Tag Archives: evolution

When you were a tadpole and I was a fish

1.17-1.11 billion years ago

The Boring Billion rolls on. The atmosphere is one percent oxygen or so thanks to photosynthetic bacteria and algae. The ocean still largely anoxic and thick with sulfates and sulfate-eating bacteria. Eukaryotes have been around for a while, and are diversified, although still all single celled (as far as we know).

Sexual reproduction begins with eukaryotes, and by now some groups are presumably differentiated into male and female. For those of you who are not bdelloid rotifiers, here’s a poem for Valentine’s Day, by the biologist Langdon Smith. Martin Gardner has a nice account of the poem, in his book “When you were a tadpole and I was a fish,” and here’s a great video of the poem spoken by Jean Shepherd.

Evolution
By Langdon Smith (1858-1908)

When you were a tadpole and I was a fish
In the Paleozoic time,
And side by side on the ebbing tide
We sprawled through the ooze and slime,
Or skittered with many a caudal flip
Through the depths of the Cambrian fen,
My heart was rife with the joy of life,
For I loved you even then.

Mindless we lived and mindless we loved
And mindless at last we died;
And deep in the rift of the Caradoc drift
We slumbered side by side.
The world turned on in the lathe of time,
The hot lands heaved amain,
Till we caught our breath from the womb of death
And crept into life again.

We were amphibians, scaled and tailed,
And drab as a dead man’s hand;
We coiled at ease ‘neath the dripping trees
Or trailed through the mud and sand.
Croaking and blind, with our three-clawed feet
Writing a language dumb,
With never a spark in the empty dark
To hint at a life to come.

Yet happy we lived and happy we loved,
And happy we died once more;
Our forms were rolled in the clinging mold
Of a Neocomian shore.
The eons came and the eons fled
And the sleep that wrapped us fast
Was riven away in a newer day
And the night of death was passed.

Then light and swift through the jungle trees
We swung in our airy flights,
Or breathed in the balms of the fronded palms
In the hush of the moonless nights;
And oh! what beautiful years were there
When our hearts clung each to each;
When life was filled and our senses thrilled
In the first faint dawn of speech.

Thus life by life and love by love
We passed through the cycles strange,
And breath by breath and death by death
We followed the chain of change.
Till there came a time in the law of life
When over the nursing sod
The shadows broke and the soul awoke
In a strange, dim dream of God.

I was thewed like an Auroch bull
And tusked like the great cave bear;
And you, my sweet, from head to feet
Were gowned in your glorious hair.
Deep in the gloom of a fireless cave,
When the night fell o’er the plain
And the moon hung red o’er the river bed
We mumbled the bones of the slain.

I flaked a flint to a cutting edge
And shaped it with brutish craft;
I broke a shank from the woodland lank
And fitted it, head and haft;
Then I hid me close to the reedy tarn,
Where the mammoth came to drink;
Through the brawn and bone I drove the stone
And slew him upon the brink.

Loud I howled through the moonlit wastes,
Loud answered our kith and kin;
From west to east to the crimson feast
The clan came tramping in.
O’er joint and gristle and padded hoof
We fought and clawed and tore,
And cheek by jowl with many a growl
We talked the marvel o’er.

I carved that fight on a reindeer bone
With rude and hairy hand;
I pictured his fall on the cavern wall
That men might understand.
For we lived by blood and the right of might
Ere human laws were drawn,
And the age of sin did not begin
Til our brutal tush was gone.

And that was a million years ago
In a time that no man knows;
Yet here tonight in the mellow light
We sit at Delmonico’s.
Your eyes are deep as the Devon springs,
Your hair is dark as jet,
Your years are few, your life is new,
Your soul untried, and yet –

Our trail is on the Kimmeridge clay
And the scarp of the Purbeck flags;
We have left our bones in the Bagshot stones
And deep in the Coralline crags;
Our love is old, our lives are old,
And death shall come amain;
Should it come today, what man may say
We shall not live again?

God wrought our souls from the Tremadoc beds
And furnish’d them wings to fly;
He sowed our spawn in the world’s dim dawn,
And I know that it shall not die,
Though cities have sprung above the graves
Where the crook-bone men made war
And the ox-wain creaks o’er the buried caves
Where the mummied mammoths are.

Then as we linger at luncheon here
O’er many a dainty dish,
Let us drink anew to the time when you
Were a tadpole and I was a fish.

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Between Darwin and Saint Valentine

Yesterday was Darwin’s birthday (and Lincoln’s). Tomorrow is Valentine’s Day. Here’s a post appropriate for either day.

Imagine sex worked like this:

You’ve been feeling bad lately, getting sick a lot. You’re not at your best. You find someone who seems to be in better shape. One thing leads to another and you wind up acquiring body fluids from the other party – and picking up some new genes from them. The new genes help a lot in fighting off infection. You’re feeling better now.

Reproduction? That’s another matter, nothing directly to do with sex. When you reproduce, your offspring will carry all the genes you happen to have at the moment.

Also, I forgot to mention that you’re neither male or female – the gene exchange could have gone in the other direction if you’d both been in the mood. And your partner in the adventure above might not even have been the same species as you. (Just what counts as a species here isn’t well-defined.)

This is more or less how bacteria work out sex. (Joshua Lederberg got the Nobel Prize for figuring this out.) Eukaryotes (you’re one of them) mostly do it differently, combining sex and reproduction. It’s the story you learned in high school about passing on half your genes to a gamete (sex cell), which joins with another gamete to make a new organism.

Most eukaryotes also have two sexes. The best theory we have about why that got started goes like this: Most of the DNA in a eukaryote cell is in the nucleus. But a small fraction is in the mitochondria, little powerhouses outside the nucleus that started out as bacteria, and got domesticated. Imagine that two gametes join together, and combine two sets of mitochondria. There’s a potential conflict here. Suppose your mitochondria have a mutation that lets them clobber your partner’s mitochondria. This is good (evolutionarily speaking) for the winning mitochondria, but very likely to be bad for the cell as a whole. Better for the cell as a whole is if one gamete, acting on instructions from the nucleus, preemptively clobbers all their own mitochondria, so that all the mitochondria come from just the other gamete. This is the beginning of what will eventually lead to a distinction between sperm and eggs, pollen and ovules, male and female. Which means you got all your mitochondrial DNA from your mom, something that will turn out to be important when we look later in the year at geneticists unraveling human prehistory. This is also an example of how selection at one level (within cells) can conflict with selection at another level (between cells). We’ll see such multilevel selection again and again, for example in the evolution of complex human societies.

Sex has to be highly advantageous, although we’re not sure exactly what the advantage is. When eukaryote species give it up, they don’t seem to last long. Dandelions reproduce asexually: based on what we see in other organisms, they probably won’t be around for long, evolutionarily speaking. There’s one mysterious exception, tiny animals called bdelloid rotifers which have been reproducing asexually for tens of millions of years . For readers who are not bdelloid rotifers: Happy Valentine’s Day tomorrow! We’ll have an appropriate evolutionary post up tomorrow

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 …

Progress

2017

Both simple and complex types of language of an indefinite number of varieties may be found spoken at any desired level of cultural advance. When it comes to linguistic form, Plato walks with the Macedonian swineherd, Confucius with the head-hunting savage of Assam.

Edward Sapir. Language: An Introduction to the Study of Speech

The institutions of men are as distinctly stratified as the earth on which he lives. They succeed each other in series substantially uniform over the globe, independent of what seem the comparatively superficial differences of race and language, but shaped by similar human nature acting through successively changed conditions in savage, barbaric, and civilized life. … Few would dispute that the following … are arranged rightly in order of culture: Australian, Tahitian, Aztec, Chinese, Italian.

Edward Burnett Tylor, Primitive Culture

These quotations capture two aspects of cultural evolution. Cultures (including languages) diverge and diversify over time. But cultures can also be ranked from simple to complex, from small scale to large scale, and complexity tends to increase over time. A recent publication provides quantitative evidence for this second, unilinear aspect of cultural evolution. The publication is the product of project Seshat (named after the Egyptian goddess of wisdom, alleged inventor of writing), which has been building up a massive databank of global history. (You can follow them on Twitter here.) The authors of the study (54 of them!) find that a single dimension of social scale/complexity accounts for a large fraction of cultural variation over space and time, and that the correlates of social scale are much the same in different world regions – Tylor vindicated.*

Turning from cultural to biological evolution we find the same two phenomena, both diversification over time, and increasing complexity and improved design. But in the biological case, it is diversification that is relatively more conspicuous. Presumably this reflects that fact that in biology, adaptive organization is found mostly at the level of organisms (or, less often, at the level of superorganisms, like insect colonies, or mutualistic associations). A great diversity of organisms can be found in any ecosystem, adapted to a diversity of niches. They are mostly not in direct competition and may be hard to rank along a single scala naturae. In cultural evolution, by contrast, adaptive organization is commonly found not just at the individual level, but at the level of political communities – tribes, chiefdoms, states – which typically claim possession of a piece of territory. Success or failure at holding territory provides a metric for comparing societies, which usually (not always) favors the more complex.

So both the history of humanity, and the evolution of life on earth, and are, in some degree, stories of progress and improvement. But this progress comes at a cost; the success of some is bought at the expense of others’ failures. We could end the year on a pessimistic note, with Edward Gibbon –  “History is little more than the register of the crimes, follies, and misfortunes of mankind” or Charles Darwin – “What a book a devil’s chaplain might write on the clumsy, wasteful, blundering low and horridly cruel works of nature!” Instead, for a final thought, I’ll finish by quoting myself from two years back, on New Year’s Eve 2015:

Darwin’s theory implies that some organisms are adapted, as a result of cumulative natural selection, to survive and reproduce, often at the expense of others. We’ve seen on Logarithmic History how much of evolution has been driven by evolutionary “arms races,” especially between predators and prey. And we’ve seen that group-against-group competition is arguably a major motor of human social evolution. It’s possible to draw a grim lesson from this: that we must embrace violent struggle and population replacement as our destiny. But there are more palatable options.

So here’s a different take: At the beginning of The Godfather, movie and book, Michael Corleone, the scion of a mafia family, is set on getting out of the bloody family business, and going straight. In the story, he fails, and is drawn back into a life of violence. The tragic arc makes for a great story, but there’s nothing inevitable about it. By analogy, every one of us is the product of a long evolutionary and cultural history which includes generous helpings of violence. But history is not destiny: there’s no reason we can’t get out of the old bloody business of our species, and go straight.

* although his Chinese < Italian ranking maybe reflects more the prejudices of his time.

Uneven development

1930-1936

If much of the history of Eurasia between 1000 BCE and 1600 CE was shaped by the clash between farmers and city folk, and pastoral nomads from the steppes and deserts, then much of the history of the twentieth century was defined by the collision between Western and non-Western societies. This is one way to see the rise of communism. Traditional Russia and China had developed autocratic institutions that allowed them to cope, more or less, with military threats from the steppe. But these institutions proved desperately unequal to coping with a new set of military challenges from the West and Japan.

Steven Pinker’s book The Better Angels of Our Natures portrays the march of history as a process of diffusion of enlightenment ideals. On a long enough time scale he may be right. But on a medium time scale we see something different – the formation of powerful states on either side of the meta-ethnic frontier dividing industrialized societies from independent but militarily vulnerable peasant societies. Chance and individual personalities played a role in the bloodshed of the twentieth century, but there were also larger forces at work in The World Revolution of Westernization.

Here is a short piece of mine (not from the blog) on History and Group Consciousness relating this topic to arguments about group selection. I argue that taking group selection seriously as an engine of historical dynamics may give us a better understanding of recent history.

Marxism is not very successful as a scientific theory, but in its heyday it was enormously successful as an ideology involved in subordinating masses of individuals in larger collective projects. Here’s a famous speech by Stalin to industrial managers in 1931, in the midst of the first Five Year Plan and the collectivization of agriculture, and on the eve of mass starvation in the Ukraine

It is sometimes asked whether it is not possible to slow down the tempo somewhat, to put a check on the movement. No, comrades, it is not possible! The tempo must not be reduced! On the contrary, we must increase it as much as is within our powers and possibilities. This is dictated to us by our obligations to the workers and peasants of the USSR. This is dictated to us by our obligations to the working class of the whole world.

To slacken the tempo would mean falling behind. And those who fall behind get beaten. But we do not want to be beaten. No, we refuse to be beaten! One feature of the history of old Russia was the continual defeats she suffered because of her backwardness. She was beaten by the Mongol khans. She was beaten by the Turkish beys. She was beaten by the Swedish feudal lords. She was beaten by Polish and Lithuanian gentry. She was beaten by the British and the French capitalists. She was beaten by the Japanese barons. All beat her – because of her backwardness, because of her military backwardness, cultural backwardness, political backwardness, industrial backwardness, agricultural backwardness. They beat her because to do so was profitable and could be done with impunity. You remember the words of the pre-revolutionary poet : ‘You are poor and abundant, mighty and impotent, Mother Russia.’ Those gentlemen were quite familiar with the verses of the old poet. They beat her, saying : ‘You are abundant’, so one can enrich oneself at your expense. They beat her, saying : ‘ You are poor and impotent,’ so you can be beaten and plundered with impunity. Such is the law of the exploiters – to beat the backward and the weak. It is the jungle law of capitalism. You are backward, you are weak – therefore you are wrong; hence you can be beaten and enslaved. You are mighty – therefore you are right; hence we must be wary of you.

That is why we must no longer lag behind.

In the past we had no fatherland, nor could we have had one. But now that we have overthrown capitalism and power is in our hands, in the hands of the people, we have a fatherland, and we will uphold its independence. Do you want our socialist fatherland to be beaten and to lose its independence ? If you do not want this, you must put an end to its backwardness in the shortest possible time and develop a genuine Bolshevik temperament in building up its socialist economy. There is no other way…

We are fifty or a hundred years behind the advanced countries. We must make good this distance in ten years. Either we do it, or they crush us.

 Stalin’s policies were not just a response to perceived external threats, but helped to generate those threats: if the German Communist Party (which took direction from Moscow) had cooperated with the Social Democrats and other supporters of the Weimar government, they could have kept Hitler out of power.

Gradualism

1830-1840

Charles Lyell’s great work, Principles of Geology, came out between 1831 and 1833. Lyell advocated an uncompromising uniformitarianism: the same geological forces at work today, causing small changes over the course of lifetimes, were at work in the past, causing massive changes over the course of geological ages. We’ve seen over the course of this blog that uniformitarianism is not a completely reliable guide either to geology or to human history, which have been punctuated often enough by catastrophes – asteroid strikescontinent-scale floodsvolcanic eruptions, and devastating wars and plagues. But the theory is nonetheless at least part of the story of history, and Lyell’s work was deservedly influential.

In 1837 Charles Darwin, a careful reader of Lyell, published a short article entitled On the Formation of Mould. This would eventually led to his last book, The Formation of Vegetable Mould through the Action of Worms. Darwin’s work on soil formation was Lyellianism in miniature. He demonstrated, through a combination of careful reasoning and experiment, that the surface layer of pasture soil is formed by earthworms. “Although the conclusion may appear at first startling, it will be difficult to deny the probability that every particle of earth forming the bed from which the turf in old pasturelands springs, has passed through the intestines of worms.” Reading Darwin on worms you get the feeling he identifies with his humble subjects, gradually remaking the world through their patient industry.

The doctrine of progress through gradual change was appealing not just for scientific reasons. In the 1830s, English liberals (of whom Darwin was one) were attempting to reform their society gradually, without the violence of the French Revolution, and without turning over politics to a Great Man in the style of Napoleon. (Darwin was also a gradualist with regard to his own work: he came up with the theory of natural selection in 1838, but England at the time wasn’t ready for anything so radical, and he didn’t publish On The Origin of Species for another twenty years.)

George Eliot (Mary Ann Evans), a friend of Darwin’s, set her greatest novel, Middlemarch, around the time of the Reform Act of 1832, which moved England one big step closer to a genuinely representative government. The novel’s heroine, Dorothea Brooke, might in another age have been a famous saint, another Theresa of Avila. In the England of her time she has another fate. Here is the famous conclusion of the novel, a paean to gradualism and the cumulative force of small deeds:

Her full nature … spent itself in channels which had no great name on the earth. But the effect of her being on those around her was incalculably diffusive: for the growing good of the world is partly dependent on unhistoric acts; and that things are not so ill with you and me as they might have been is half owing to the number who lived faithfully a hidden life, and rest in unvisited tombs.

We are MacApes, O’Monkeys, and Ben-Reptiles

1764-1777

A couple years back, Jonathan Marx and Jerry Coyne had an online spat on the question “Are humans apes?” (Marx says noCoyne says yes; see also John Hawks, who says no.) I offer my own solution below, after talking about Linnaeus (1707-1778) and biological categorization.

There’s a branch of cultural anthropology that studies “folk biology,” also known as “ethnobiology,” which is (among other things) about how different groups classify living things. Folk biological categories don’t vary randomly across cultures; there are some general principles at work. A quick summary: the basic level of categorization is roughly the genus. American folk genera include oakcrow, and fox (although a lot of Americans today are really bad at folk biology, maybe using that part of the brain for Pokemon.) Many peoples, and most hunter-gatherers, only take categorization down to the genus level. Others (especially horticulturalists) take it down to the species level, often with two part names (red oak, silver fox). Going toward more inclusive groups, genera are lumped together in larger, intermediate-sized, non-overlapping categories (palmhawk), which belong in turn to the more inclusive level of “life forms”: (bird, snake, fish, tree, grass/herb).

From an anthropological perspective, Linnaeus’s famous scheme of classification is an elaboration of these universal principles, with more species and more taxonomic levels (the famous Kingdom, Phylum, Class, Order, Family, Genus, Species).

A version of Linnaeus’s scheme served evolutionary biologist well for centuries. But starting in the later twentieth century, many biologists turned to another approach that was claimed to be a better fit for evolutionary principles: According to cladists, the classification of living things should be based on clades: groups containing all and only the descendants of an ancestor. This requires overturning or revising many familiar categories. For example, monkeys are not a clade, since Old World monkeys are more closely related to apes (including humans) than to New World monkeys. Reptiles are not a clade, since crocodiles are more closely related to birds than to lizards and snakes. Fish are not a clade, since lungfish are more closely related to amphibians and reptiles than to most other fish.

After some bitter disputes. cladists seems to have won the battle among scientists. But cladism has made less headway among non-scientists. In Naming Nature: The Clash Between Instinct and Science, Carol Yoon argues that cladistics is just too much at variance with the way the human mind understands biological categories. Most people are never going to take to cladistics any more than they’re going to take to twelve-tone music, or Loglan. So different answers to the question “Are humans apes?” reflect disagreement about how far we can or should bring folk categories in line with the austere logic of cladism. Apes, including humans, are a clade. Apes, not including humans, are not (since chimpanzees are more closely related – but not really more similar – to humans than to gorillas).

I suggest a compromise. Folk categories like ape, monkey, reptile, and fish, defined by shared ancestral traits, are useful, even if they aren’t clades, defined by shared derived traits. But the concept of a clade is also important one for biologists. So maybe when we want to talk about the clades associated with folk categories, why don’t we use a prefix – the Scottish Mac, Irish O’, or Hebrew/Arabic ben/bin. (Any of these will serve.) So human beings are not apes, monkeys, reptiles, or fish. But we are MacApes, O’Monkeys, Ben Reptiles, and/or Bin Fish.

(For other We Are posts see We Are Upside Down Bugs and We are Stardust.)