Between Darwin’s and Saint Valentine’s Day

1.23 – 1.18 billion years ago

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. (Here’s one drawback, according to The Onion.)

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. One 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. The general answer is probably that an asexually reproducing organism almost never produces any offspring who have fewer harmful mutations than she has. But a sexually reproducing organism, passing on a random half of her genes to each of her offspring, can have some offspring with fewer harmful mutations, at the cost of having other offspring with more. There are various reasons (Muller’s ratchet, Kondrashov’s hatchet) why this could be evolutionarily advantageous.

In other words, with sexually reproduction, at least some of mum and dad’s kids can be less messed up than their parents; it’s asexually reproducing organisms that really embody Larkin’s dour verse … 

Man hands on misery to man,

It deepens like a coastal shelf

Get out as early as you can,

And don’t have any kids yourself.

Philip Larkin. This Be the Verse

… insofar as, when eukaryote species give up sex, 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

Central Dogma blues

3.40 – 3.23 billion years ago

[T]he Darwinian process may be described as a chapter of accidents. As such, it seems simple, because you do not at first realize all that it involves. But when its whole significance dawns on you, your heart sinks into a heap of sand within you. There is a hideous fatalism about it, a ghastly and damnable reduction of beauty and intelligence, of strength and purpose, of honor and aspiration, to such casually picturesque changes as an avalanche may make in a mountain landscape, or a railway accident in a human figure. If it be … a truth of science, then the stars of heaven, the showers and dew, the winter and summer, the fire and heat, the mountains and hills, may no longer be called to exalt the Lord with us by praise; their work is to modify all things by blindly starving and murdering everything that is not lucky enough to survive in the universal struggle for hogwash.

.George Bernard Shaw. Back to Methusaleh. Preface iv

A broken symmetry lies at the heart of life, ruling out Bernard Shaw’s preferred mechanism of change, Lamarckian evolution through the inheritance of acquired traits. “Lamarck … held as his fundamental proposition that living organisms changed because they wanted to. As he stated it, the great factor in Evolution is use and disuse.” (Back to Methusaleh, preface ii)

Shaw was not attacking Darwin himself. He knew that Darwin accepted the inheritance of acquired traits as one mechanism of evolution. In fact Darwin put a lot of ingenuity into trying figuring out how the process might work. But this was all wasted effort on Darwin’s part. In Shaw’s day, August Weismann had countered Lamarck, arguing that the inheritance of acquired traits was ruled out by one great asymmetry: the separation of germ plasm (destined to pass on to the next generation) from soma (destined to perish).

With the discovery of the DNA double helix, biologists came to recognize an even more profound, more ancient asymmetry. This asymmetry is codified as the Central Dogma of molecular biology: information passes from nucleic acids (the basis of genetic inheritance) to proteins, but not vice versa. 

The Central Dogma may be a predictable, inescapable result of selection acting at multiple levels, both within and among protocells, at the very origin of life, assigning some molecules the necessary but dead-end job of catalysis, giving others a shot at immortality as replicators. 

We developed a model consisting of a population of protocells, each containing a population of replicating catalytic molecules. The molecules are assumed to face a trade-off between serving as catalysts and serving as templates. This trade-off causes conflicting multilevel selection: serving as catalysts is favoured by selection between protocells, whereas serving as templates is favoured by selection between molecules within protocells. This conflict induces informatic and catalytic symmetry breaking, whereby the molecules differentiate into genomes and enzymes, establishing the central dogma. 

The origin of the central dogma through conflicting multilevel selection

Earlier on Logarithmic History, I noted that broken symmetries – female and male, predator and prey, ruler and ruled – are often morally fraught. This applies to the great asymmetry at the center of natural selection. Darwin put a positive spin on it: “From the war of nature, from famine and death, most exalted object which we are capable of conceiving, namely the production of the higher animals, directly follows,” but a many people have found it hard to accept this view of life. In Shaw’s day it was perhaps still possible to hold out hope that Lamarckian evolution provided a gentler path for progressive evolution. And for much of the twentieth century, social scientists tried to quarantine natural selection, allowing it a role in human physical evolution, while sticking to a blank slate view of mind and culture. But there is one more twist in the story: in the twenty first century, the rules of the game may change entirely, as new reproductive technologies present the promise, and peril, of finally overturning the Central Dogma. 

Gradualism

1824 – 1836

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 strikes, continent-scale floods, volcanic 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 for more than just 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.

Nice hair

You’ve probably heard the news – by now it’s pretty old news – that there is more genetic variation within human populations than between them. More specifically, we can say that, averaging across the whole genome, a typical human being will look like they get about 85% of their ancestry from a gene pool they share with all humanity, about 10% from a gene pool specific to a continent-scale race (East Asian, Sub-Saharan African, or whatever), and about another 5% from a localized gene pool (Japanese, Yoruba, or whatever).

This is an interesting statistic. It mostly reflects the fact that different human populations haven’t been diverging for very long (in evolutionary terms). Plus there have been episodes of gene exchange after the initial Out of Africa divergence.

But the statistic is also misleading. It holds for the genome as a whole, where it looks like most genes have not been under strong selection. But the subset of genes that has been under strong selection can differ a lot more between populations. (Slightly off-topic: this is why you can’t plug the numbers for ethnic genetic similarity into the formula for kin selection, and make predictions about ethnic nepotism. See here for a blog post, and here for an article.)

A case in point is the EDAR gene, which encodes a protein active in ectodermal tissues like skin. Somewhere in East Asia around 30,000 years ago, a point mutation occurred in this gene, a single nucleotide substitution. The mutant allele spread rapidly, and is now found in most of East Asians and New World Indians. The population that entered the Americas must have been at or near fixation for the new version of the gene. This rate of spread is far too great to be accounted for by genetic drift. The mutant must have have had some selective advantage.

Frequency of old (blue) and new (red) EDAR alleles

Charles Darwin thought that the main selective force driving the divergence of human populations was sexual selection. Different groups developed different standards of beauty, and selected mates accordingly. (Here’s an article arguing that culturally transmitted aesthetic standards can drive particularly rapid divergence.) In support of this, we observe that some of the greatest differences across populations, with zero overlap between some pairs of populations, are in readily visible, esthetically charged traits like skin color and hair form.

The EDAR gene acts on physical appearance: it affects hair growth. Carriers of the mutant version have thicker hair shafts, and their hair grows out straight, not wavy or curly. So perhaps sexual selection for thick tresses contributed to the spread of the gene. But before we get carried away with that theory, we should note that the mutant version has several other effects. It causes incisors to develop with a characteristic “shoveled” shape. It results in more numerous sweat glands. It also affects mammary glands, leading to less mammary tissue, but a denser network of ducts to carry milk. A recent article argues that it was differences in survival among nursing infants, rather than mate choice among adults, that gave the First Americans their distinctive hair.

And here’s what a mouse looks like with the EDAR gene.

It’s a small world after all

475 – 450 thousand years ago

The story of human origins is partly a story of Big Things like The Taming of Fire and  The Dawn of Speech. But it’s also the story of some odd byways and quiddities. A nice introduction to some of these is Chip Walter’s book Thumbs, Toes, and Tears: And Other Traits That Make Us Human. (His more recent Last Ape Standing is good too.) Walters considers funny bits of anatomy like our unique big toes and thumbs, and funny bits of behavior like our habits of laughing, weeping, and kissing. Toes and thumbs fossilize, but behaviors can be hard to date, evolutionarily. Presumably these behaviors appeared sometime before modern humans evolved and spread, so let’s pick today’s date. It’s also hard to figure out the exact evolutionary rationale for some of these behaviors. Humor, for example, is not a simple phenomenon: intellectually appreciating a joke, actually finding it funny and enjoying it, and finally laughing, each involve separate areas of the brain.

Laughter, specifically, is a minor human oddity that sheds an interesting light on some big events in human evolution. Robert Provine, a leading laughter researcher, spells out the argument in “Curious Behavior: Yawning, Laughing, Hiccuping, and Beyond.” Chimpanzees have a kind of laugh, a modified vocalized panting synchronized with inhalation and exhalation. Presumably laughter first resulted when panting-during-play evolved into a play signal. But the short bursts of human laughter go further, having freed themselves from synchrony with the inhalation/exhalation cycle. Laughter, in other words, is just one instance of the more general phenomenon of humans having separate controls for vocalization and for respiration. Interestingly, the most prominent examples of complex vocalization – songbirds and some other birds, whales, bats, and humans – are all found in non-quadrupeds. In quadrupeds, breathing is tightly coupled with locomotion: lungs need to be full to stiffen the thorax when the forelimbs hit the ground. Giving up quadrupedalism seems to have allowed for an “adaptive release” in the evolution of vocal abilities in a number of unrelated lineages. So the study of laughter (and other vocalizations) suggests that two key human adaptations – bipedalism and spoken language – are more closely linked than one might have expected.

Another and overlapping set of human particularities involves facial expressions of the emotions. Darwin got a whole book out of this. He concluded (admittedly based on somewhat anecdotal evidence) that different emotional expressions are largely innate. It’s an interesting illustration of his ability to reason from small facts to large conclusions that he also drew a big conclusion about human evolution from this. In Darwin’s day, there were scientists who believed that different human races had evolved from very different prehuman progenitors: one prehuman species giving rise to Europeans, another to Africans, and so on. But Darwin reasoned that the very close similarity in facial expressions (and he had traveled a lot, and witnessed a lot of expressions in a lot of places) and the very similar emotional makeup of humans around the world was evidence that human populations shared a fairly recent common ancestry. Here as in several other cases, a mixture of close reasoning and sheer luck led Darwin to the correct conclusion about evolution long before there was much solid evidence.

Darwin’s work on emotions was neglected for most of the twentieth century by anthropologists favoring a blank slate view of human behavior, but was eventually largely vindicated by a number of researchers, notably Paul Ekman. There is now good evidence for six basic facially expressed emotions: Fear, Disgust, Joy, Anger, Sadness, and Surprise.

If you’re a movie watcher, this list may seem familiar. These emotions (all except for Surprise) are all depicted as little homunculi living inside the head of an 11 year old girl in the animated feature “Inside Out.” Somebody at Pixar Studios knew their Ekman.

So the sappy song is right: There is just one moon and one golden sun, and a smile means friendship to everyone.

Heather erectus, or Women Gotta Stick Together

(Here’s a link to the song, “Women Gotta Stick Together”, a satirical take on female solidarity from the musical sitcom “Crazy Ex-Girlfriend”)

Because boys are much louder and less private than girls, it took me a while to begin to focus on girls’ behaviors. When I did, I was quite surprised to see that the stereotypes that apply to girls’ behavior around the world, such as “sugar and spice and everything nice,” did not fully describe what I was actually seeing girls do. … Girls spend a lot of time talking about other people in their lives … These discussions, however, are not composed simply of saying “nice” things about their family and friends. Often, they are dissecting the most negative aspects of another’s behavior. … Paradoxically, I … found out that two girls or two women talking do not typically help one another, other than to be reassuring. In fact, two unrelated females often can become fast enemies. Because they have so much in common, they need similar physical resources, and beginning in adolescence they may compete for the same men. This creates an inherent conflict in unrelated human females’ relations with one another. … How this plays out leads to some very confusing relationships.Warriors and Worriers: The Survival of the Sexes. Joyce F. Beneson

As Darwin noted, adaptive evolution involves nsexual selection as well as the struggle for existence. Sexual selection is not simply about A surviving and reproducing, but more specifically about A reproducing at the expense of B. This may involve mate choice: A may succeed at the expense of B because he or she is more attractive to the other sex. Mate choice may have shaped both female and male traits in our species. Sexual selection can also involve contests within one sex over who mates with the opposite sex. There have been epochs in the history of our species when some men have acquired many more mates, and left many more offspring, than others, most likely by wielding violence, typically as part of a gang. 

Female-female sexual competition is less conspicuous, but still very real.It may have left its mark on women’s sexual physiology and behavior. One argument goes like this:

Ovulation is less conspicuous in our species than among many other primates. Unless we know them very well, we generally don’t have much idea who among the young women we run into is ovulating. The evolution of concealed ovulation at some point in the human line has been the subject of a lot of theorizing. Most of the theories invoke male mate choice: maybe men were more likely to stick around and provide for women who didn’t reveal when they were and weren’t ovulating. But recent work suggests that, in addition to male provisioning, female-female sexual rivalry and aggression may have been crucial. In an agent-based simulation in which females could secure mateships and provisioning by aggressing against rivals, “concealers” were able to out-reproduce “revealers” because they avoided aggression from other females. In other words, the concealment of ovulation in our species may reflect a long evolutionary history of estrus-shaming (my phrase, not the authors’).

Central Dogma blues

3.79 – 3.60 billion years ago

[T]he Darwinian process may be described as a chapter of accidents. As such, it seems simple, because you do not at first realize all that it involves. But when its whole significance dawns on you, your heart sinks into a heap of sand within you. There is a hideous fatalism about it, a ghastly and damnable reduction of beauty and intelligence, of strength and purpose, of honor and aspiration, to such casually picturesque changes as an avalanche may make in a mountain landscape, or a railway accident in a human figure. If it be … a truth of science, then the stars of heaven, the showers and dew, the winter and summer, the fire and heat, the mountains and hills, may no longer be called to exalt the Lord with us by praise; their work is to modify all things by blindly starving and murdering everything that is not lucky enough to survive in the universal struggle for hogwash.

George Bernard Shaw. Back to Methusaleh. Preface iv

A broken symmetry lies at the heart of life, ruling out Bernard Shaw’s preferred mechanism of change, Lamarckian evolution through the inheritance of acquired traits. “Lamarck … held as his fundamental proposition that living organisms changed because they wanted to. As he stated it, the great factor in Evolution is use and disuse.” (Back to Methusaleh, preface ii)

In Shaw’s day, August Weismann countered Lamarck, arguing that the inheritance of acquired traits was ruled out by one great asymmetry: the separation of germ plasm (destined to pass on to the next generation) from soma (destined to perish). In modern parlance, this asymmetry is codified as the Central Dogma of molecular biology: information passes from nucleic acids (the basis of genetic inheritance) to proteins, but not vice versa. 

The Central Dogma may be a predictable, inescapable result of selection acting at multiple levels, both within and among protocells, at the very origin of life. 

We developed a model consisting of a population of protocells, each containing a population of replicating catalytic molecules. The molecules are assumed to face a trade-off between serving as catalysts and serving as templates. This trade-off causes conflicting multilevel selection: serving as catalysts is favoured by selection between protocells, whereas serving as templates is favoured by selection between molecules within protocells. This conflict induces informatic and catalytic symmetry breaking, whereby the molecules differentiate into genomes and enzymes, establishing the central dogma. 

The origin of the central dogma through conflicting multilevel selection

Earlier on Logarithmic History, I noted that broken symmetries – female and male, predator and prey, ruler and ruled – are often morally fraught. This applies to the great asymmetry at the center of natural selection. Darwin put a positive spin on it: “From the war of nature, from famine and death, most exalted object which we are capable of conceiving, namely the production of the higher animals, directly follows,” but a many people have found it hard to accept this view of life. In Shaw’s day it was perhaps still possible to hold out hope that Lamarckian evolution provided a gentler path for progressive evolution. And for much of the twentieth century, social scientists tried to quarantine natural selection, allowing it a role in human physical evolution, while sticking to a blank slate view of mind and culture. But there is one more twist in the story: in the twenty first century, the rules of the game may change entirely, as new reproductive technologies present the promise, and peril, of finally overturning the Central Dogma. 

Evolution and broken symmetries

8.81 – 8.34 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 over himself” 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 Gaia-Enceladus galaxy that got cruelly torn apart and cannibalized by the Milky Way. Broken symmetries in social life – males and females, kings and commoners – are another matter …

The modern synthesis and the blank slate

August 1941 – November 1946

We’re now dividing time finely enough to include months as well as years.

For most of the later nineteenth century after the publication of On the Origin of Species. biologists were skeptical of Darwin’s proposed mechanism of evolutionary change – natural selection. It was only in the twentieth century that this began to change. When Mendel’s work on heredity was rediscovered in 1900, it was originally seen by many as antithetical to Darwinism. But with the pioneering theoretical work of Fisher, Haldane, and Wright, and the subsequent empirical work of Mayr, Dobzhansky, Simpson, Huxley, Stebbins, and others, Darwin’s theory of natural selection and Mendel’s theory of heredity were combined in what came to be called “the modern synthesis.” Julian Huxley’s book Evolution: The Modern Synthesis marked the coming of age of the theory.

In an earlier post I noted how Lyell’s and Darwin’s embrace of gradualism in explaining the past (as well as George Eliot’s celebration of Dorothea Brooke’s “unhistoric acts” and “hidden life”) had something to do with the political climate in England in the years after the French Revolution and Napoleon. Evolution: The Modern Synthesis was first published in 1942. It’s no surprise that the modern synthesis too was a product of its time, when Nazi Germany and the Soviet Union offered gruesome antithetical demonstrations of how not to think about evolution, genes, and behavior.

Not coincidentally, at the same time that biologists in England and the United States were advancing the modern synthesis, social scientists – cultural anthropologists, behaviorist psychologists – were coming to embrace a strong blank slate view of human nature. (Carl Degler tells the American side of the story in In Search of Human Nature: The Decline and Revival of Darwinism in American Social Thought.) There grew up something amounting to a peace treaty between evolutionary biology and the social sciences, with the two fields agreeing to respect each others’ spheres of influence. Social scientists would leave biology to the biologists, accepting, for example, that neither a good upbringing nor acquired skills can improve your genes. Biologists in turn would largely steer clear of addressing social behavior. For example, the theory of sexual selection, which Darwin developed, and Fisher elaborated, was mostly dropped from the modern synthesis as it matured. Huxley argued (pretty unconvincingly in retrospect) that the elaborate mating dances and ornaments found in so many species were not a product of sexual selection, but merely helped to get individuals to choose the right species of mate. Westermarck’s pioneering work on the evolutionary psychology of incest avoidance and the incest taboo was largely shelved in favor of the shakier theories of Freud and Lévi-Strauss. Even Darwin’s work on emotional expression, which might have seemed fairly anodyne politically, was largely rejected by anthropologists. And the study of prehistory was affected as well.

It was only beginning in the 1960s and 1970s, with the rise of sociobiology, that evolutionary biologists returned to seriously addressing social behavior. Sociobiology: The New Synthesis (1975), by E. O Wilson, made a nod to Huxley in its subtitle. It also announced the end of an intellectual peace treaty, and the opening of an intellectual war that persists up to the present.

And here is my obituary for E. O. Wilson, who died last year.

Gradualism

1823 – 1835

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 strikes, continent-scale floods, volcanic 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 for more than just 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.