Chapter Three is, in many ways, the beginning of ecology. One of the ecologists in our reading group said that very little in modern community ecology was not laid out there. The concept of organisms interacting with both their environment, other species, and other members of the same species, and indeed the word "competition" in its ecological sense, are if not Darwin's pioneering work alone at least popularised by him (I do not know enough of the history of biology to say which). This chapter was inspired primarily by the work of the economist Thomas Malthus, who analysed the relative birth and death rates in human populations. Darwin's genius was to take this to a mechanical level, without the action of individual intentions. It was one of those ideas which seems obvious in retrospect but which was groundbreaking when first presented. As I read it I kept thinking that this chapter would be an ideal assignment to an introductory ecology class: it really is that comprehensive, that modern. The majority of the work that followed (at least in community ecology) has been merely refinement, primarily through the application of mathematics.
The chapter focuses on what Darwin called the "struggle for existence". The language was meant only partly to be taken literally: while animals must in fact frequently struggle to avoid being eaten, or to subdue rivals, the concept can also be applied to plants (as Darwin did). Those organisms that are able to leave offspring have succeeded in that struggle: they have had to survive long enough to reach reproductive maturity. The struggle goes further for those organisms that must mate in order to reproduce, and still further for those that must nurture their offspring -- but again, the struggle can be metaphorical. Plants which release more pollen, for instance, might win their struggle against others of the same species, in that they would leave more offspring. The struggle to produce viable offspring is implicit in the amount of energy that must be expended to build another organism: pregnant and nursing mothers, for instance, "eat for two", and this intensifies the daily efforts of finding food.
The struggle for existence has its place in the theory of evolution by making explicit the fact that more offspring are produced in each generation than can survive to replace their parents. In a stable population, this means that some offspring will die without having themselves reproduced: they will have lost in Darwin's struggle. Meanwhile, organisms are also individuals, and as such they vary, as was discussed in the previous chapter. Some individuals succeed in the struggle by virtue of inherited characteristics that give them an advantage over their less-endowed kin, and will pass those characteristics on to their own offspring. These advantages may help adapt the organism to its physical environment, or they may help the organism find food or avoid becoming food, or they may help the organism increase its likelihood of reproducing, or the number or health of its offspring.
This leads to the concept of natural selection, which is the topic of the next chapter, but not without offering what must be one of the most obvious attempts at softening the blow in scientific history. Darwin's depiction of Nature is as a brutal and ultimately losing struggle to stay alive, wherein the best that any living thing can hope for is to leave successful offspring before it succumbs to the myriad and overwhelming forces arrayed against it. This must have been appalling to Victorian sensibilities, which Darwin attempts to soothe: "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." I will not deny that there is much joy in life, but fear, sorrow, anger, and pain are also unavoidable. Darwin's empathy for living things is here curiously selective: what of the weak, the sickly, the despondent? Do they really feel no fear? Do they never suffer for long? Of course, the question must here be addressed as to whether other forms of life are capable of feeling fear or suffering pain. It is not my intention to debate that here, except to say that it was this same work of Darwin's that made this question scientifically viable.
But while such a passage fails in any way to support its implication that (in this context) ecological and (ultimately) evolutionary success leads to a more enjoyable life, its greatest failing lies in its assertion that the "struggle for existence" is not constant. Perhaps it is not constant in every aspect of life, but the interactions between living things are so complex that it cannot be assumed that, at one level or another, one is never at loggerheads with something. In finding shelter, we must displace others looking for that same resource. The very act of eating implies that something else had to die: how is that not part of the struggle? Our immune systems are continually fighting off infections -- and doing so the more militantly when we are not aware of it! In winning the hand of one's mate, another must lose the same; what is (one hopes) a happy union for some is necessarily a source of frustration and feelings of loss for others. Nature may not always be red in tooth and claw, but our interactions with one another and with other living things are rarely benign for all.