarities but also by differences.

Last weekend when I was doing my first post on Pirates of the Caribbean (go see the movie if you haven’t), I was doing some research on Wikipedia about the origin of the phrase "Dead Man’s Chest." I knew it was from a sea shanty, but I didn’t remember the full lyrics of it.

TURNS OUT IT APPEARS TO BE FROM A SHANTY MADE UP BY ROBERT LOUIS STEPHENSON IN TREASURE ISLAND.

Though it may be based on a real-life event involving Blackbeard the pirate.

That got me to thinking: There have been quite a number of pirates known by the color of their beards, but I couldn’t remember which of them were real and which were fictional. (I’m not much of a pirate expert, I’m afraid.)

I remembered hearing about "Bluebeard," for example (I think in a Scooby-Doo cartoon I saw as a kid or something), but I couldn’t remember if Bluebeard was real or fictional. So I Wikipediaed him.

Turns out he was a fictional aristocrat rather than a pirate.

I also remembered that there was a movie about pirates called Yellowbeard (though I never saw that and suspect I wouldn’t like it).

And there’s a comicbook character called Redbeard.

"Just how far does this go?" I wondered. "There can’t be many more pirate characters with colored facial hair designations."

So I typed in "greenbeard" and, sure enough, there was no such pirate.

BUT THERE WAS A SCIENTIFIC CONCEPT KNOWN AS "THE GREEN BEARD EFFECT."

The basic idea is that there might be sets of genes that cause an organism to have a particular characteristic and to be altruistically disposed to other organisms that share that characteristic, even if they are otherwise unrelated. The gene set would thus promote its own replication apart from a close family connection.

For example, suppose that there were a gene set that caused certain humans to have green beards. Such people might form a kind of mutual defense league.

Supposedly they’ve actually documented the green beard effect in, of all things, red fire ants.

I don’t know if they need to look that far, though.

I don’t want to give away any secrets of the Red Headed League, but I’ve noticed that women who are or who used to be red heads often seek to engage me in what I can only describe as "red-head mutual bonding conversations" (e.g., complimenting my hair color, observing that it’s a darker red on the sides of my head than on the top, telling me about their hair color and things they may have done to maintain or accentuate it). Guys don’t do this, but then guys don’t generally talk much about their hair color in my experience (except to complain about gray).

Being a guy, I don’t have much to say in such conversations, but I’ve been struck by the number of times present and former red heads start them with me, and there’s a definite, positive "Hey, we’re two of a kind" vibe that comes across, even from women old enough to be my grandmother and whose hair is now white.

I also suspect that this effect–if I understand it correctly–is all over the place in biology, even across species.

For example, it’s often been remarked that the reason we find puppies and kittens so cute is that they, like our own offspring, have big heads and big eyes compared to their mature forms. Mammals that have big heads and big eyes in infancy get perceived by us as cute and we want to take care of them, which promotes their survival. They trigger the parenting instinct in us.

There thus may be a set of genes that produce the quality of having a big head and big eyes in infancy and that foster altruism toward those organisms that have this quality, even in other species.