Darwin’s first inkling (1837)

Charles Darwin had been back less than a year from his tour on the HMS Beagle and he had been thinking furiously about the paradoxical diversity and commonality of life when he had a flash of insight. He reached for his “B” notebook and scribbled this sketch showing species branching and sub-branching from each other. This is one of the most famous images in science and a popular tattoo among scientists. It does not, however, look a great deal like a tree; it looks like a leftover grape stalk. Darwin does not use the word “tree” or “branch” in his notebook; instead he refers to “gradation” and “greater distinction.” What is most important about this sketch is often edited out of images and tattoos. The large letters at the very top read, “I think”: simultaneously a recognition of his own uncertainty and an expression of his way of working through problems. Darwin was 28 years old.

The Origin of Species (1859)

By the time Darwin came to publish The Origin of Species, he had been thinking about evolution for a further 22 years. The concept of speciation was more than just a cluster of splitting lines, it was a fully grown Tree Metaphor. The image above is the only diagram in the first edition of Origin. Instead of being a map of branches, Darwin has now added time as an axis to his map so that the early life forms begin at the bottom and move through time towards the top, branching as they go. Each horizontal line represents “a thousand generations; but it would have been better if each had represented ten thousand generations.” The diagram has also expanded its ambition to include extinctions and evolutionary cul-de-sacs. The diagram still does not look much like a tree. River weeds, maybe.

In the text, though, Darwin waxes prolix on the concept of the Tree of Life: “The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth.” What follows is one of his most memorable passages.

From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.

Beautiful ramifications, indeed. Gorgeous writing, and also very precise. From the diagram and from the text Darwin was very careful to neither imply nor refute a universal common ancestor. The Tree of Life referred to “all the beings of the same class” and not to all life on Earth. There might be one Tree or several. Darwin could not know and does not proffer an answer. Darwin wanted the reader to be very, very clear that the Tree of Life is a metaphor. In one sentence he calls it a “representation” and in the next a “simile.”

Ernst Haeckel’s flamboyant Tree of Life (1866)

Darwin wrote Origin of Species for other naturalists. Popularising the theory of evolution fell to others, possibly because Darwin’s gentle disposition did not lend itself to the rough-and-tumble of public debate where more combative personalities such as Thomas Huxley were to shine. Among the great popularisers was Ernst Haeckel, a German biologist who is best remembered today for his artworks. Haeckel’s illustrations are still considered among the most beautiful scientific drawings in history. Wikipedia hosts a small sample of his prolific output. In 1866, Haeckel wrote the first great popular book explaining evolution, and it includes this image of the Tree of Life:

Unlike Darwin’s stremlined diagram, Haeckel created a work of art. In the process, Haeckel lost two important features of Darwin’s Tree. First, Haeckel implied a universal common ancestor. Today we have good reason to hypothesise a universal common ancestor or at least a set of universal common ancestors, but most of the evidence upon which this rests was unimaginable in Haeckel’s time. Haeckel guessed right, but it was still a guess that he should not have dressed up as a certainty. Second, Haeckel abandoned the depiction of extinctions. Where Darwin laid out a number of dead branches on his evolutionary Tree, Haeckel ignores them altogether. What appear to be dead ends are not extinctions at all — those dead ends include molluscs and lichens and amphibia, creatures very much alive today. In fact, the dead ends don’t represent anything at all, they are simply the artist’s way of squeezing a lot of branches inside a rectangular border.

Despite Haeckel’s great contributions to art and science, his legacy is controversial today. He is the creator of a famous illustration of embryological development that his detractors consider fraudulent and even his most admiring apologists consider sloppy. Even harder to swallow, Haeckel came to be one of the foremost exponents of polygenism, a particularly revolting pseudoscientific formulation of racism that was directly at odds with everything Darwin stood for.

Haeckel’s Grand Oak (1879)

Thirteen years later, Haeckel returned to the Tree of Life in a book called The Evolution of Man. The Tree, as you can see, has flourished. It has grown from a bush into a massive oak that could have come from the deepest glades of the great forests of Europe. As art it is more awe-inspiring than Haeckel’s straggly bush of 1866, but as science it is even more flawed. The extinctions are still missing from the picture and the unwarranted assumption of a universal common ancestor persists; compounding his errors Haeckel has implied a heirarchical structure to the tree with humans, sorry (CAPS-ON) “MAN,” at the top. We even get a box around us to remind us how important we are.

According to Haeckel, the mammalian section of the tree grew out of the trunk marked Amphibia while the reptiles branch off to the side. Actually, mammals and reptiles diverged from common ancestors called the mammal-like reptiles. Humans, snakes, ostriches, as well as the long-gone dinosauria: we are all amniota, but amphibians are not. As errors go this is forgiveable given the lack of information available to Haeckel at the time, but the way he has gone about his error shows his bias towards humanity. Amphibia get their own massive-girthed trunk while the reptiles and birds get a scrawny branch, all because Haeckel didn’t intuit the correct sequence of divergences that lead to nature’s crowning glory (Western European human males, in case you hadn’t guessed).

Against the Tree of Life

The problem with Darwin’s metaphorical Tree of Life is that he derived it from the small subset of living creatures that were available to his observations. For animals, plants, fungi, and other macroscopic creatures, the Tree of Life is a very good representation of the sequence of divergences and extinctions that make up their history. But life goes back a long way before animals and plants and fungi. The oldest fossils known in Darwin’s time came from the Cambrian era, so Darwin only had access to the last sixth of life’s history.

When we look at our smaller cousins, the ones we need microscopes to observe, we notice that they do not reproduce as we do. Bacteria freely swap clusters of genes between each other. Scientists call this sexual transmission, but it is nothing like sexual reproduction in the animal and plant kingdoms. Bacteria even swap these gene clusters between individuals of completely different orders. Unlike mammals, who can only spread their genes into the next generation and only by mating with mammals of the same species, bacteria live in a massive orgy of DNA-mixing that makes the 1970s look like a church fundraiser (unless, that is, your local church is a pentecostalist megachurch). Some biologists even question whether we should use the term “species” when describing bacteria.

As a result, the Tree of Life for micro-organisms such as bacteria and archeans is a swirl of interlocking pathways. In the more extreme cases, not only do organisms swap packets of DNA, but one organism colonises another and comes to live permanently in a state of symbiosis with its host. The early microbes that swalled chloroplasts and mitochondria became the true bacteria. Those that became nucleated and swallowed mitochondria became the eukaryotes — that’s us, by the way, along with plants and fungi and protists.

One of the most vocal advocates of this view if life is W. Ford Doolittle. His map of evolution looks more like a mesh than a tree. He calls it the web of life.

 

There is little doubt that Doolittle’s web is a much better representation of single-celled evolution than Haeckel’s oak. It is also very up-to-date. It really does represent the best current knowledge. I think he has overplayed his hand by assuming the deep roots of the web are a “Common Ancestral Community of Primitive Cells.” It’s not that I disagree with Doolittle. I think a community of primitive cells is a vastly more likely progenitor of life than a single species, but we know so little about that phase of life that I think it is presumptious to map it as factual.

Resurrecting the Tree

Given that Darwin’s Tree is an excellent metaphor for large multicellular life forms and Doolittle’s Web is an excellent metaphor for single-celled organisms, how can we choose between the two? Well actually, we don’t have to. There are many types of tree besides imposing oaks. Here are two common trees that can act as metaphors for both the webbiness and the branchiness of life’s history.

The banyan tree, as illustrated in Nature over 200 years ago.

 

The base of a strangler fig (personal photograph). The upper reaches of mature strangler figs branch just like other trees.

Darwin’s Tree of Life is not entirely outmoded; it still has utility provided one adapts it to meet new evidence and one recalls Darwin’s original intent. The Tree of Life is a metaphor.

This article is not so woefully wrongheaded as others have been. On all the basic scientific evidence, on Darwin’s mistakes and areas of ignorance, Safina gives a very good account. In fact, his second paragraph is remarkably similar to the first two paragraphs I wrote here. But Safina still manages to make three crucial errors.

Error 1: Charles Darwin wasn’t that important

That all life is related by common ancestry, and that populations change form over time, are the broad strokes and fine brushwork of evolution. But Darwin was late to the party. His grandfather, and others, believed new species evolved. Farmers and fanciers continually created new plant and animal varieties by selecting who survived to breed, thus handing Charles Darwin an idea. All Darwin perceived was that selection must work in nature, too.

All? All??? Safina is keen to downplay Darwin’s personal impact on science. “Credit Darwin’s towering genius…But there’s a limit to how much credit is reasonable,” he writes. I get where Safina is coming from: he’s objecting to the idolisation of Darwin when the current theory of evolution relies on the work of thousands of great scientists who extended and re-examined and in some cases overthrew Darwin’s first ideas. But giving due credit to the scientists who built modern evolutionary theory should not have to involve downplaying Darwin’s insight any more than recognising the development of calculus should diminish the initial insights of Newton and Leibniz.

The fact is that Darwin’s Origin of Species is a colossal intellectual work, not just a description of a rather mundane observation. When Darwin perceived the concept of natural selection, it was important because it gave a workable mechanism for evolution where all Darwin’s predecessors had only vague ideas that creatures might have changed over time. There is a massive difference between observing an event (the failure of classical physics, for instance) and explaining it with a working model (Einstein). Apart from that Darwin gave reams of evidence for his theory. He spent decades collecting evidence before publishing Origin. And finally, he exposed every aspect of his theory to the most gruelling critical analysis possible at the time. As a measure of the greatness of Origin of Species, the chapter on the development of the eye remains one of the most potent demolitions of design-theory, still widely quoted 150 years on, and only equalled in my opinion by two other books: Richard Dawkins’s The Blind Watchmaker and Jacques Monod’s Chance and Necessity.

Error 2. “Darwinian evolution” as a redundant term 

Using phrases like “Darwinian selection” or “Darwinian evolution” implies there must be another kind of evolution at work, a process that can be described with another adjective. For instance, “Newtonian physics” distinguishes the mechanical physics Newton explored from subatomic quantum physics. So “Darwinian evolution” raises a question: What’s the other evolution?

Um, Mr Safina? The term “Darwinian selection” is perfectly acceptable as he was the first to propose the idea of natural selection. You might as well object to “Newton’s Laws of Motion” or “the Galilean Moons.”

The use of “Darwinian evolution” is a much more vexed issue, especially as Darwin himself believed in other forms of evolution that are not part of the modern synthesis (and ironically, Alfred Russell Wallace disagreed with Darwin on this point, describing himself as “more of a Darwinist than Darwin”). But, you see, “Darwinian evolution” is usually used to distinguish it from “Lamarckian evolution” (the theory that offspring inherit traits acquired by their parents) and sometimes “theistic evolution” (the idea that God or gods or pixies or ancient Jewish zombies fiddled with evolution with a directive purpose).

Error 3: Scientists use “Darwinism” to define modern biology

By propounding “Darwinism,” even scientists and science writers perpetuate an impression that evolution is about one man, one book, one “theory.”…[large ellipsis]…

Science has marched on. But evolution can seem uniquely stuck on its founder. We don’t call astronomy Copernicism, nor gravity Newtonism. “Darwinism” implies an ideology adhering to one man’s dictates, like Marxism. And “isms” (capitalism, Catholicism, racism) are not science. “Darwinism” implies that biological scientists “believe in” Darwin’s “theory.” It’s as if, since 1860, scientists have just ditto-headed Darwin rather than challenging and testing his ideas, or adding vast new knowledge.

The error here is that scientists do not talk about Darwinism. When you hear an evolutionary scientist talk about Darwinian evolution, they are talking specifically about the thoughts laid out in Darwin’s own writing — just as scientists who talk about “Copernicanism” (not “Copernicism”) are talking about the specific philosophy that Copernicus expounded in de Revolutionibus; if one wants to talk about the general theory, one talks about heliocentrism, not Copernicanism. Scientists do use the term “Newtonian physics” as a rough synonym for classical physics, but again that is an historical reference; and when scientists talk about modern physics, they call it, well, physics. And just to belabour the point, when working scientists talk about evolutionary theory, they call it evolutionary theory.

The term “Darwinism” is almost exclusively used by creationists for the specific purpose of making a robust scientific theory look like a cultish belief. So when Safina wants to “kill Darwin” and objects to the term “Darwinism,” he is not standing up for science; he is flapping about like a fish on a creationist hook.

My testable prediction: even though this article is all in favour of evolutionary theory, it will be quoted in southern US states in support of teaching creationism as biology. “Kill Darwin?” Why, it’s manna! Surely, Mr Safina, you must be aware of that?

Ball is reviewing a book by Adrian Desmond and James Moore (but not Desmond Moore!) which makes the startling claim that Darwin was prompted to develop evolutionary theory as an argument against slavery. Ball quite rightly points out that this really is yet another in a long line of moralisms applied to Darwin retrospectively. Ball writes:

To the Victorians, [Darwin] was an atheistic agitator undermining humankind’s privileged moral status. In the early 20th century, he became a prophet of social engineering and the free market. With sociobiology in the 1970s, Darwinism became a behavioural theory, while neo-Darwinist genetics prompted a bleak view of humanity as gene machines driven by the selfish imperatives of our DNA.

I think Ball is right on the money here. Darwin was an abolitionist and an evolutionary theorist, but it does not follow that he was one because he was the other. Slave traders claimed that Africans were a separate species to Europeans and therefore it was moral to treat them as property, just like farm animals. And, as Ball writes, “it is hard to dispute Desmond and Moore’s contention that Darwin aimed to overturn the notion, conveniently adopted by slavers, that blacks and Europeans (and other races) were separate species.”

But this is not an evolutionary argument. The fact that blacks and whites have common ancestry is one of the few points on which both evolutionary theory and Biblical literalism agree (albeit from very different premises). What’s more, in evolutionary theory having common ancestors does not mean you are of the same species. This is the entire point behind the concept of speciation, to which Darwin devoted so much writing. Whether two populations are separate species is certainly a biological question, but it is not an evolutionary one. The working definition of a species is a group of organisms capable of producing fertile offspring. The fact that slavers tried to argue that humans were not one species should be seen not as a sign of any scientific dispute, but in the same light as tobacco companies lying about smoking causing cancer and nicotine being addictive. (It is also worth pointing out that even if blacks were a separate species to whites, that would still not make slavery acceptable; the critical question is not speciation but what moral rights should be incumbent upon sentience.)

Ball seems to think that “the many-species view of humankind was not then as nonsensical as it now appears. Data on the long-term fertility of progeny from cross-race unions was scant and often distorted.” But this can only be believed if you take slave trader propaganda at face value. Fertile offspring of mixed parents have been around since time immemorial. The word “mulatto” was first recorded in 1595. The words quadroon (1707) and terceroon (1760) both refer to the offspring of a mulatto and a white person. The word “caste” comes from the Latin “casta raca”, or “unmixed race” — clearly there’s no need for the adjective “casta” if you don’t believe races can mix. Humans can interbreed freely. The Romans knew it and the 18th century English knew it; I see no reason to suspect that 19th century Englishmen didn’t.

Then we go from poor research to utterly abysmal research leading to a gross distortion of Darwin’s views.

It is often said that Darwin cannot be held accountable for these excesses [of eugenics and so on], but their seeds are obvious in his works, most notably The Descent of Man (1871), in which he finally explained what his evolutionary theory meant for humankind. The book echoes the concerns of Galton and others about overbreeding in “the reckless, degraded and often vicious members of society”, such as the “squalid, unaspiring Irishman” who “multiplies like rabbits”. There is a clear natural order of class, rank and race and only Darwin’s insistence on a moral duty to help the weak partly redeems him.

All this, and not least Darwin’s provocative talk of “favoured races in the struggle for life”, seems now to be a residue not only of the chauvinism of the times but of a reluctance to abandon belief in abstract “fitness peaks” that natural selection seeks to scale. In fact, evolution can have no targets; races and species cannot be “perfected”.

I have no idea where Ball got the idea that when Darwin said “favoured” he or anybody else took it to mean “perfected.” But there’s another problem with this: when Darwin used the phrase “favoured races,” he was not reflecting the chauvinism of his times. He meant it as a synonym for favoured species and he was not talking about human races. How do we know this? The full title of the book is The Origin of Species By Means of Natural Selection, or The Preservation of Favoured Races in the Struggle For Life – the book is all about species and speciation and Darwin very carefully excluded humans from the book. This is a well-documented piece of creationist quote mining. I think it behooves a science journalist to know better.

Worse still is Ball’s unquestioning repetition of the phrases ”the reckless, degraded and often vicious members of society” and “squalid, unaspiring Irishman multiplies like rabbits.” The problem here is that Darwin did not say these things himself. He was quoting other writers, in the first case Galton and in the second case a Mr W.R. Greg. And if Ball had actually openedThe Descent of Man, he would know that Darwin made it quite clear that this is the opinion of others and immediately sets out to show some strong counter-arguments. “There are, however, some checks to this downward tendency,” Darwin writes before launching into a lengthy and sophisticated look at the evidence against the eugenic view.  For instance:

“It has been urged by several writers that as high intellectual powers are advantageous to a nation, the old Greeks, who stood some grades higher in intellect than any race that has ever existed…ought, if the power of natural selection were real, to have risen still higher in the scale, increased in number, and stocked the whole of Europe.

This is Darwin’s riposte to genetic determinism as an explanation for the rise of civilisations. And Darwin is quoting Galton. Thus even Galton was a more sophisticated thinker than modern critics would like to admit (even though he was still wrong on many counts, including the moral argument). And there’s this:

The remarkable success of the English as colonists, compared to other European nations, has been ascribed to their “daring and persistent energy”; a result which is well illustrated by comparing the progress of the Canadians of English and French extraction; but who can say how the English gained their energy?

Again, Darwin goes on to reject evolutionary superiority as an explanation, calling the mechanisms behind the rise of civilisations “obscure.”

The Descent of Man is widely available and is free online courtesy of the Gutenberg Project. It would be nice if writers and reviewers could go to the effort of actually checking the context of the quotes they use. It is time to stamp out Research by Search String in which finding a phrase in a text is considered the same as proving the author’s intention. Darwin’s views on racial and sexual equality were about as enlightened as it was possible to be in his time; that does not make him a truly modern moralist, just better than almost any of his contemporaries (and to be fair his views are a lot more defensible than those of many of today’s opinionistas). It is no disservice to his legacy to be honest about it. But it is a disservice to exaggerate it, especially as this is a misrepresentation particularly dear to the hearts of creationists.

Far from “echoing” Galton’s views, Darwin quoted them in order to show their deficiencies. One wonders why one couldn’t equally ascribe those quotes to the journalists who “echo” them. After all, Mr Ball, you yourself wrote that the Irish are squalid and unaspiring. We have it in writing.

Observe the New Scientist cover above.

This is the final straw for me. I used to subscribe to New Scientist, but after reading a series of very poor articles I let the subscription lapse. Since then, I have bought a few issues from the newsstand and I see the occasional story referred on by email, and I am saddened by its descent from a truly grand science magazine into a venue for anti-scientific tripe. (See also this open letter written by Greg Egan criticising a cover article full of pseudo-physics.) At this point, I have gone beyond being disappointed in New Scientist. Dismayed and mistrustful would be better words now.

So what is wrong with this story? Well, in a nutshell, it is not the topic per se — the article by Graham Lawton explores several views on a concept that is well worth writing about: that is, one of the metaphors Darwin used to explain evolution is deficient as a total theory of biology. There are, however, a number of flaws in the article, not the least of which being that Darwin never intended the Tree of Life to be a total theory of biology and always presented it as a metaphor to aid understanding.

But the New Scientist editorial team has elevated the feature to utter irresponsibility by promoting it to the cover with a graphic that looks like it was designed to win the admiration of ID theorists and creationists. Indeed, in less than the two days since the issue came out, the cover has already been seized upon as a propaganda coup by the Discovery Institute and by anti-evolution Catholics.

There is no crime in being misrepresented by creationists. All the best scientists have been — but let’s be very clear, (i) the cover implies that Darwin was wrong fundamentally, and so is evolution — that’s exactly what readers would expect in stories similarly titled “Freud was wrong!” (and so is his psychoanalytic theory) or “Copernicus was wrong!” (and so is heliocentrism), and (ii) there is no way known that New Scientist ran that cover without knowing that it would give succour to creationists.

Even in the UK, around a third of people are either skeptical or outright hostile towards evolution, and even more appalling, a recent survey showed 29% of UK science teachers think it is a good idea to teach creationism alongside evolution in science classes. While New Scientist may not be aware of these particular poll results, it is certainly aware of the underlying trend because it has reported on it many times before. And so, in this environment, any story by New Scientist that appears to add weight to the anti-evolution argument will be seized upon by active creationist organisations, but even more critically, people who have simply drifted into creationism because of their parents’ beliefs or because they were exposed to anti-evolution propaganda in the more retrogressive faith schools, or simply because they keep reading news reports about overthrowing Darwin — after all, this story has already been picked up from New Scientist and repackaged by the Daily Telegraph and the Guardian. It’s not just the lay public who respond to these stories, it is also journalists under pressure to provide new stories, and if New Scientist runs it on its cover, then the majority of journalists (most of whom have no science training) will assume the story is sound and feel safe in repeating it uncritically.

But worst of all is the fact that the general public does not get many ideas from articles and fine-tuned argumentation. Life is too short to develop deep knowledge about everything. Instead, most people absorb the cultural messages around them. The only message most people will take in is from seeing the front cover of New Scientist as they walk past the newsstand; millions of people will brush past and take on board the message that one of the most respected science magazines has announced that Darwin was wrong. Very few will buy the magazine to read the article, which is the only way they will learn that the story is only about a metaphor that Darwin used and not a critique of the theory of evolution.

There is no defence for New Scientist on this one.

Next: A guide to the errors in the New Scientist article.
Next+1: Why Darwin made mistakes but the Tree of Life wasn’t one of them