Sun, Earth, Moon, Earthrise, “Terra”

4.56 billion years ago

The Hadean eon begins with the origin of the Earth 4.56 Gya.

Take a look at the Moon tonight. It’s waxing, just a few days past the new moon. When the moon is full you can cover it with your thumb. 4.56 billion years ago the new moon was ruddy with volcanic activity even on its dark side. The Moon seen from Earth was 16 times wider, covering 250 times more sky, and 250 times brighter when full. That is what you would have seen just after Earth acquired a surface you could stand on, although you would have needed an oxygen mask. And watch out for massive meteorites, still falling frequently, and volcanism.

Chance events late in the history of planet formation played a huge role in shaping the solar system, including the collision with the planet Theia (named after the Greek goddess of the Moon) that gave Earth her outsized satellite. (At least that’s been the dominant theory. See here for current debates.) Life might have developed very differently – there might be no intelligent life — without the Moon’s influence on tides and on Earth’s axis.

Here’s what Earth and Moon look like today: the famous picture of Earthrise, taken December 24, 1968, by William Anders abroad Apollo 8.earthrise copy

In 1969, the Brazilian singer Caetano Veloso was imprisoned by Brazil’s military dictatorship. He was expelled from the country and lived in exile until 1972. In prison he saw a picture of the Earth from space and wrote this song, “Terra” (Earth).

TerraQuando eu me encontrava preso, na cela de uma cadeia 
Foi que eu vi pela primeira vez, as tais fotografias 
Em que apareces inteira, porém lá não estava nua 
E sim coberta de nuvens
Terra, terra, Por mais distante o errante navegante Quem jamais te esqueceria?

Ninguém supõe a morena, dentro da estrela azulada
. Na vertigem do cinema, mando um abraço pra ti 
Pequenina como se eu fosse o saudoso poeta 
E fosses a Paraíba
Terra, terra, 
Por mais distânte o errante navegante Quem jamais te esqueceria

Eu estou apaixonado, por uma menina terra,
 Signo de elemento terra. Do mar se diz terra à vista 
Terra para o pé firmeza, terra para a mão carícia
 Outros astros lhe são guia
Terra, terra,
 Por mais distânte o errante navegante Quem jamais te esqueceria

Eu sou um leão de fogo, sem ti me consumiria
 A mim mesmo eternamente, e de nada valeria 
Acontecer de eu ser gente. e gente é outra alegria 
Diferente das estrelas
Terra, terra,
 Por mais distânte o errante navegante Quem jamais te esqueceria

De onde nem tempo e nem espaço, que a força te de coragem
 Pra gente te dar carinho, durante toda a viagem 
Que realizas do nada, através do qual carregas 
O nome da tua carne
Terra, terra, 
Por mais distânte o errante navegante Quem jamais te esqueceria
Terra, terra, 
Por mais distânte o errante navegante Quem jamais te esqueceria
Terra, terra,
 Por mais distânte o errante navegante Quem jamais te esqueceria?

Na sacadas do sobrado, Da eterna São Salvador 
Há lembranças de donzelas, do tempo do Imperador
 Tudo, tudo na Bahia faz a gente querer bem
A Bahia tem um jeito
Terra, terra,
 Por mais distante o errante navegante 
Quem jamais te esqueceria. Terra

EarthWhen I found myself arrested
 In a prison cell
, That’s when I first saw
 Those famous pictures
 In which you appear entire, 
However you were not naked 
But covered by clouds.
Earth! Earth!
 However distant 
The wandering navigator 
Who could ever forget you?

Nobody thinks of the brunette
 Inside the bluish star. 
In the vertigo of the movie
 I send you an embrace, 
Little one – as if I were
 the homesick poet 
And you were the Paraíba
Earth! Earth!
 However distant 
The wandering navigator 
Who could ever forget you?

I’m just in love 
With an earth girl, 
Sign of the element “Earth.” 
From the sea is said “Land in sight.” 
Earth to the foot: solidity. 
Earth to the hand: a caress.
 Other stars are guides for you
Earth! Earth! 
However distant 
The wandering navigator 
Who could ever forget you?

I am a lion of fire
 Without you 
I would burn myself up eternally 
And it would be worth nothing, 
The fact of my being human. 
And human is another joy 
Different than the stars’
Earth! Earth! 
However distant 
The wandering navigator 
Who could ever forget you?

From where there’s neither time nor space 
May the force send courage 
For us to treat you tenderly
 During all the journey 
That you carry out through nothing
 Through which you bear
 The name of your flesh
Earth! Earth!
 However distant 
The wandering navigator 
Who could ever forget you?
Earth! Earth! 
However distant
 The wandering navigator
 Who could ever forget you?
Earth! Earth! 
However distant
 The wandering navigator
Who could ever forget you?

In the townhouses’ terraces 
Of eternal Salvador 
There are reminders of maidens 
From the time of the Emperor 
Everything, everything in Bahia
 Makes us fond 
Bahia has such a way.
Earth! Earth! 
However distant
 The wandering navigator
 Who could ever forget you? 


Rare Earth

4.75-4.50 billion years ago

A big day on Logarithmic History: the origin of our Solar System including planet Earth. First a note on what’s odd about our planetary system.

Two preceding posts wrestled with the Fermi Paradox: If the universe is full of advanced civilizations, why haven’t we seen any sign of them so far? One answer to the paradox might be that our solar system is wildly unusual, so that abodes for the evolution of complex life are rare. We can finally start to address this matter with some real evidence. According to the NASA exoplanet archive, we’ve now discovered 3587 exoplanets (planets outside our solar system; up from 3440 last year at this date), with many more unconfirmed candidates. This is enough to do some statistics, and indications are that our solar system might indeed be out of the ordinary.


Exoplanets smaller than Jupiter are overwhelmingly closer, mostly a lot closer, to their primary stars than Earth is to the Sun. And the same models of planet formation that have done a pretty good job predicting some of the wild variation we see in other systems – “Hot Jupiters” orbiting closer to their primaries than Mercury, “Super Earths” in between Earth and gas giants in size – don’t readily generate systems that look much like ours. One model that does seem to do a good job with our solar system involves something special, a Grand Tack, where Jupiter and Saturn are caught in an orbital resonance that carries them into the inner solar system and back out, shaking up inner-system planet formation in the process. Wild stuff, but the latest model is even wilder: at the beginning of planet formation, there may have been a generation of Super Earths in the inner solar system. The Grand Tack of Jupiter and Saturn would have sent these planets colliding into one another. The Super-Earths and most of the debris of these collisions would have fallen into the sun, but what the debris left would then have condensed into the unusual inner planets we know, Mercury, Venus, Earth, Mars. And Theia. (Theia? you ask. See the next post).

If this model holds up, the formation of our solar system takes on some of the flavor of mythology. This isn’t quite the old story about Chronos slaying Ouranos, and Zeus slaying Chronos. Instead, in the new story, two giants, Jupiter and Saturn, travel closer to the sun and set a generation of Titans – their like will not be there again – to fighting and destroying one another. Jupiter and Saturn depart, and a new generation is spawned from the wreckage. An unlikely sequence of events, but then our planet could be a very unlikely place. And all the more special for that.

Where is everybody? Maybe we’re (some of) the first.

5.31-5.03 billion years ago

A followup to yesterday’s post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible.

On its own, it’s not clear this would have prevented intelligent life from arising long ago. The Sun has a high “metallicity” (concentration of heavy elements), but there are stars in the Milky Way older than the Sun with higher metallicities. But metallicity could combine with GRBs (below): toward the center of the galaxy there are more heavy elements but also more GRBs.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out tweets for January 11.) They are probably supernovas or even larger explosions with one pole of the exploding star pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere off Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.


Where is everybody?

5.62 – 5.32 billion years ago

Today in Logarithmic History, January 17, covers a period beginning over a billion years before the origin of our solar system. Back then, stars were forming at a fast clip in the Milky Way and other spiral galaxies. So let’s suppose… Suppose one of those older stars resembled the Sun, and had a planet like Earth orbiting around it – call it Urth. And suppose life originated on Urth more or less as on Earth and followed more or less the same evolutionary path. With this head start, intelligent life could have evolved a billion years ago, and today there could be intelligent Urthians (or their robot descendants) a billion years ahead of us.

There’s an urban legend that says that Einstein called compound interest the strongest force in the universe. Einstein didn’t actually quite say this, but it’s not a crazy thing to say. For example, consider how compound interest works, backward, on our Logarithmic History calendar. December 30 covers a period 5.46% longer than December 31, December 29 is 11.2% longer (because 1.0546 * 1.0546 = 1.112), and so on. At this rate of compounding we wind up with January 1 covering 754 million years. The same math implies that if we invested 1 dollar at 5.46% interest, compounded annually, then after 364 years we’d have 754 million dollars.

With even the slightest compound rate of increase, a billion year old Elder Race would have plenty of time to fill up a galaxy, and undertake huge projects like dismantling planets to capture more of their suns’ energy. Which raises the question, posed by Enrico Fermi in 1950: “Where is everybody?” There are more than 100 billion stars in our galaxies, more than 100 billion galaxies in the visible universe (actually, according to recent estimates, the number may be more than  1 trillion). If there are huge numbers of billion year old Elder Races around, why hasn’t at least one of them taken the exponential road and made themselves conspicuous?

There’s a large literature on the Fermi paradox. One possible explanation is that we’re one of the first intelligent species to evolve because the universe was somehow less suitable for the evolution of complex life before now. I’ll take that one up tomorrow.

Physical attractiveness and the theory of sexual selection

As we wait for our solar system to appear (coming up soon, January 20), here again is a break in the proper order of things on Logarithmic History, introducing some of my own work, in this case a pdf of a book from a while back. The book, Physical Attractiveness and the Theory of Sexual Selection: Results from Five Populations (1996), based on my PhD thesis and several articles, presents results of research on standards of physical attractiveness in five populations: Americans, Brazilians, Russians, Ache Indians (Paraguay) and Hiwi Indians (Venezuela). (Data for the Hiwi were collected by my adviser Kim Hill).

Looking back, I would say that the book, and the associated research, was a pioneering effort. When it came out there was already a significant body of work in social psychology on criteria and consequences of attractiveness. But the research in the book was some of the first to get truly cross-cultural, including data from isolated former hunter-gatherers. And it was some of the earliest work on attractiveness to try and connect the psychology literature with the theory of sexual selection, and with research on sexual selection in non-humans.

There are things I would change if I were doing a rewrite. There are occasional plain mistakes – minor mistranslations, and so on. And the statistical analysis could be improved on. For example, when it comes to the data on race and somatic prejudice in Brazil, I do a better analysis in this book chapter.

In the main however, the book holds up fairly well. There’s a lot of concern in the human sciences these days about whether research results are replicable and reliable. From this perspective it’s reassuring that some major findings of the book – that men find especially feminine/neotenous women’s faces especially attractive, that faces closer to the population average are seen as more attractive – are supported by later research. (On the flip side, I was one of the first people to look for a connection between fluctuating asymmetry and attractiveness in any species. I found no significant correlation.)

On a philosophical note: on December 18 last year, I reposted some reflections on the evolution of human sexuality. The Schopenhauer quotation from that post (my translation) first appeared in Physical Attractiveness and the Theory of Sexual Selection, a book in which “I have striven not to laugh at human actions, not to weep at them, nor to hate them, but to understand them” (Baruch Spinoza).

Evolution and broken symmetries

8.33-7.88 billion years ago.

No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?

Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification.

However, people sometimes talk about evolution that doesn’t involve descent with modification, in contexts that have nothing much to do with biological evolution – cosmic evolution or stellar evolution in the history of the universe, for example, or mineral evolution in the history of the earth. Another Victorian writer, the sociologist and philosopher Herbert Spencer, offered a definition of evolution that might cover these cases.

Evolution is an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity.

It’s easy to make fun of this definition. It’s the sort of abstract word pile that style manuals tell you to avoid, and that gives sociology a bad name. For that matter, it’s easy to make fun of Herbert Spencer. He may be some of the inspiration for the character of Mr. Casaubon, the dried up, impotent pedant in George Eliot’s “Middlemarch.” (Spencer probably turned down a chance to marry George Eliot = Mary Ann Evans. You should be careful about offending a writer.) But it may be that Spencer was groping toward the important modern concepts of symmetry and symmetry breaking.

A simple example: imagine you’re holding a bicycle exactly upright. The bicycle is pretty much bilaterally (mirror image) symmetrical. (OK, not really, the gears are on the right side, so it’s not a perfect mirror image. But just pretend …) Now let go of the bike. It will fall to one side or the other. The symmetry is broken, and you need one extra “bit” of information to tell you which side the bicycle is on.

Symmetry breaking is a fundamental concept in physics. In the very early history of the universe, the four forces of nature — gravitational, strong, weak, and electromagnetic – were united, but then as the universe cooled, one by one, these forces broke the symmetry and turned into separate forces. More symmetry breaking generated elementary particles, and nuclei, and atoms. When atoms first formed, they were distributed symmetrically through the universe as a diffuse gas. But gravitation pulled atoms and other particles together into clumps, leaving other parts of space emptier, and the spatial symmetry was broken (a “translational” symmetry in this case).

Symmetry breaking will keep showing up throughout the history of the universe. Consider sexual reproduction. A simple early form of sex involved two equal sized gametes (sex cells) joining to produce a new organism. Some species still do it this way. But more commonly the symmetry is broken – some organs or organisms produce little gametes that move around easily (sperm or pollen), others produce big gametes that don’t move around so easily (eggs or ovules). We call the first sort of organs or organisms male and the second sort female. Sex in most multi-cellular organisms is a broken symmetry. This broken symmetry will go on to have a dramatic consequences for human social evolution. It entails, for example, that patrilineages can expand their size much more rapidly than matrilineages.

Or consider the rise of political stratification, the move from small-scale societies where “every man is a chief” to large-scale societies of chiefs and commoners, rulers and ruled. Another broken symmetry. It may be more or less an accident (good or bad luck, Game of Thrones style) who ends up being king, but it’s not an accident that somebody is, past a certain social scale.

We don’t attach much moral significance to broken symmetries where the physical world is concerned. You’re being way too sensitive if you feel sorry for the poor weak nuclear force that missed its chance to be the strong nuclear force, or for the dwarf galaxies that got cruelly tossed around and cannibalized by the Milky Way. Broken symmetries in social life – males and females, kings and commoners – are another matter …

Kin selection and ethnic group selection

Sometimes I interrupt the normal day-by-day progression of Logarithmic History to cover my own work. Here I introduce a just-published paper, “Kin selection and ethnic group selection.” It’s about what, if anything, ethnicity has in common with kinship – evolutionarily speaking that is, on the assumption that human psychology has been shaped by natural selection. The paper doesn’t have anything to do with galaxy formation or nucleosynthesis, recent topics on the blog, but it would have been a good fit on August 5 last year, when I wrote about cultural group selection, population genetics, and prehistory, or December 15, when I wrote about nationalism in Europe at the end of the Cold War.

The paper itself is behind a paywall, but here’s a link to an earlier uncorrected, unpublished draft.

As a starting point, take the concept of ethnic nepotism. If you look up the term on the web, one thing you’ll find is an array of sources arguing that ethnicity is kinship on a large scale, and that the theory of kin selection, developed in evolutionary biology to explain altruism, cooperation, and conflict in families, is also a key to understanding such things at the level of ethnic groups. In the paper, I cite academic publications that take this position, including some from my late colleague at the University of Utah, Henry Harpending. And here is a non-academic link.

But you’ll also find people arguing the opposite, that ethnicity can’t be equated with kinship, at least as far as the theory of kin selection is concerned. Again I cite academic publications in the paper, and here, here, and here are some non-academic links.

The nay-sayers win the first round of the argument. I cover this in the first part of the paper. The theory of kin selection is concerned with r, the coefficient of relatedness, the expected number of genes that one organism shares with another as a result of common descent. Natural selection favors altruism between family members in proportion to their r’s, as a gene’s way of making more genes. So we’re told by William Hamilton, the biologist who figured this out. As it turns out, we can calculate r values not just for families, but for large groups – nations, continent-scale races. Does this mean we can plug these r’s into the standard formula and predict altruism between ethnic group members accordingly? No, because we’re now violating something called the weak selection assumption (see the paper for details). A physics analogy: at Earth’s surface, a falling object accelerates at a constant 9.8 meters per second per second. So we’re told by Galileo. This works for heavy objects over short distances. But we run into problems if we try to apply this law to lighter objects and longer distances without allowing for air resistance. Assuming weak selection in the theory of kin selection is like assuming no air resistance in physics, a simplifying assumption that can get us in trouble.

Eppur … even if ethnicity can’t simply be equated with kinship, it’s still theoretically possible to rescue the idea of ethnic nepotism, with the help of two further principles.

Socially enforced altruism. Suppose you decide, on your own, to help somebody at some cost to yourself. (If we’re thinking about evolution, we’ll want to count benefits and costs as fitness increments and decrements.) This is an instance of individual altruism. Discussions of kin selection commonly begin and often end here. But now imagine that you are part of a group that decides collectively to help another group. You and your fellow villagers, say, vote to tax yourselves to help a neighboring village recover from a flood; you don’t expect them to pay you back. This is socially enforced altruism. It’s not altruism at the individual level – you pay the tax to avoid a penalty – but it’s altruism at the village level – y’all could have kept the money for yourselves. In an earlier paper, I analyzed a variant on this, a reputation-based system where you help the needy not so much out of pure kindness, but to get the benefits that go with having a good reputation. I showed how the social enforcement of charity via reputation can amplify altruism toward distant kin. (Here’s the article, and a blog post about it, Beating Hamilton’s Rule, and an earlier article, Group nepotism and human kinship, and another post on the Brothers Karamazov Game, a simple three-person version of group nepotism.)

Ethnic group relatedness. The earlier paper was concerned with socially enforced altruism at the scale of local kin groups. Socially enforced altruism might also work at the level of ethnic groups. In this case, however, genetic similarity among segments of an ethnic group may reflect something other than just shared descent. In this case, two segments of an ethnic group may be genetically similar because they have shared a common culture for some time, resulting in similar selection pressures on genes contributing to the maintenance of that cultural regime. The basic principle behind kin selection can still operate here – you (or y’all; see above) help others because they share your genes, even if they can’t pay you back. But the expected number of shared genes – the ethnic coefficient of relatedness – no longer tracks the standard r’s based on genealogy or genetic similarity over the genome as a whole.

So ethnic group nepotism resulting from ethnic group selection* is a theoretical possibility, and I lay out the theory in the middle part of the paper. Whether it actually occurs I consider in the last part of the paper, which reviews some population genetics and political psychology.**


* Depending on how we define our terms, selection for socially enforced altruism may or may not count as group selection, but either way the usual objections to group selection for pure altruism don’t hold here.

** The social science literature on ethnicity and nationalism, including Conor, Gat, and Horowitz, is a topic for another day.