On the Origin of Species

In his Autobiography, DarwinReference Darwin¹ wrote of his book as containing ‘one long argument’ (p. 140). What was the conclusion towards which he was arguing? Obviously evolution, but note that it was evolution of a particular kind, namely branching evolution leading to a tree-of-life history for all organisms, living and extinct, from (as he said) ‘few forms’ or one (Ref. Reference Darwin2, p. 490). He was also arguing for a mechanism of this evolution, namely natural selection brought on by the struggle for existence. In addition, it was the case that Darwin, like (to name one of the best-known evolutionists of our own times) John Maynard Smith,Reference Maynard Smith³ thought that the major defining mark of the living world is its ‘adaptive complexity’ – organs like the hand and the eye seem as if designed for the benefit of their possessors. Natural selection speaks to this.

How did Darwin set about making his case? Methodologically, he was guided by the experts in the field. Most particularly Darwin took note of the prescriptions of the two leading philosophers of science, John F.W. HerschelReference Herschel^4, Reference Herschel⁵ and William Whewell.Reference Whewell^6, Reference Whewell⁷ They both agreed that the best kind of science is Newtonian; that is, the Newton of the mechanics, and that in order to be Newtonian one must exhibit a vera causa. There was some considerable debate over what precisely this all means, although Herschel and Whewell did agree that good science is hypothetico-deductive, that is axiom-like with initial law-like premises referring to causes, and that all else, particularly more phenomenal-type laws, follow (ideally) deductively. Where they did differ was over the evidence for verae causae, with the more empiricist Herschel preferring analogies and direct evidence (what one might call eye-witness testimony) and the more rationalist Whewell preferring inference to the best explanation – all discoveries and sub-branches gathered together in one synthesis, what he called a ‘consilience of inductions’ (what we might call indirect or circumstantial evidence).

In the Origin, Darwin took note of the various prescriptions and tried to satisfy them all! You can think of the overall argument going in three consecutive stages (ignoring bits and pieces like answers to objections). First, there is the analogy with artificial selection. Second, there is the derivation of natural selection from the struggle for existence. Third, there is the showing that selection is a cause that bears a consilience.Reference Ruse^8, Reference Ruse⁹ In a letter written a year or two after the Origin was first published, Darwin made explicit mention of his strategy.

Artificial Selection

First, Darwin argued that animal and plant breeders have achieved huge successes, changing organisms in desired directions, through artificial selection.

It is almost certain that Darwin was led to natural selection through the analogy with artificial selection.Reference Ruse¹¹ In the Origin, however, it is clear that although Darwin is happy to use this analogy for pedagogical purposes, leading the reader gently from the known to the unknown, it is clear that the analogy also has a justificatory role. The implication obviously being that if artificial selection can get these sorts of results in so short a time, then there is every expectation that natural selection will be able to do no less, and indeed probably a great deal more. In short, with the world of breeders, Darwin has exactly the kind of direct observational evidence that the empiricist Herschel was demanding for claims about vera causa satisfaction? Through the analogy Darwin tried to show that it is reasonable to think of natural selection as a genuine Newtonian cause.

The Central Core

The second section of the argument of the Origin introduced natural selection. Darwin made the case that there is lots of variation in nature, and then he was ready to bring in the struggle for existence.

After this, natural selection.

Then came subsidiary issues, like sexual selection and the so-called principle of divergence – organisms do better by trying different ecological niches (with appropriate adaptations) rather than simply competing head on. This led to the tree of life.

I am sure that in this part of the Origin he was offering us as close an example of a hypothetico-deductive system as he was ever able to achieve.Reference Ruse¹² First, Darwin offered law-like claims about the tendency of organisms to increase in number at a geometrical rate, and the inevitable limitations of food and space. This leads to the struggle. Then, with the struggle and the inevitable variation in natural populations, this leads to natural selection. Note the use of words like ‘inevitable’ and ‘must,’ and the challenge ‘can we doubt.’ With backing like this, the vera causa status of natural selection is established.

The Consilience

The third part of the Origin is where, thanks to natural selection, we have the gathering of all of the various sub-disciplines of biology beneath the over-arching hypothesis of descent with modification. In turn, we go through behavior or instinct, hybridism and the links and gaps between groups, paleontology and the fossil record, biogeography and the distribution of organisms, systematics, anatomy, embryology, and ending with a gasp at rudimentary organs. So, for instance, in the case of instinct we get the explanation through selection of a beautiful example of what Richard DawkinsReference Dawkins¹³ has called the ‘extended phenotype.’ Why is it that honey bees build hexagonal spaces for their young? Why not squares or circles or whatever? Through a number of rather ingenious experiments (involving the use of colored wax to see exactly how and when the bees use their building materials) Darwin was able to show that this is the most efficient use of the wax and as strong as you are ever going to get.

Moving on to the fossil record, much of the time Darwin was on the defensive, trying to show why it is that there are so many gaps in the record. But then he started to make the positive points, particularly about the extent to which one finds earlier fossils in the record, fossils that look like the combination of very different extant organisms. Lying behind a discussion such as this was the kind of Germanic thinking that led the anatomist Richard OwenReference Owen^14, Reference Owen¹⁵ to his archetypal theory, where organisms within a group (like vertebrates) are seen as modifications of a basic groundplan or archetype – what Stephen Jay Gould was to call a Bauplan.Reference Gould and Lewontin¹⁶ For an idealist like Owen, there was considerable doubt as to whether the archetype was a real organism, but for Darwin it was always an ancestor. It was this fact that led him to argue that his theory could take the Germanic thinking under its wing and show it to be derivative and not basic.

Biogeography was always going to be a winner for Darwin, since it was the denizens of the Galapagos that set him on the road to evolutionism. Of course, there had to be a lot of discussion about how organisms could cross large oceans – Darwin always favored rafts and like phenomena rather than now-vanished land bridges – but basically it was gravy all of the way, as Darwin showed how the oddities of geographical distribution fall away under the gaze of natural selection. The Galapagos naturally had a starring role, as did the fact that the organisms of islands tend to resemble their neighbors on local land masses rather than animals and plants on lands far away.

Darwin moved on through the fields. Systematics makes sense because of common descent. Anatomy comes to life because of evolution through selection. Phenomena noted and mysterious since the time of Aristotle – the homologies (as Richard Owen labeled them) between animals of very different lifestyle – are truly inexplicable if one is thinking purely in terms of function. ‘What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?’ (Ref. Reference Darwin2, p. 434) But of course they make perfectly good sense within the Darwinian picture. ‘The explanation is manifest on the theory of the natural selection of successive slight modifications,—each modification being profitable in some way to the modified form, but often affecting by correlation of growth other parts of the organisation. In changes of this nature, there will be little or no tendency to modify the original pattern, or to transpose parts’ (Ref. Reference Darwin2, p. 435).

Embryology, as we draw to a close, was a particular point of triumph for Darwin. Everyone knew that the embryos of very different organisms – human and chick – frequently look very similar. How can this be? Descent with modification, obviously. But then Darwin went into detail, showing how selection and his analogy from the world of breeding can provide real insight. The Darwinian argument is that adults have been torn apart by selection in the struggle for existence. But the young, by and large, are protected from the struggle, so there is no reason to expect them to be made different by selection. Turning to the domestic world, Darwin hypothesized that since breeders are generally interested only in the adults, we should find the young are far less different than their grown parents. Checking on horses – carthorses versus race horses – and dogs – greyhounds versus bulldogs – Darwin found his prediction to be correct, even though breeders had assured him that there was nothing to his supposition.

And so we come to the end of the Origin, with that final flowery passage about entangled banks, singing birds, flitting insects, and crawling worms. ‘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’ (Ref. Reference Darwin2, p. 490).

From Then to Now

Move the clock forward, quickly. Mendelism genetics was discovered, or rediscovered, around 1900.Reference Provine¹⁷ Although at first people saw Darwinian selection and Mendelian heredity as rivals, very quickly it was realized that they are different sides of the same coin. But it was not until around 1930, thanks to the great population geneticists – Ronald FisherReference Fisher¹⁸ and J.B.S. HaldaneReference Haldane¹⁹ in Britain, and Sewall WrightReference Wright^20, Reference Wright²¹ in America – that a full mathematical treatment was developed and presented. Then rapidly after that the empiricists put flesh on the skeleton and modern evolutionary biology was underway. In Britain, it was generally known as neo-Darwinism, and Fisher together with E.B. Ford,Reference Ford²² founder of the so-called school of ‘ecological genetics,’ were the big figures (with Julian Huxley,Reference Huxley²³ Thomas Henry’s grandson, doing the cheering). In the USA, it was generally known as the synthetic theory of evolution, with geneticist Theodosius Dobzhansky,Reference Dobzhansky²⁴ systematist and ornithologist Ernst Mayr,Reference Mayr²⁵ paleontologist George Gaylord Simpson,Reference Simpson²⁶ and botanist G. Ledyard StebbinsReference Stebbins²⁷ being the key figures.

Much happened between the 1930s and the present, the end of the first decade of the new millennium, most notably the coming of molecular biology, but the pattern was set and overall it was really a time of development rather than revolution. Note well, however, that steady development can lead to radical changes. So now I turn to the second major task in this essay, to survey the state of evolutionary studies as they stand today. To survey them, that is, with an eye to what Darwin did and what has happened since to consolidate or revise.

Selection Studies

Start with artificial selection. The evidence of the last 150 years is massive and growing. Moreover, it is seen to be relevant to the overall evolutionary picture, as was argued by Darwin. One of the most famous examples of such selection is a hundred-year plus (it was started in 1896) selection experiment in Illinois on oil content in corn (maize).Reference Dudley²⁸ Starting at around 4 to 6%, we are now up to 16%. In the reverse line, oil content is almost zero. What about the creation of new species? Here also we have positive evidence. One experiment started with a population of corn, mixed between yellow and white varieties, with no reproductive barriers between members of the group.Reference Pasterniani²⁹ Selection was for those plants that favored their own color for reproductive partners, that is white-white and yellow-yellow. Within five generations the two color varieties were much more unwilling or unable to breed with plants that were not of their color. White-yellow and yellow-white liaisons were much reduced. There was nothing particularly mysterious about any of this. White was linked to early flowering and yellow to later flowering. Hence the two varieties were simply not pollinating, that is crossing, together. A species barrier was being erected.

The Core Arguments

Move on now to the second part of the Darwinian argument in the Origin. One thing is that the modern theory is much more formal, much more mathematical, than the theory of Darwin. Today, no one much expects or finds or regrets full-blooded hypothetico-deductive systems. Rather, one gets small systems or models, which are then applied to specific issues of interest.Reference Beatty^30, Reference Beatty³¹ This is certainly the case with modern-day population genetics. Yet, formal or not, there is a major difference between Darwin’s approach and post-Mendel approaches. Rather than trying to prove selection as basic, the ultimate law is the extension of Mendelism to groups, the Hardy–Weinberg Law. This is an equilibrium law – basically it says that, all other things being equal, gene distributions will remain constant – and functions much as Newton’s first law of motion functions, namely as a background, null condition against which change can be introduced and studied. Then the disruptive forces are introduced. These include migration in and out of a population, mutation, and selection. This does not mean that selection is any less important, but that it has a different conceptual position in modern evolutionary biology.

What about direct evidence for natural selection? The most famous example of a study of evolution in action is that of Rosemary and Peter Grant, on the finches of the Galapagos.Reference Grant and Grant^32–Reference Grant³⁵ For over 30 years now, they have been studying – counting and measuring – the birds on a small islet, Daphne Major, looking particularly at beak size and shape. They have shown beyond reasonable doubt that in times of drought the beaks get bigger and stronger, the better to crack and chew up nuts and cactus, and in times of rain the beaks get smaller and finer, the better to handle small seeds and the like. The Grants have counted the living and the dead, and they truly show that these changes are not chance but a function of differential reproduction, that is of natural selection. Darwin quite underestimated the rate of evolution in the wild.

The Tree of Life

Move on now to claims about the tree of life. Start with the roots, namely the question of the origin of life. Darwin simply left the topic undiscussed, making only a casual (actually, a very carefully deliberated) reference to the topic, saying that life came from one or a few forms. He knew full well that across the Channel the final killing thrust was being put into thoughts about spontaneous generation and that even raising the topic could only lead to troubles. So he remained silent, even though – as he admitted in a later letter – he had thoughts about life starting naturally in a ‘warm little pond’ (letter to Joseph Hooker, February 1, 1871, see Ref. Reference Darwin36). Today, the origin-of-life problem is certainly not solved. But we have made incredible advances in that direction.Reference Bada and Lazcana³⁷ We know a huge amount now about the early state of the globe, about when life does seem to have emerged (around 3.75 billion years ago on a planet that started around 4.5 billion years ago), about possible sites (today there is much interest in the possibility that life started down by those hot, chemical rich, deep sea vents), and much more. It is thought, for instance, that the essential early macromolecule might have been ribonucleic acid (RNA) because, unlike its more famous brother deoxyribonucleic acid (DNA), it is capable of self-replicating and of providing its own means of doing so. Obviously, even if this pans out, we are a long way from a functioning cell, but related work moves forward on such issues as the kinds of membranes needed to package the delicate reproducing apparatus within.

What about the tree of life itself. In major respects, this has been a triumph of evolutionary work, especially with the coming of molecular biology and the highly sophisticated ways in which one can tease out relationships. Best known and most exciting is the fact that the tree seems to have three main parts, with simple cells (prokaryotes) now divided into two groups, Eubacteria and Archaea, and then the third branch Eukarya with complex cells (eukaryotes) containing the animals and plants.Reference Woese³⁸ Thanks also to the molecular clock, that is the rates of change as discovered through molecular drift (where one expects uniform change because it is the same random process going on all of the time), we can also start to put some absolute dates on key events in life’s history.Reference Hillis, Huelsenbeck and Cunningham^39, Reference Ayala⁴⁰ This is a major advance on the Origin. Darwin was fully aware of the desirability of quantifying change in some absolute sort of way, and he speculated (in the first edition) on the rate of erosion of the land around his own home (the so-called ‘denudation of the Weald’), but the geologists jumped all over him and so in later editions he removed these speculations.Reference Burchfield⁴¹

Yet is it not a little premature for all of this self-congratulation? One of the big discoveries of recent years is the way in which micro-organisms can incorporate chunks of nucleic acid from their hosts and then move across to other organisms, not at all related to the original hosts, and dump the acquired nucleic acid into the genomes of the new hosts. It has always been known that sometimes organisms hybridize and new forms are created – Darwin has a discussion on this in the Origin – and, thanks to the brilliant theorizing of American biologist Lynn Margulis, it is now generally accepted that complex cells (eukaryotes) were formed by the hybridization of simple cells (prokaryotes).Reference Margulis⁴² But this newly discovered process, involving things like viruses taking genes from one organism and inserting them in another organism is something else again, and supposedly a major and pervasive factor in life’s history.Reference Travis and Ruse⁴³ ‘Horizontal gene transfer’ is a phenomenon sufficiently powerful that, early in 2009, the British popular science magazine The New Scientist carried a cover banner, ‘Darwin got it wrong.’ There is so much swapping of nucleic acid across groups that the true metaphor is a web and not a tree at all.

As Jane Austen would have said, these are not truths universally acknowledged. Richard Dawkins for one has vehemently denied that any of this represents a repudiation of Darwin – as well as pointing out that scary headlines like this are manna from heaven for the Creationists.Reference Dennett, Coyne, Dawkins and Myers⁴⁴ The simple fact of the matter is that the tree, especially among the eukaryotes, has considerable life still in it. No one is saying for instance that the dinosaurs had to incorporate wholesale, let us say, the cabbage genome in order to make the birds. Horizontal gene transfer may well be very, very important, but it is something building on the Darwinian tree rather than refuting it. As Dawkins says, we now have a banyan tree rather than an oak tree.

The Consilience Today

Thirdly, and finally, let us turn to the last part – actually about the last three fifths – of the material covered in the Origin of Species. The consilience. Simply put, this form of argumentation is as crucial today as it ever was. This is not to say that there is no change. There is massive change. It is to say that the structure of the Origin, including here the intention to explain through natural selection, is (notwithstanding the cries of critics) embraced fully by today’s evolutionary biologists. Let us go quickly through the sub-branches or disciplines.

First there is instinct, by which Darwin very much meant social behavior. In the past half century, this whole topic has exploded outwards, in theory and in experiment and in study in nature. It has even been given its own name of ‘sociobiology.’ The key conceptual moves came in the 1960s and early 1970s, when evolutionary biologists – notably William D. HamiltonReference Hamilton⁴⁵ and John Maynard SmithReference Maynard Smith⁴⁶ in Britain and George C. WilliamsReference Williams⁴⁷ and Robert TriversReference Trivers⁴⁸ in America – saw that the right approach is Darwinian: one must explain in terms of benefit to the individual, considering all group effects to be secondary. Really powerful was the already-mentioned process of kin selection, articulated by Hamilton, and of reciprocal altruism, articulated by Trivers. The first saw that help to others, altruism, can be spurred by genetic self-interest and the second saw that such altruism can occur between non-relatives if one has a ‘you scratch my back and I’ll scratch yours’ situation. Rapidly, building on these insights there was massive empirical attention and, by the middle of the 1970s, the world’s leading ant biologist, Edward O. Wilson of Harvard, was able to write his magnificent overview Sociobiology: the New Synthesis Reference Wilson⁴⁹ and Richard Dawkins of Oxford penned his popular account The Selfish Gene.Reference Dawkins⁵⁰

The fossil record always fascinates. Again, in some respects, we are way beyond Darwin. As noted, we have absolute dates now. The beginning of the Cambrian 540 million years ago, for instance. More than this, we have evidence of pre-Cambrian life.Reference Knoll⁵¹ To his embarrassment, Darwin had none and gave textbook examples of scientific adhockery – the fossils would be where the oceans are now and, even if we could drill, the weight above would have squashed them into non-being. Now we have a pretty good record of life from its beginnings and, moreover, this is life which starts simple and gets more complex, precisely as expected. We have lots more transitional fossils, most recently the fish-amphibian Tiktaalik from the upper reaches of snowy Canada. Or if you want a sequence, then the line leading up to humans is excellent.Reference McHenry⁵² Think about Lucy, Australopithecus afarensis, about three and a half million years old, less than four feet tall, on her hind legs although not as good a walker as we (but probably a better climber), with a chimpanzee-sized brain – 400cc as opposed to our 1200cc.Reference Johanson⁵³ (Note that she did not have a chimpanzee brain, but a chimpanzee-sized brain.)

Was Darwin right in seeing (as he did) the history of life as a smooth process, leading from one form to another? For Darwin, this was part and parcel of his commitment to adaptation. Rapid changes would take organisms out of adaptive focus. He had no place for ‘hopeful monsters.’ Famously, the late Stephen Jay Gould together with fellow paleontologist Niles Eldredge argued that the true course of history is much more one of stop and go – periods of relative evolutionary inaction (stasis) broken by times of rapid change.Reference Eldredge and Gould⁵⁴ Much ink has been spilt over this theory of ‘punctuated equilibrium,’ including the question of how smooth a Darwinian gradual change must necessarily be. Ultimately, it is probably true that, as with so many controversies, there is some truth in the Gould–Eldredge hypothesis but nothing like as much as was claimed at times by enthusiasts.Reference Sepkoski and Ruse⁵⁵ Rates of change do vary, but then what would you expect? At the micro-level, change is probably going to be pretty gradual, although precisely what one might mean by ‘pretty gradual’ can be contested. Dimensions might be distorted drastically, very quickly, with major implications. Richard Dawkins’ exampleReference Dawkins⁵⁶ is of a 747 Jumbo Jet being stretched, virtually overnight from the original form, to make for more passengers. We might get a change in (say) reptilian form pretty quickly this way. It is, however, unlikely that we would get something like the overnight change from reptile to bird. And of course the bird–reptile Archaeopteryx shows that this did not happen.

Biogeography was one of Darwin’s strongest supports for his theory and it continues to be so today. But here the changes have been truly staggering, because we are now in the era of plate tectonics, leading to continental drift. Although no one denies the powers of driftwood and the like, there is no need of fabulous hypotheses – and especially not fabulous hypotheses about now-missing land links – because we now know that the continents move around the globe on massive plates, things that arise out of the earth, move in a stately fashion across the surface, and finally return into the bowels in an almost Wagnerian fashion. You can explain, for instance, why it is that the Permian reptile Lystrosaurus, a slug of a brute if ever there was one, can be found in Africa, India, and Antarctica. It did not go traveling under its own volition. It stayed where it was and let the moving plates do the hard work.Reference Ruse⁵⁷

Spandrels and other Worries

Systematics, morphology, embryology – they start to bring the consilience to a close. One could write full-length essays on each of these topics. Change and yet adaptation due to natural selection is the story. Systematics was transformed in the 1970s, thanks to the coming of cladistics, the system of classification based on the somewhat idealistic system of the German biologist Willi Hennig.Reference Hennig⁵⁸ Although there were some (rather extreme devotees of the philosophy of Karl Popper) who questioned whether classifications need reflect history at all, generally it was (and still is) agreed that cladistic classification is firmly evolutionary. It is about paths or phylogenies. Less obvious, particularly at first, was whether it was always very Darwinian. For instance, change in a line without branching would not be (could not be) recorded. As methods have become more sophisticated and refined, however, particularly thanks to the coming of molecular techniques, it does seem that the gap between cladistic practices and results and Darwinian processes has become narrower.

As it happens, like paleontology, morphology has been very controversial, and for much the same or at least related reasons. Stephen Jay Gould argued that form, as in homology, is basic, and function, as in adaptation, comes afterwards. Certainly (according to him and co-writer Harvard geneticist Richard Lewontin) it does in many cases.Reference Gould and Lewontin¹⁶ Most particularly, because form puts its mark on organisms, much that we find has little or no relation to utility. Often, seemingly important adaptations are ‘spandrels,’ that is to say by-products of other characteristics, which may or may not themselves be adaptive. Spandrels are the triangular spaces at the tops of columns in medieval buildings. Frequently, as in the church of San Marco in Venice – with beautiful decorations all over them. ‘The design is so elaborate, harmonious, and purposeful that we are tempted to view it as the starting point of any analysis, as the cause in some sense of the surrounding architecture.’ But this is to reverse cause and effect. ‘The system begins with an architectural constraint: the necessary four spandrels and their tapering triangular form. They provide a space in which the mosaicist worked; they set the quadripartite symmetry of the dome above’ (Ref. Reference Gould and Lewontin16, p. 148). Warming to his theme, arguing that much of the living world is non-adaptive, Gould sneered that those who seek adaptation are too often like Dr Pangloss in Voltaire’s Candide, forever seeing value or use when there is none – ‘the best of all things in the best of all possible worlds.’ According to Gould, Darwinians spin ‘just so’ stories, at one with the fairy tales of Rudyard Kipling, who tells us that the elephant has a long trunk because a crocodile pulled it!

That the organic world is marked by adaptive complexity is, despite Gould’s rhetoric, simply a commonplace. Since Darwin, again and again the most outlandish feature has been shown tightly tied to reproductive utility. Take the triangular plates running along the back of the Stegosaurus, a monstrous dinosaur discovered in the American West in the decades after the Origin. What can they be for? Some have suggested sexual attraction, others have proposed that their utility comes as weapons for fighting or defense. The popular view today is that they are for temperature control, for heating and cooling.Reference Farlow, Thompson and Rosner⁵⁹ The brute needed to warm up its blood first thing in the morning and then, at mid-day, particularly with the heat produced by its herbivorous diet, it needed to get rid of the heat. The plates are just like the fins one finds in electrical cooling towers, where they likewise are used for heat transference. Supporting the hypothesis, the fossil evidence is that the blood was moved from the main body (and back again) in just the efficient way one would suppose were heat transference the goal in mind.

It is no less a commonplace for the Darwinian, starting with the Origin itself, that not every feature is going to be adaptive. Introducing natural selection, Darwin concluded: ‘Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic’ (Ref. Reference Darwin2, p. 81). There are many reasons why features might not be very adaptive or might even be positively non-adaptive. In some respects the peacock’s tail is very adaptive, that is when it comes to attracting the peahen, but is very non-adaptive when it comes to escaping from predators. Walking upright has many adaptive virtues for humans, not the least the way our hands are freed for other tasks. But the cost has been a less-than-well designed lower back, as many sufferers attest. The appendix may have had a role once, but again is not something of much value now, and for some very much something of negative value.

As sociobiology has transformed the study of instinct, so the new field of evolutionary-development has transformed embryology. The molecular biologists have moved in, giving new insights and empirical discoveries, and offering new theories. This is no bad thing, if only in the sense that the neo-Darwinian synthesis of the 1930s followed the population geneticists as regarding development as something of a black box – you have genes (genotypes) on the one side, and you have physical features (phenotypes) on the other side, and no one cared much about what went on in between. Pigs in, sausages out, and no questions please. Now this connection is brought into the sunlight, as biologists trace in detail the paths from the nucleic acids to the performing physical organisms. Some find the experience so giddy-making that they are all for throwing out the old completely.

Well yes. Certainly the first claim is true. Ernst Mayr,Reference Mayr⁶¹ writing in 1963 about homology, having described it as the best of all kinds of evidence for evolution, warned non-biologists not to look for impossible isomorphisms between organisms as different as humans and fruitflies. You are not going to find them. One hopes that wherever he is, looking up or looking down, Mayr now celebrates the fact that at the molecular level there are the most incredible homologies between humans and fruitflies. It turns out that the genes that control development, the Hox genes, are nigh identical between the two organisms – and with many others too.Reference Carroll, Grenier and Weatherbee⁶² But what about the second claim? Why any of this should impact negatively on natural selection is hard to imagine. We now know that organisms are built on the Lego principle – the same building blocks can make the White House or King Kong, a fruitfly or a human. But natural selection has no less of a role. Going back to earlier discussion, it is true that evo-devo shows that often you can get fantastic changes by altering what you have rather than by starting anew – the stretched 747 – but selection is no less important – if the plane does not fly, then it is of no use. From Thomas Henry Huxley on, there has been a downplaying of adaptation, especially by bench biologists who never see organisms alive and well, in their native habitats. But organisms do flourish, in their native habitats, and if biologists forget this fact, if they forget it is one thing to make an organism but then it must succeed in life’s struggles, they will never get the full story of evolution.