It is not usually the case that I write a blog post for a carnival. I usually just write for the blog, then now and then sit down and figure out which posts should go to with carnivals. That is not the case with this post.
Some time ago I thought, while writing a Peer Reviewed Research post, that it would be interesting to write up older papers, classics, or more recent papers that were of great interest for one reason or another but maybe a few years old. Just around that time, this idea of a classic carnival … a carnival of classic science papers … came around (details here and here), and I thought that was a very cool idea.
I have a plan to write a couple of different series of posts, one with Bob Trivers’ papers (see this for a taste), which will come along very easily, as I have taught a course based primarily on his work. Another would be on papers regarding Race and Racism. Again, this would draw heavily on my course on Race and Gender. A third stream of posts may come from the Bioanthropology tutorial I taught at Harvard. That was some years ago, so even the ‘current’ papers from that effort may now be classics (Tim Caro’s work with hyenas springs instantly to mind). Thinking about that approach led me to consider the first paper I usually assigned in that tutorial, and in fact, ‘the’ first paper in the field of evolutionary biology (perhaps, depending on your perspective).
That paper, I thought, is what this post should be about. Darwin and Wallace’s first composite paper on Natural Selection.
The only question remains: How many other people are going to do the same thing? Probably scads of them. So, I’ll have to make this a little different…..
You all know the story, and if not, I provide links a number of excellent recent writeups below. Darwin was part of the established academic elite in Britain at the time that young upstart Wallace came along with an idea very close to what everyone knew Darwin was working on. So key members of those established patched together a talk and a publication so Darwin would not be scooped and Wallace would not be ignored. Exactly who did what and how well it went can be debated, but we do have these two side by side manuscripts to compare two different perspectives.
Here, all I want to do is to present, with minimal analysis, what I see as representative excerpts of each of the two works for you to make an efficient side by side comparison. The full text can be obtained here.
The Malthusian Imperative:
for animals without artificial means, the amount of food for each species must, on an average, be constant, whereas the increase of all organisms tends to be geometrical, and in a vast majority of cases at an enormous ratio. Suppose in a certain spot there are eight pairs of birds, and that only four pairs of them annually (including double hatches) rear only four young, and that these go on rearing their young at the same rate, then at the end of seven years (a short life, excluding violent deaths, for any bird) there will be 2048 birds, instead of the original sixteen. As this increase is quite impossible, we must conclude either that birds do not rear nearly half their young, or that the average life of a bird is, from accident, not nearly seven years. Both checks probably concur. The same kind of calculation applied to all plants and animals affords results more or less striking, but in very few instances more striking than in man
Variation in context and adaptation:
…let the external conditions of a country alter. If in a small degree, the relative proportions of the inhabitants will in most cases simply be slightly changed; …Now, can it be doubted, from the struggle each individual has to obtain subsistence, that any minute variation in structure, habits, or instincts, adapting that individual better to the new conditions, would tell upon its vigour and health? In the struggle it would have a better chance of surviving; and those of its offspring which inherited the variation, be it ever so slight, would also have a better chance.
Besides this natural means of selection, by which those individuals are preserved, whether in their egg, or larval, or mature state, which are best adapted to the place they fill in nature, there is a second agency at work in most unisexual animals, tending to produce the same effect, namely, the struggle of the males for the females.
Diversification and speciation:
Another principle, which may be called the principle of divergence, plays, I believe, an important part in the origin of species. The same spot will support more life if occupied by very diverse forms.
Critique of the stability of ‘species’
…varieties [subspecies or breeds] … are … unstable, and often have a tendency … to return to the normal form of the parent species; …
[this observation]… has led to a very general and somewhat prejudiced belief in the stability of species. Equally general, however, is the belief in what are called “permanent or true varieties,”–races of animals which continually propagate their like, but which differ so slightly (although constantly) from some other race, that the one is considered to be a variety of the other. Which is the variety and which the original species, there is generally no means of determining, except in those rare cases in which the one race has been known to produce an offspring unlike itself and resembling the other. This, however, would seem quite incompatible with the “permanent invariability of species,”…
… it is the object of the present paper to show that … that there is a general principle in nature which will cause many varieties to survive the parent species, and to give rise to successive variations departing further and further from the original type…
The life of wild animals is a struggle for existence. The full exertion of all their faculties and all their energies is required to preserve their own existence and provide for that of their infant offspring. The possibility of procuring food during the least favourable seasons, and of escaping the attacks of their most dangerous enemies, are the primary conditions which determine the existence both of individuals and of entire species. …
Even the least prolific of animals would increase rapidly if unchecked, whereas it is evident that the animal population of the globe must be stationary, or perhaps, through the influence of man, decreasing. Fluctuations there may be; but permanent increase, except in restricted localities, is almost impossible….
And more selection
… so long as a country remains physically unchanged, the numbers of its animal population cannot materially increase. If one species does so, some others requiring the same kind of food must diminish in proportion. The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be the weakest–the very young, the aged, and the diseased,–while those that prolong their existence can only be the most perfect in health and vigour–those who are best able to obtain food regularly, and avoid their numerous enemies. It is, as we commenced by remarking, “a struggle for existence,” in which the weakest and least perfectly organized must always succumb.
Species level selection (or macro patterns of evolution)
Now it is clear that what takes place among the individuals of a species must also occur among the several allied species of a group,–viz. that those which are best adapted to obtain a regular supply of food, and to defend themselves against the attacks of their enemies and the vicissitudes of the seasons, must necessarily obtain and preserve a superiority in population; while those species which from some defect of power or organization are the least capable of counteracting the vicissitudes of food, supply, &c., must diminish in numbers, and, in extreme cases, become altogether extinct. Between these extremes the species will present various degrees of capacity for ensuring the means of preserving life; and it is thus we account for the abundance or rarity of species…
The nature of the arguments are very different, but the principles at work are similar. Wallace and Darwin have different (but overlapping) mechanisms in mind for the source of variation, and both are pretty undeveloped at this stage. Both have strong Malthusian principles at work, both have a range of descriptions for the kinds of competition. Wallace sees more inter-species struggle than Darwin discusses here, but if you read the rest of Darwin, they are not too different in this respect. It has been fashionable to underscore the differences between them (and that is quite interesting) but if each of these writings were proffered as answers to an AP biology exam question asking “What is Natural Selection … how does it work and what is the evidence for it?” the two essays would score about the same grade.
I wonder what the grade would be?
Darwin, C. R. and A. R. Wallace. 1858. On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection. [Read 1 July] Journal of the Proceedings of the Linnean Society of London. Zoology 3: 46-50. On line here.
I’m including this on the Sb peer Reviewed Journal Article Feed because I regard this as a peer reviewed article. If you don’t, let me know. We can talk.