If, so far, you’ve been finding Mr Darwin’s book tough going (it’s OK, there’s no shame in admitting it), here’s what you should do: skip all that flannel about variation, and start here. This is where it gets serious.
Chapter 3 of the Origin, as its opening pages explain, faces in two directions. In chapters one and two, we’ve established the fact of variation, and the fluidity of living forms — both in space, as shown by the blurry boundaries between species, and in time, as shown by the effect of artificial selection on domestic species. In the chapter to come, says Darwin, we’ll be seeing how natural selection mimics human farmers. But why does nature select — why does variation become adaptation?
Because, he says, life is hard, and not everyone can cope:
“We behold the face of nature bright with gladness, we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings are destroyed by birds and beasts of prey; we do not always bear in mind, that though food may be now superabundant, it is not so at all seasons of each recurring year.”
But if this chapter is transitional, reading it is less like crossing a bridge than jumping a canyon on a motorbike.
Ecologists in particular will see their scientific life flash before their eyes. As I read, I scribbled the contemporary jargon for the concepts that Darwin raises in the margin. Here’s that list (if you don’t know what they all are, don’t worry; the point is that there are A Lot):
intraspecific competition, population biology, invasive species, r & K selection, diversity gradients, top-down vs bottom-up population control, niches, abiotic vs biotic population control, epidemiology, density dependence, parasitology, predator satiation, minimum viable population size, succession, food webs, pollination ecology, coevolution, interspecific competition, competitive exclusion, convergent evolution.
The intellectual pace is feverish, but the writing is always lucid: these are not half-baked speculations that Darwin is throwing out, they are fully formed insights. Here, for example, is density-dependent mortality — the idea that population growth is curbed because crowding increases the death rate — in a nutshell, with a side of epidemiology:
When a species, owing to highly favourable circumstances, increases inordinately in numbers in a small tract, epidemics — at least, this seems generally to occur with our game animals — often ensue: and here we have a limiting check independent of the struggle for life. But even some of these so-called epidemics appear to be due to parasitic worms, which have from some cause, possibly in part through facility of diffusion amongst the crowded animals, been disproportionably favoured: and here comes in a sort of struggle between the parasite and its prey.
On other occasions, he doesn’t spell an idea out, but you can see a seed from which many careers have sprouted. Here, for example, is the germ of the notion that parasites will (sometimes) evolve to become less virulent: “The missletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for if too many of these parasites grow on the same tree, it will languish and die.”
If I were running an undergraduate ecology course (which, for everyone’s sake, we can be glad that I am not), I would make this chapter the first thing on the reading list. It’s a capsule textbook, and about twenty-eight times more exciting than any of the required reading I encountered as a student. (No offence, Begon, Harper and Townsend.)
According to Janet Browne’s biography of the Origin, it wasn’t the move away from a literal interpretation of Genesis that shocked Darwin’s readers — that was already well underway in diverse branches of science and theology. It was the vision of nature as ruthless and chaotic.
And this vision hasn’t lost its power to shock. That word ‘struggle’ is repeated over and over at the chapter’s beginning, until it becomes like a chant — Fight! Fight! Fight!, as the audience used to say during playground bust-ups at my school (and that was just the teachers). When did ‘struggle’ turn into the substantially more wishy-washy ‘competition’?
Darwin does claim that he uses the term Struggle for Existence “in a large and metaphorical sense, including dependence of one being on another”. That’s an important point, but in my ears such qualification was drowned out by the sound of what Bertie Wooster would call nature r. in t. and c.:
“[H]eavy destruction inevitably falls either on the young or old”;
“I estimated that the winter of 1854-55 destroyed four-fifths of the birds in my own grounds”;
“Battle within battle must ever be recurring”.
Does Charles Darwin believe that nature, on the whole, is kind? No, on the whole, I think we must conclude that he does not.
And if there’s one thing more likely to give your stereotypical prudish Victorian the creeps than all the death, it’s all the sex. Nature’s power to multiply, says Darwin, is not the harvest-festival fertility of a garden or orchard. Every living thing is straining to overrun the world. There is “no prudential restraint from marriage”: reproduction is both the reason that existence is a struggle and one of the most potent weapons in that struggle.
In which case, thank goodness for the 360° carnage wrought on every species by predators, disease, the climate and, most especially, the other members of its own kind. “Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount.”
Phew. Then after all that excitement, we come to this last sentence:
“When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.”
Isn’t that just the biggest copout of all time? It’s as if William Golding finished Lord of the Flies and thought: ‘That’s a bit bleak. I know (writes): “But Piggy wasn’t dead, he had just bruised his elbow, and all the boys went home to their mummies for tea and buns. The End.” There! Much better — don’t want to bring everybody down.’
Sorry Chuck, the damage is done.
Next, Natural Selection. It’s the longest chapter in the book, but you’ve got the weekend to read it.