Thanks to Logicel for the link.

http://judson.blogs.nytimes.com/2008/07/08/an-original-confession/

An Original Confession

(The second part in a series celebrating Charles Darwin.)

It always happens the same way. A glance around the room to make sure no one else is listening. A clearing of the throat. A lowering of the voice to a conspiratorial tone. Then, the confession.

"I've never read 'On the Origin of Species.' I tried, but I thought it was boring."

Thus, a number of eminent scientists — biologists all — have spoken. Or rather, whispered.

As the first major statement on evolution and how it works, Charles Darwin's "On the Origin of Species" not only transformed the way we humans see ourselves. It marks the beginning of modern biology. But reading it is evidently not a prerequisite for a successful career in biology — not even for those studying evolution.

Which is not surprising. The book was written almost 150 years ago, and the subject has (needless to say) evolved since then. Moreover, the central enduring idea in the "Origin" — evolution by natural selection — can be learned from any number of textbooks.

Nonetheless, those confessions made me wonder. Does the "Origin" have anything fresh to say to a modern reader? Or is it simply of historical interest?

There is no doubt that the book is antiquated in several respects, and Darwin's writing is — in my opinion — patchy. In places, his prose is clear, lyrical and glorious: as good as anything ever written by anyone. One of my favorite passages concerns the fact that some flowers are pollinated only by humble-bees (or bumblebees, as we call them now):

The number of humble-bees in any district depends in a great degree on the number of field-mice, which destroy their combs and nests; and Mr. H. Newman, who has long attended to the habits of humble-bees, believes that "more than two thirds of them are thus destroyed all over England." Now the number of mice is largely dependent, as every one knows, on the number of cats; and Mr. Newman says, "Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice." Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!

But there are also passages that are long-winded, turgid and opaque. Often, these occur when Darwin is writing about subjects that were not understood at the time — such as what we now call genetics.

Beyond the fact that animals and plants tend to resemble their parents more than they resemble members of the population at large, Darwin knew nothing about how traits are inherited, or where genetic variation comes from. For his immediate purposes, this didn't matter much. Natural selection will operate whenever all of three conditions are met. These are: (1) some of the differences between individuals are inherited differences, not due to differences in their environments; (2) more individuals are born than can survive; and (3) part of the reason at least some of the survivors make it is owing to the traits — a longer-than-average beak, say — that they inherited from their parents. For natural selection, then, what is important is that some differences are inherited; and this, Darwin could show. The breeding of animals such as dogs clearly illustrates that some traits are inherited; if they were not, distinct breeds like Belgian shepherds and Pekingese could not exist.

Darwin's ignorance of genetics (of which he was well aware) means that many of the passages where he discusses it are tortuous, in part because he is describing a subject for which the very language did not exist. Darwin himself was the first to use "genetic" in a biological context; terms like "gene" wouldn't be coined for another 50 years, and the structure of DNA — the stuff of which genes are made — wouldn't be worked out for a further 40. He is also puzzled by observations that we can now easily explain. For example, he knew that bald dogs often have bad teeth, but was mystified as to why this should be so. (The reason is that, in the developing embryo, the same set of genes is involved in the initial formation of both teeth and hair. Mutations to those genes thus affect both traits.)

Two other factors make the "Origin" a demanding read today. The first is that Darwin's own knowledge of the diversity of life is immense, and he assumes the reader will be familiar with a wide range of organisms — such as Asclepias (a group of flowering plants commonly known as milkweeds, for their thick milky sap) and corncrakes (stout land-dwelling birds related to waterbirds like moorhens). This means either skating over such words and just absorbing the gist of what he is saying, or spending a lot of time looking things up. Which is fine — but as a result, getting full meaning from the text requires a certain level of prior knowledge, a large dollop of enthusiasm, a good guidebook, or participation in a discussion group.

The other thing that makes the "Origin" tricky is that the text is stuffed with facts and speculations, and it is hard to know which of them are still taken seriously and which are obsolete. He thinks, for example, that all chickens bred by humans are descended from the wild Indian fowl (now known as Gallus gallus gallus). This is right. However, he also says that domestic dogs have been bred from a variety of ancestors in different parts of the world; this is no longer thought to be the case. All dogs are descended from the wolf.

Yet while this is sometimes frustrating, it is also inspiring. He has so many ideas! For instance, he mentions in passing that "it is a general law of nature (utterly ignorant though we be of the meaning of the law) that no organic being self-fertilises itself for an eternity of generations; but that a cross with another individual is occasionally — perhaps at very long intervals — indispensible." This sentence alone has been the subject of countless doctoral theses; and, as far as we can tell, he's basically right. The adoption of asexuality — which is what exclusive self-fertilization amounts to — almost always leads to a rapid extinction. The book, in other words, is a treasure trove of hypotheses and conjectures, many of which still await investigation.

Moreover, parts of the "Origin" still hold great insights. For example, to my mind Darwin's discussion of instinctive behaviors is strikingly modern: he sees that instincts can evolve through natural selection in the same way that physical traits can. (By instincts he means behaviors that do not need to be learned — such as the tendency for a just-hatched cuckoo to heave any other eggs out of the nest it finds itself in.) He has a sophisticated view of how natural selection works, and the circumstances that make it powerful; indeed, his descriptions of the forces of nature — starvation, predation, competition and disease, to name a few — are as good as, or better than, those in most textbooks today. He appreciates that the biggest problems that most living beings face come not from features of the physical environment, such as climate, but from other organisms, whether of the same species or a different one. And in our current age of specialization, where deep knowledge of an animal or a plant often comes at the cost of broad knowledge of other members of the tree of life, it is deeply refreshing to come across writing that is so much about all of nature.

So, the difficulties notwithstanding, there are many reasons to tackle the "Origin." Reasons above and beyond the fact that it is one of the most important books ever written, and central to our culture. But to me, perhaps the most important is that reading the "Origin" is a window into a mind. A rich and fertile mind, with a holistic view of nature. One that sees the interconnectedness of living beings — that cats can alter the number of flowers — long before ecology existed as a formal subject. A mind that sees the brutality of the natural world — the wasps that lay their eggs in the living bodies of caterpillars (the caterpillars are then eaten alive by the growing larvae), the stupendous death rates of most creatures — and sees that from the terrible slaughter, great beauty can arise:

Thus, from the war of nature, from famine and death, the most exalted object of which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

NOTES:

The quotations are taken from the first edition of "On the Origin of Species." The quotation about mice, bees, and cats comes from chapter 3 (page 74 of the Harvard University Press facsimile edition); the quotation about self-fertilization comes from chapter 4 (page 97 of the facsimile); the war of nature quotation is the final paragraph of the book (page 490).

The fact of Darwin being the first to use "genetic" in a biological context comes from "The Oxford English Dictionary," second edition, 1989, volume VI, page 440. The date of introduction of "gene" comes from the same volume, page 428.

For the shared developmental pathways of hair and teeth, see pages 286-287, and the relevant notes, in Leroi, A. M. 2003. "Mutants: On Genetic Variety and the Human Body." Viking.

For the origins of domestic chickens, see Fumihito, A., Miyake, T., Sumi, S.-I., Takada, M., Ohno, S., and N. Kondo. 1994. "One subspecies of the red junglefowl (Gallus gallus gallus) suffices as the matriarchic ancestor of all domestic breeds." Proceedings of the National Academy of Sciences USA 91: 12505-12509. For the origins of domestic dogs, see Wayne, R. K. and E. A. Ostrander. 2007. "Lessons learned from the dog genome." Trends in Genetics 23: 559-567.

Above, I say that "…Darwin knew nothing about how traits are inherited, or where genetic variation comes from. For his immediate purposes, this didn't matter much."

There is an interesting caveat to this. At the time Darwin was writing, inheritance was believed to be a sort of blending of the two parents, almost as though the factors of inheritance were a kind of soup. Darwin knew that blending wasn't adequate to explain all of the patterns of inheritance he observed, but he was at a loss for an alternative. Under blending inheritance, populations should quickly become genetically uniform. When a population is genetically uniform, natural selection can't operate. So for blending inheritance to allow natural selection to work, new genetic variation must be continually introduced at a very high rate. Or, to speak in modern terms, the mutation rate has be exceedingly high. Where variation comes from was thus one of Darwin's major preoccupations. With the system of inheritance that actually exists — namely, genes — variation can be much more readily maintained in the population, and the problem goes away. For further discussion of blending inheritance and its implications for natural selection, and for Darwin's gropings towards a particulate theory of inheritance, see chapter one of Fisher, R. A. 1999. "The Genetical Theory of Natural Selection: A Complete Variorum Edition" (edited by H. Bennett). Oxford University Press.

There are many editions of the "Origin"; I recommend the Harvard University Press facsimile of the first edition. There are also any number of readers' guides and commentaries; as a good starting point, I recommend Ridley, M. 2005. "How to Read Darwin." W.W. Norton.

Many thanks to Dan Haydon, Horace Judson, Gideon Lichfield, Dmitri Petrov and Jonathan Swire for insights, comments and suggestions.