Thursday, 31 March 2016

Charles Darwin - puzzlemaster

On the Origin of Species - DarwinCharles Darwin would have been great at jigsaws. I have just finished reading On The Origin of Species (a reprint of the first edition), and the picture it has left in my mind is of a jigsaw puzzle not quite finished. Wikipedia tells me that jigsaw puzzles had been available for nearly 100 years before the book was published. I wonder if the analogy had occurred to Darwin too?

When starting a jigsaw puzzle, the most prized pieces, as we all know, are the corner pieces, closely followed by the other edge pieces. Of the edge pieces, the most valued are the ones which contain transitions in structure (where horizon meets the sky, or the edge of a building appears with the mountains in the background). These transitional features add value when found on the ‘middle pieces’ too, but generally, while sorting through the pile, these are put to one side while the edges are arranged to lay out the boundaries and give a sense proportion to the whole enterprise - although small groups of pieces related by sharing a certain striking feature may be built into small isolated pictures to be positioned tentatively within the framework when their correct positions are more clear. 

Each of these elements are apt analogies for many of the subjects touched upon as Darwin unfolds his theory of evolution.

The corner pieces of Darwin's puzzle are: that for any kind of ‘organic being’ in nature -
  1. Its characteristics are heritable;
  2. In each generation there is variation between individuals;
  3. All but a small minority of individuals in most generations usually die (by the agency of drought, famine,  predators, parasites, disease, etc.) without leaving progeny.
  4. One or more of an individual’s variations may prove favourable to its probability of surviving and, more importantly (at least to the puzzle), of reproducing - thereby tending to preserve those favourable variations in subsequent generations.
  5. There has been enough time for this process to have produced, from “life ...having been originally breathed into a few forms or into one”, all the varied forms of life which have ever existed on Earth.
The first four of these corner pieces are self evident facts, and the ideas inferred by them can be summed up with the closing words of the Sixth chapter (“Laws of Variation”):
Whatever the cause may be of each slight difference in the offspring from their parents—and a cause for each must exist—it is the steady accumulation, through natural selection, of such differences, when beneficial to the individual, that gives rise to all the more important modifications of structure, by which the innumerable beings on the face of this earth are enabled to struggle with each other, and the best adapted to survive. (p 170)
Darwin includes a reasonable amount of discussion about what might be the cause of variation, and his close approximation to the modern understanding in his conclusions on this point is testament to his powers of observation and reasoning, particularly as Gregor Mendel's contemporaneous work in inheritance was apparently unknown to him.

On the fifth point, Darwin, who would have been aware of scientific estimates of the age of the Earth ranging from about 100 million years up to several billion years, had this to say:
The mind cannot possibly grasp the full meaning of the term of a hundred million years; it cannot add up and perceive the full effects of many slight variations, accumulated during an almost infinite number of generations. 
Although I am fully convinced of the truth of the views given in this volume under the form of an abstract, I by no means expect to convince experienced naturalists whose minds are stocked with a multitude of facts all viewed, during a long course of years, from a point of view directly opposite to mine. It is so easy to hide our ignorance under such expressions as the “plan of creation,” “unity of design,” &c., and to think that we give an explanation when we only restate a fact. Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory. (p482)
Darwin’s jigsaw puzzle didn’t come in a box with a picture on the front to tell him what to expect to see when he was finished; and unlike a puzzle which comes in a box, he would not have expected to obtain a complete set of pieces which would fit nicely inside a neat rectangle, with the final piece filling the final gap. The task he set for himself was far more difficult. He collected some of the pieces of his puzzle on his 1837 voyage as naturalist on board the HMAS ‘Beagle’, and over the next twenty-two years many more pieces were procured from the works - both historical and of his contemporaries - of breeders of livestock, pigeon fanciers, physiologists, geologists, etc. as well as from fellow naturalists specialising in a variety of fields. 

These various disciplines could be thought of as providing the edges of the puzzle - they are areas of knowledge which stand independently of the theory of evolution and yet provide a supporting framework by which the various arguments Darwin uses to support his theory are verified, and by which they are located within the ‘bigger picture’ of scientific understanding. Breeders of livestock are cited, along with findings from his own experiments in breeding pigeons and various plants, to demonstrate that the core principle of modification by variation and inheritance is plausible. Physiologist’s opinions are used to confirm that superficial affinities which seem to suggest relatedness between species are in fact more than superficial.

Our analogy, now already stretched, needs a little more stretching because in order for the puzzle of the origin of species to be comprehensible, it must accommodate time and distance in addition to the normal two dimensions with which we are familiar. This is so that we can incorporate migration of populations from their places of origin into other territories (and, often, back again at a later time). To this end, naturalists expert in flora and fauna of different parts of the world are cited to confirm that the distribution of related forms indicates a general correlation between distance of geographical separation and degree of ‘divergence of character’; and Geologists are consulted who verify that the fossil record shows that divergence of character is also broadly related to degree of separation in time as indicated by separation in the geological strata.

This extra dimension can be imagined as a puzzle laid out upon a puzzle repeated many times until it forms a column which represents time. The pieces contained in any one level represent all the organic beings alive at a given moment - interlocked with their neighbours by their mutual struggle for survival. Each level is related to those adjacent by each individual’s relationships to its parents below and its offspring above (make the layers thin enough to show each of the living things and their individual variations and family ties; or as thick as your imagination requires to let them represent whole populations giving rise to slightly different forms across the course of time). At the bottom of this column the earliest form (or forms) of life give rise to a trail of offspring which ascends as a tenuous thread through the lower layers branching occasionally to produce, with gradually increasing variety, the parent forms for all the kinds of living things which appear as we look higher in the column. Once we get three quarters of the way up (about a 600 Million years ago) the puzzle looks nearly as complex as it was at the time of Darwin's writing (some of that complexity has been erased since then). That is, there were about as many different kinds of living things, all of which could be organised into related groups - by order, family, genus, species, subspecies, or variety - but we will trace these forms upwards through time until most of them dwindle and die out as the modified forms of their own offspring replace the now obsolete form of their parents. So as we view each layer of this upper section in turn, we see strange but half-recognisable forms arise which are gradually replaced by newer ones in a repeating pattern as the picture becomes incrementally more familiar until we reach the top layer and recognise life as we now see it in David Attenborough documentaries.

Even this picture is not quite complete (“but wait there’s more!”). We need to also imagine a separate and slightly different column-puzzle being produced within the boundaries of each geologically separate area of the Earth’s surface. Not only that, we need to imagine that each of our columns might receive immigrants from other columns from time to time; or even that some of these columns will merge as the physical barriers separating them are bridged by geological changes which allow free migration of species between them; or that columns might be divided as geological barriers appear and they again need to be imagined as separate and becoming slightly different. And occasionally, here and there, conditions arise where beds of fossils are being laid down providing something like an album of snapshots - tantalising clues for geologists - but when the most interesting things are going on, nature nearly always puts the camera down, and only picks it up again when the excitement is over (as Darwin explains: fossil beds are more often created during periods of subsidence where land masses and related populations are shrinking).

One of the key sources of information which Darwin had at his disposal - and which could perhaps be said to be somewhat analogous to the ‘picture on the box’ or, at least, to collections of ‘middle bits sharing certain striking features’ having been built into small isolated pictures - was the work of the many naturalists who had gone before him who saw their work as categorising and cataloguing the works of ‘The Creator’. In fact there is a whole chapter dedicated to “Classification” where he points out its inherent difficulties - citing cases where quite similar forms have been declared separate species (and therefore deemed to have been separately created) while other, possibly more divergent forms were classified as mere varieties of a single species because intermediate forms were known to exist (either currently alive or evident in fossil records) which connected them by fine graduations, thus suggesting a common ancestry.
Naturalists try to arrange the species, genera, and families in each class, on what is called the Natural System. But what is meant by this system? Some authors look at it merely as a scheme for arranging together those living objects which are most alike, and for separating those which are most unlike; or as an artificial means for enunciating, as briefly as possible, general propositions,—that is, by one sentence to give the characters common, for instance, to all mammals, by another those common to all carnivora, by another those common to the dog-genus, and then by adding a single sentence, a full description is given of each kind of dog. The ingenuity and utility of this system are indisputable. But many naturalists think that something more is meant by the Natural System; they believe that it reveals the plan of the Creator; but unless it be specified whether order in time or space, or what else is meant by the plan of the Creator, it seems to me that nothing is thus added to our knowledge. (p415)
...with respect to the comparative value of the various groups of species, such as orders, sub-orders, families, sub-families, and genera, they seem to be, at least at present, almost arbitrary. Several of the best botanists, such as Mr. Bentham and others, have strongly insisted on their arbitrary value. Instances could be given amongst plants and insects, of a group of forms, first ranked by practised naturalists as only a genus, and then raised to the rank of a sub-family or family; and this has been done, not because further research has detected important structural differences, at first overlooked, but because numerous allied species, with slightly different grades of difference, have been subsequently discovered. 
All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation, or the enunciation of general propositions, and the mere putting together and separating objects more or less alike. (p419)
...Nothing can be more hopeless than to attempt to explain this similarity of pattern in members of the same class, by utility or by the doctrine of final causes. The hopelessness of the attempt has been expressly admitted by Owen in his most interesting work on the ‘Nature of Limbs.’ On the ordinary view of the independent creation of each being, we can only say that so it is;—that it has so pleased the Creator to construct each animal and plant. (p 435)
Surprisingly, this extraordinarily complex and impressively complete multi-dimensional jigsaw puzzle which Darwin has constructed has needed little amendment in the intervening century and a half. Many of the other pieces of the puzzle - ‘the middle bits’ - as assembled by Darwin have remained largely in place. When new discoveries (the DNA spiral helix, understanding tectonic plate movement, calculating the age of the earth, etc.) or scientific techniques (genome mapping, or the various overlapping radio-isotope dating techniques) have had anything to add, it has usually been a matter of filling in the details or adjusting the scale - finding some missing pieces, as it were, or shifting a piece here and there which had been placed provisionally in the first place. The net effect of these amendments has, as happens with a jigsaw puzzle, made the picture easier to see; rather than casting doubt on Darwin’s conclusions it has tended to confirm them. Now when someone, who may think they have found a fatal flaw in the theory, tries to place their piece where it doesn’t belong, it is as obvious - to those familiar with the bigger picture - as someone trying to put a piece of sky into a hillside for no other reason than that it looks about the right shape.

Perhaps the most striking aspect of Darwin’s exegesis of the catalogue of facts at his disposal is that, though his theory has great explanatory power (and no better explanation has yet been suggested), he was aware that falsifiability is a key element of any scientific investigation. Or put another way, intellectual integrity demands that any worthwhile argument must be able to address the objections which may be raised by those not yet convinced by it (and, if possible, any they might yet think of). Remarkably, nearly all of the objections raised in recent times by ‘philosophers and fools’ (as Richard Feynman called them) - where they are not actually objecting against a feature of their own misrepresentation of the theory - were pre-empted by Darwin. It is evident from his writing that he was motivated, above all, by discovering what is true; and the only way to be sure you have not deceived yourself is to honestly evaluate any opposing arguments to ensure that they do not disprove your conclusions or provide a better explanation.

Here are some familiar objections which he considers:

- Irreducible complexity:
If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case. (p189)
(Nor has any such case - so far - been convincingly demonstrated in the intervening years.)

- Animals have characteristics which seem designed to benefit humans or other species:
Natural selection cannot possibly produce any modification in any one Species exclusively for the good of another species; though throughout nature one species incessantly takes advantage of, and profits by, the structure of another.
...If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection. (p200)
- Missing links:
So with natural species, if we look to forms very distinct, for instance to the horse and tapir, we have no reason to suppose that links ever existed directly intermediate between them, but between each and an unknown common parent. The common parent will have had in its whole organisation much general resemblance to the tapir and to the horse; but in some points of structure may have differed considerably from both, even perhaps more than they differ from each other. Hence in all such cases, we should be unable to recognise the parent-form of any two or more species, even if we closely compared the structure of the parent with that of its modified descendants, unless at the same time we had a nearly perfect chain of the intermediate links. (p271)
Cuvier ranked the Ruminants and Pachyderms, as the two most distinct orders of mammals; but Owen has discovered so many fossil links, that he has had to alter the whole classification of these two orders; and has placed certain pachyderms in the same sub-order with ruminants: for example, he dissolves by fine gradations the apparently wide difference between the pig and the camel. (p329)
There are many such points of contention which he addresses (and which are yet, in modern times, raised as objections by those whose ideology demands the acceptance of a narrative at odds with the facts), and many fascinating points of scientific trivia among them (did you know that barnacles are more closely related to lobsters than they are to oysters? Or that not all cuckoos lay their eggs in other bird's nests?). Each point having some bearing on the arguments he is presenting, and contributing incrementally to a beautifully complex picture which indicates the kind of history which must have been traversed by life on earth.

On The Origin Of Species is still a very readable book - the English language has not changed much since the time of its writing, though there are some anachronisms which would be deemed not-politically-correct by modern standards - it contains some big words (have Google at the ready) and some long sentences to stretch the attention span. But it remains worth reading because, above all, and apart from being possibly the most important scientific publication ever written, it shows a great mind at work - carefully checking innumerable details and piecing them together to build an edifice of knowledge which is as unassailable as it is beautiful.

There is no better way to end - after saying “if you haven't already; just read it!” - than to quote the words (spoiler alert) with which Darwin himself chose to conclude:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object 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.