by Paul Braterman
In my last post, I said that the right way to undermine creationism is to promote appreciation of the science of evolution, by presenting it in ways that are engaging, enjoyable, and above all personal. In this post, I review two more books that succeed in doing this; Alice Roberts' The Incredible Unlikeliness of Being and Jonathan Tweet's Grandmother Fish.
We start with a delightfully drawn Grandmother Fish, who lived a long, long, long, long, long time ago and could wiggle and swim fast and had jaws to chomp with. At once, this is made personally relevant: “Can you wiggle? … Can you chomp?” We proceed by way of Grandmother Reptile, Grandmother Mammal and Grandmother Ape, to Grandmother Human, who lived a long time ago, could walk on two feet and talk and tell stories, and whose many different grandchildren
could wiggle and chomp and crawl and breathe and squeak and cuddle and grab and hoot and
walk and talk, and I see one of them … right here!
Each stage has its own little phylogenetic tree, with the various descendants of each successive “grandmother” shown as each other's cousins, and there is an overall tree, covering all living things, that anyone (of any age) will find interesting to browse on. Finally, after some 20 pages of simple text and lavish illustration, there are around 4 pages of more detailed information, directed at the adult reading the book, but to which I expect children to return, as they mature, remembering the book with affection, as they surely will, years or even decades later.
So here we have nested families, family resemblance, and the development of more and more specific and complex features. And any adult, or indeed any alert child, will readily extend the discussion. Was there a grandmother cat, whose grandchildren include lions and tigers and pussy-cats, and how was she related to grandmother carnivore? Where do fossils fit in? (The tree shown includes pterodactyls, dinosaurs, and early birds.) And the most common arguments against evolution, from “only a theory” to “where are the intermediate forms?” to “if evolution is true, why are there still monkeys?” will stand immediately revealed as the nonsense they are. Indeed, one of the few statements in the endnotes that I disagree with is that “Evolution by natural selection is very difficult to understand because it doesn't make intuitive sense.” It will, in my opinion, make perfect sense to a child who has met so clear an exposition early on, and who will therefore find it much easier to understand intuitively than, say, Noah's Ark.
Back story: this project was crowdfunded on FaceBook, on the basis of some initial sketches and text. The author professes a long-standing interest in evolution, but his career hitherto has been elsewhere, in computer games (he was lead designer on the 3rd edition of Dungeons and Dragons). However, he has had expert advice from many people, including Eric Meikle, Education Director at the [US] National Center for Science Education.
Publication: pending. Initial partial draft available on request here (technical note: the mammalian tree shown there has since been updated). Diagram from book draft website. Disclosure: I have corresponded with the author who tells me I will be thanked on the book's website. Review based on initial draft + correspondence with author. I will be buying this book for my grandchildren as soon as it becomes available.
The Incredible Unlikeliness of Being, despite (because of?) coming from an established author and presenter, is as personal as could be. It starts with Alice Roberts' emotional response to becoming a mother, and the incredibly unlikely being is the reader. The subject matter is (mainly) the development of the human embryo, and that developing embryo is not some third party abstraction, but you. And so evolution is also about you, as example after example throughout the book makes clear:
It's about your evolutionary heritage, and it is about your own embryological development, when you grew in changed, part of you folding like origami, until you are shaped like a human.… This is the best creation story, because it is true.… This scientific story, pierced together from many different sources of evidence, is more extraordinary, more bizarre, more beautiful, than any creation myth we could have dreamt up.
Alice Roberts is Professor of Public Engagement in Science at the University of Birmingham, and one of the new generation of writers and TV presenters who in the UK fill much the same role as Bill Nye and Neil deGrassie Tyson in the US. She is by training a doctor and anatomist, and much of her own research has involved forensic examination of pre-human hominin skeletons, the coldest of “cold cases”. This background shows up clearly in her detailed descriptions of your developing structures, and she shares with us her emotions about coming face-to-face (in one case literally) with her own anatomy, as when, after x-ray tomography, she was given a replica of her own skull.
Prof Alice Roberts holding a replica of a skull (not, in this case, her own)
The unlikeliness is not just the obvious unlikeliness of your two particular parents meeting, of that one egg becoming fertilised, and of that one sperm out of the enormous number available on being successful. Nor even of the improbability of your parents in turn having come into existence, and so on. Behind all this, and multiplying all those improbabilities, is the meandering history of our evolution:
The more I delve into the structure and workings of the human body, the more I realise what a cobbled-together hodge-podge of bits and pieces this thing we inhabit really is. It is brilliant, but it is also flawed. Our evolutionary history is woven into our embryological development and even adult anatomy in surprising ways; many of our body's flaws can only understood in an evolutionary context.
We start with a history of ideas, and here it struck me as remarkable how long it took for it to be generally recognised that both parents contribute to the form of their offspring, despite the obvious evidence from physical resemblances. Leeuwenhoek with his microscope first observing sperm, the much later discovery of the mammalian ovum, a comical (in hindsight) controversy between “spermists” and “ovists”, the puzzle, insoluble even in principle until the advent of genetics, of how both parents could contribute to what we now call the information content of their offspring, and the further conundrum, unsolved until DNA was identified as the genetic material, of the material means by which they did so.
Most of the book is concerned with the complex process that leads from first release of the ovum, through fertilisation, implantation, and the many subsequent stages of development, through to birth. This story is inextricably intertwined with the story of your evolution, and I can only pick out a few of the most salient points from a wealth of fascinating detail.
From cell division to implantation, with the cells beginning to form separate layers
There are, of course, vestigial or discarded organs. In your second week of development, when you were not much more than a couple of layers of cells, you generated a yolk sac, homologous with the yolk sac of fish, amphibians, reptiles, and even those mammals (the platypus and the spiny anteater) that lay eggs. The difference is that in these the yolk sac is filled with the nourishment that will sustain the growing animal until its birth, whereas in placental mammals like us, it has been without function for the past 90 million years or so. Nonetheless, the recipe for making it has never been deleted from your assembly instructions.
At an early stage, it is very difficult to distinguish the embryo of a mammal (that includes you, of course) from that of a fish; a little later it is still difficult to distinguish it from a reptile or a bird, and different mammalian embryos continue to resemble each other for even longer. For a while, it was suggested that this is because you were retracing your evolutionary history, but we now know that this idea is based on a mistaken model of evolution. You are not more highly evolved, than, say, a chicken; you have just evolved in a different direction. The earliest stages of development are shared with fish, later stages with reptiles and birds, and later stages yet only with mammals and eventually only with our fellow apes. Thus we do not, strictly speaking, recapitulate our evolution from a fish, nor should we, since the present-day fish is as remote as you are from your last common ancestor with a halibut, but we do recapitulate shared development until the parting of the ways. The new science of “evo-devo” is now beginning to take this story down to the most fundamental level, identifying the molecular basis for the parts of the construction plan that you share with a fish, and the parts, activated later, that you do not.
The cartilage base of human skull resembles that of other mammals. It is only later, when this is being transformed to bone, that it acquires its specifically human form, with the enlarged dome required to house the brain towering above the rest of the head.
Working down from the head takes us to the larynx, and the unanswered question of the origin of human speech. Here the problem is that the really important working parts – the larynx itself, its associated muscles, and, above all, the tongue – are soft tissues and leave no trace in the fossil record. The position of the larynx lower in the throat, compared with other mammals, may be no more than an accidental consequence of the way our oversized brainboxes sit on top of our spinal column.
The origin of the larynx leads us to the most striking embryological evidence for evolution, namely the direct resemblance between the branchial (gill) bars of fish, and the related structures found, early in development, in terrestrial vertebrates. Then comparative embryology allows us to map our own organs against their fishy counterparts, and to explain some of the more absurd features of our own anatomy.
Our fishy origins are clearest early in development. By week four, the bundle of cells on its way to becoming you has separated into three separate layers, a tube within a tube within a tube. On the outside, ectoderm, which will give rise to your skin; on the inside, endoderm, which will give rise to your digestive tract, from one end to the other, and in between mesoderm, giving rise to a variety of structures. By week five, we can see what will become the backbone, the eye, and the branchial bars in the neck. Each branchial bar has ectoderm on the outside, endoderm inside, and in between a mixture of cells, some from mesoderm and some from neural crest. This in-between layer will develop into a cartilage bar and muscles, and each bar will develop an artery and a nerve.
Land animals and fish have shared much the same developmental instruction manual until this point, but now they begin to diverge. In fish, the branchial arteries accept blood directly from the heart, and the cartilage forms the gill arches. In land animals, development is far more complex. One set of gill muscles becomes larynx muscles, and a nerve that leads to it runs down into the chest, before making its way back up to the top of the throat. Why so? Because the blood vessels that, in fish, run directly between the heart and the gills have become, in land animals, the aorta and main arteries leading from it. And as a consequence, the recurrent laryngeal nerve, as it is called, is trapped beneath the aortic arch when the heart moves downwards, as it does in land animals but not in fishes, and forced to take this convoluted path. Bad design, but an unavoidable consequence of evolutionary history. A creationist with whom I once discussed this suggested that this really was a good design, because it protects the nerve from damage. Tell that to a giraffe.
The first branchial arch gives rise to bones that are part of the jaw joint in reptiles, but in mammals have shifted and shrunk and become two of the bones of the inner ear. And yes, there is an intermediate form, an early mammal with two jaw joints, the outer one thus being made free to move closer to the ear to improve resonance, and, ultimately, to detach itself. Gill flap muscles in the fish end up as face muscles in primates including us, and so on. The cleft between the first and second branchial arch gives rise, in us, to our ears, and to the tubes that connect the middle ear to the throat, thus enabling pressure to equalise.
Descending to the molecular level, these developments are orchestrated by a set of control genes, prominent among them the so-called “homeobox” or Hoxgenes, first discovered in fruit flies, where they regulate the formation of the segments of head, thorax, and abdomen. Similar genes are found in every segmented animal, including us (if you don't think you're segmented, think of your backbone and ribs). This arrangement must be very ancient, since your last common ancestor with a fruit fly was some 800,000,000 years ago, but has undergone elaboration. The fruitfly has 8 Hox genes, lined up in a row, that come into play one after the other. In the lancelet, this has been expanded to 14. At some stage between the lancelet and jawed fishes, the entire genome seems to have doubled and redoubled, so that you have four sets of Hox genes, each on a different chromosome.
Some aspects of this regulatory system are much more flexible than others. All land vertebrates have a spine with the same basic sections: neck, chest, lower back, sacrum, and tail. All mammals have just seven neck vertebrae, whereas the number of tail vertebrae is highly variable, being up to 49 in one species of porpoise, which flexes its tail to swim, while our tail, or coccyx, has only 3 to 5 fused together. This tail can be considered as a vestigial organ, since it is a mere relic of that sported by our monkey-like ancestors, but like many so-called vestigial organs it continues to earn its keep, in this case by acting as an anchor for muscles. Our lower backs have one more vertebra then our chimp cousins, and are less securely held in place, developments thought to be related to our habitual walking on two feet
Relevant to Professor Roberts' own anatomical interests, although less directly so to the question of embryological development, is the detailed history of our limbs. This indicates us to have been truly bipedal as long ago as 3.2 million years ago (Lucy), while long legs at 1.5 million years ago (Narikotome boy) suggest adaptation for running. In popular imagination, we learned to stand upright as we evolved away from knuckle-walking ancestors, but the reverse may be the case. Monkeys, like us, have feet far harder and less flexible than those of modern non-human apes, and Prof Roberts speculates that our ancestors were tree walkers. If so, it is the apes, with their prehensile toes, rather than us, who have diverged from the form of our common ancestor.
But once we started walking on the ground, that change in behaviour, which could occur within a group in a single generation, would have suddenly generated a new set of selection pressures in favour of long distance walking and running. This is an activity for which we are superbly adapted, even though only a few groups, such as the Tarahumara in Mexico, still regularly practice it.
The final Chapter reviews our present understanding, and considers our place in nature. Development is controlled, more or less, by DNA, including control genes as well as directly expressed genes. It is not, as Haeckel thought, a true recapitulation, but shows clear echoes of earlier stages – segments, gills, fish hearts, the lancelet brain. Our developmental biology is, to use one of Prof Roberts' many memorable metaphors, a palimpsest.
Similar environmental pressures can give rise to similar adaptations, so that the mammalian ear with its three tiny bones has evolved at least four times in different lineages, while, as hinted above, different ways of moving around including bipedalism may have arisen more than once among our ancestors and their close cousins. But nonetheless, evolution remains unpredictable, if only because changes in the environment are unpredictable. One such change was that triggered by the asteroid that did for the (non-avian) dinosaurs. Selection acts without foresight, and without that asteroid, we would not have had humans (for what it's worth, my own view is that we would have had the intelligent descendants of the velociraptors instead).
Evolution takes place in context, and that context, for a species capable of learning from each other, includes a technology. An innovation in toolmaking could have spread through a group of our ancestors in a single generation, triggering a new set of selection pressures that moulded their hands and bodies to a new set of tasks. We speak of the survival of the fittest, but fitness here refers to the cultural, as well as the natural, environment. And we are more influenced in our lives, and our evolution, by our own culture and its artefacts than any other species.
The book concludes with reflections on our similarities (profound) and differences (striking, yet perhaps more quantitative than qualitative) from other species, our contingent and transitory nature, and our uniqueness both as species and, returning to the starting point, individuals.
There are numerous drawings (Prof Roberts is an award-winning artist), and an extensive bibliography.
A few detailed comments. Prof Roberts shows, early on, a series of drawings copied from Haeckel. Connoisseurs of creationism will recognise this as a deliberate provocation, since creationist writers repeatedly point to alleged shortcomings in these, as reason to ignore the whole of developmental science. Lancelets are shown as sister group to vertebrates; in fact, we are closer to tunicates (the subphylum that includes sea squirts) than we are to lancelets, although tunicates only acquired their sessile habit after we and they had gone our separate ways (Prof Roberts tells me that this will be corrected in later editions. I occasionally found the layout of diagrams and their explanations rather awkward. This may be an inherent limitation of the e-book format that I was using.
Figures from Prof Roberts' personal website, and Amazon website. Disclosure: this review is of the first Kindle edition, personal purchase.
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The Incredible Unlikeliness of Being: Evolution and the Making of Us, by Alice Roberts, Heron; Grandmother Fish, by Jonathan Tweet illust. Karen Lewis, independently published