As you can see, Eomaia was nothing like a chimpanzee and nothing like an elephant. Vaguely like a shrew, it probably was pretty similar to their common ancestor, with which it was roughly contemporary, and you can see that a lot of evolutionary change has taken place along both pathways from an Eomaia- like ancestor to an elephant descendant, and from the same Eomaia- like ancestor to a chimpanzee descendant. But it is not in any sense an elephanzee. If it were, it would also have to be a dogatee, for whatever is the common ancestor of a chimpanzee and an elephant is also the common ancestor of a dog and a manatee. And it would also have to be an aardvapotamus, for the same ancestor is also the common ancestor of an aardvark and a hippopotamus. The very idea of a dogatee (or an elephanzee, or an aardvapotamus or a kangaroceros or a buffalion) is deeply unevolutionary and ridiculous. So is a fronkey, and it is a disgrace that the perpetrator of that little witlessism, the Australian itinerant preacher John Mackay, has been touring British schools in 2008 and 2009, masquerading as a ‘geologist’, teaching innocent children that if evolution were true the fossil record should contain ‘fronkeys’.
Eomaia
An equally ludicrous example is to be found in the Muslim apologist Harun Yahya’s enormous, lavishly produced, glossily illustrated and fatuously ignorant book Atlas of Creation. This book obviously cost a fortune to produce, which makes it all the more astounding that it was distributed free to tens of thousands of science teachers, including me. Notwithstanding the prodigious sums of money spent on this book, the errors in it have become legendary. In the service of illustrating the falsehood that most ancient fossils are indistinguishable from their modern counterparts, Yahya shows a sea snake as an ‘eel’ (two animals so different that they are placed in different classes of vertebrates), a starfish as a ‘brittlestar’ (actually different classes of echinoderms), a sabellid (annelid) worm as a crinoid ‘sea lily’ (an echinoderm: this pair come not just from different phyla but from different sub-kingdoms, so that they could hardly be more distant from each other if they tried, while still both being animals) and – best of all – a fishing lure as a ‘caddis fly’ (see colour page 8).
But in addition to these gems of partisan risibility, the book has a section on missing links. One picture is seriously offered to illustrate the fact that there is no intermediate form between a fish and a starfish. I find it impossible to believe that the author seriously thinks evolutionists would expect to find a transition between two such differing animals as a starfish and a fish. I therefore cannot help suspecting that he knows his audience all too well, and is deliberately and cynically exploiting their ignorance.
‘I’LL BELIEVE IN EVOLUTION WHEN A MONKEY GIVES BIRTH TO A HUMAN BABY’
Once again, humans are not descended from monkeys. We share a common ancestor with monkeys. As it happens, the common ancestor would have looked a lot more like a monkey than a man, and we would indeed probably have called it a monkey if we had met it, some 25 million years ago. But even though humans evolved from an ancestor that we could sensibly call a monkey, no animal gives birth to an instant new species, or at least not one as different from itself as a man is from a monkey, or even from a chimpanzee. That isn’t what evolution is about. Evolution not only is a gradual process as a matter of fact; it has to be gradual if it is to do any explanatory work. Huge leaps in a single generation – which is what a monkey giving birth to a human would be – are almost as unlikely as divine creation, and are ruled out for the same reason: too statistically improbable. It would be so nice if those who oppose evolution would take a tiny bit of trouble to learn the merest rudiments of what it is that they are opposing.
THE PERNICIOUS LEGACY OF THE GREAT CHAIN OF BEING
Underlying much of the fallacious demand for ‘missing links’ is a medieval myth, which occupied men’s minds right up to the age of Darwin and stubbornly confused them after it. This is the myth of the Great Chain of Being, according to which everything in the universe sat on a ladder, with God at the top, then archangels, then various ranks of angels, then human beings, then animals, then plants, then down to stones and other inanimate creations. Given that this goes way back to a time when racism was second nature, I hardly need add that human beings were not all sitting on the same rung. Oh no. And of course males were a healthy rung above females of their kind (which was why I let myself get away with ‘occupied men’s minds’ in the opening sentence of this section). But it was the alleged hierarchy within the animal kingdom that had the greatest capacity to muddy the waters when the idea of evolution burst upon the scene. It seemed natural to suppose that ‘lower’ animals evolved into ‘higher’ animals. And if this were so, we should expect to see ‘links’ between them, all the way up and down the ‘ladder’. A ladder with lots of missing rungs lacks conviction. It is this image of the rungless ladder that lurks behind much of the scepticism about ‘missing links’. But the entire ladder myth is deeply misconceived and un-evolutionary, as I shall now show.
So glibly do the phrases ‘higher animals’ and ‘lower animals’ trip off our tongues that it comes as a shock to realize that, far from effortlessly slotting into evolutionary thinking as one might suppose, they were – and are – deeply antithetical to it. We think we know that chimpanzees are higher animals and earthworms are lower, we think we’ve always known what that means, and we think evolution makes it even clearer. But it doesn’t. It is by no means clear that it means anything at all. Or if it means anything, it means so many different things as to be misleading, even pernicious.
Here is a list of the more or less distinctly confusing things you might mean when you say, for example, that a monkey is ‘higher’ than an earthworm.
1 ‘Monkeys evolved from earthworms.’ This is false, just as it is false that humans evolved from chimpanzees. Monkeys and earthworms share a common ancestor.
2 ‘The common ancestor of monkeys and earthworms was more like an earthworm than like a monkey.’ Well, that potentially makes more sense. You can even use the word ‘primitive’ in a semiprecise way, if you define it as ‘resembling ancestors’, and it is obviously true that some modern animals are more primitive in this sense than others. What that exactly means, if you think about it, is that the more primitive of a pair of species has changed less since the common ancestor (all species, without exception, share a common ancestor if you go back far enough). If neither species has changed dramatically more than the other, the word ‘primitive’ should not be used in comparing them.
It’s worth pausing here to make a related point. It is hard to measure degrees of resemblance. And there is in any case no necessary reason why the common ancestor of two modern animals should be more like one than the other. If you take two animals, say a herring and a squid, it is possible that one of them resembles the common ancestor more than the other, but it doesn’t follow that this has to be the case. There has been an exactly equal amount of time for both to have diverged from the ancestor, so the prior expectation of an evolutionist might be, if anything, that no modern animal should be more primitive than any other. We might expect both of them to have changed to the same extent, but in different directions, since the time of the shared ancestor. This expectation, as it happens, is often violated (as in the case of monkey and earthworm), but there is no necessary reason why we should expect it to be. Moreover, the different parts of animals don’t all have to evolve at the same rate. An animal might be primitive from the waist down but highly evolved from the waist up. Less facetiously, one of them might be more primitive in its nervous system, the other more primitive in its skeleton. Notice especially that ‘primitive’ in the sense of ‘resembling ancestors’ does not have to go with ‘simple’ (meaning less complex). A horse’s foot is simpler than a human foot (it has only a single digit instead of five, for example), but the human foot is more primitive (the ancestor that we share with horses had five digits, as we do, so the horse has changed more). This leads us on to the next item in our list.
3 ‘Monkeys a
re cleverer [or prettier, have larger genomes, more complicated body plans, etc. etc.] than earthworms.’ This kind of zoological snobbery is a mess when you start trying to apply it scientifically. I mention it only because it is so readily confused with the other meanings, and the best way to sort out confusion is to expose it. You could imagine a large number of scales along which you might rank animals – not just the four scales I have mentioned. Animals that are high on one of these ladders may or may not be high on another. Mammals certainly have larger brains than salamanders, but they have smaller genomes than some salamanders.
4 ‘Monkeys are more like humans than earthworms are.’ This is undeniable for the particular example of monkeys and earthworms. But so what? Why should we choose humans as the standard against which we judge other organisms? An indignant leech might point out that earthworms have the great virtue of being more like leeches than humans are. Despite the Great Chain of Being’s traditional ranking of humans between animals and angels, there is no evolutionary justification for the common assumption that evolution is somehow ‘aimed’ at humans, or that humans are ‘evolution’s last word’. It is remarkable how commonly this vainglorious assumption thrusts itself forward. At its crudest level, you meet it in the ubiquitously querulous, ‘If chimps evolved into us, how come there are still chimps around?’ I’ve already mentioned this, and I’m not joking. I meet this question again and again and again, sometimes from apparently well-educated people.*
5 ‘Monkeys [and other ‘higher’ animals] are better at surviving than earthworms [and other ‘lower’ animals].’ This doesn’t even begin to be sensible, or even true. All living species have survived at least into the present. Some monkeys, such as the exquisite golden tamarin, are in danger of going extinct. They are much less good at surviving than earthworms are. Rats and cockroaches flourish, despite being regarded by many people as ‘lower’ than gorillas and orang-utans, which are perilously close to extinction.
I hope I’ve said enough to show what nonsense it is to rank modern species on a ladder, as though it were obvious what you meant by ‘higher’ and ‘lower’, and to show how thoroughly unevolutionary it is. You can imagine lots and lots of ladders; it might sometimes be sensible to rank animals on at least some of the ladders separately, but the ladders are not well correlated with each other, and none of them has any right to be called an ‘evolutionary scale’. We have seen the historical temptation to crude errors such as ‘Why aren’t there any fronkeys?’ But the pernicious legacy of the Great Chain of Being also feeds the challenge ‘Where are the intermediates between major animal groups?’ and, nearly as discreditably, underlies the tendency of evolutionists to answer such a challenge by trotting out particular fossils, such as Archaeopteryx, the celebrated ‘intermediate between reptiles and birds’. Nevertheless, there is something else going on underneath the Archaeopteryx fallacy, and it is of general importance; so I shall give it a couple of paragraphs, using Archaeopteryx as a particular example of a general case.
Zoologists have traditionally divided the vertebrates into classes: major divisions with names like mammals, birds, reptiles and amphibians. Some zoologists, called ‘cladists’,* insist that a proper class must consist of animals all of whom share a common ancestor which belonged to that class and which has no descendants outside that group. The birds would be an example of a good class.† All birds are descended from a single ancestor that would also have been called a bird and would have shared with modern birds the key diagnostic characters – feathers, wings, a beak, etc. The animals commonly called reptiles are not a good class in this sense. This is because, at least in conventional taxonomies, the category explicitly excludes birds (they constitute their own class) and yet some ‘reptiles’ as conventionally recognized (e.g. crocodiles and dinosaurs) are closer cousins to birds than they are to other ‘reptiles’ (e.g. lizards and turtles). Indeed, some dinosaurs are closer cousins to birds than they are to other dinosaurs. ‘Reptiles’, then, is an artificial class, because birds are artificially excluded. In a strict sense, if we were to make reptiles a truly natural class, we should have to include birds as reptiles. Cladistically inclined zoologists avoid the word ‘reptiles’ altogether, splitting them into Archosaurs (crocodiles, dinosaurs and birds), Lepidosaurs (snakes, lizards and the rare Sphenodon of New Zealand) and Testudines (turtles and tortoises). Non-cladistically inclined zoologists are happy to use a word like ‘reptile’ because they find it descriptively useful, even if it does artificially exclude the birds.
But what is it about the birds that tempts us to hive them off from the reptiles? What is it that seems to justify bestowing on birds the accolade of ‘class’, when they are, evolutionarily speaking, just one branch within reptiles? It is the fact that the immediately surrounding reptiles, birds’ close neighbours on the tree of life, happen to be extinct, while the birds, alone of their kind, marched on. The closest relatives of birds are all to be found among the longextinct dinosaurs. If a wide variety of dinosaur lineages had survived, birds would not stand out: they would not have been elevated to the status of their own class of vertebrates, and we would not be asking any such question as ‘Where are the missing links between reptiles and birds?’ Archaeopteryx would still be a nice fossil to have in your museum, but it would not play its present starring role as the stock answer to (what we can now see is) an empty challenge: ‘Produce your intermediates.’ If the cards of extinction had fallen differently, there would just be lots of dinosaurs running about, including some feathered, flying, beaked dinosaurs called birds. And indeed, fossilized feathered dinosaurs are now increasingly being discovered, so it is becoming vividly clear that there really is no major ‘Produce your missing link!’ challenge to which Archaeopteryx is the reply.
Let’s proceed, now, to some of the major transitions in evolution, where ‘links’ have been alleged to be ‘missing’.
UP FROM THE SEA
Short of rocketing into space, it is hard to imagine a bolder or more life-changing step than leaving the water for dry land. The two life-zones are different in so many ways that moving from one to the other demands a radical shift in almost all parts of the body. Gills that are good at extracting oxygen from water are all but useless in air, and lungs are useless in water. Methods of propulsion that are speedy, graceful and efficient in water are dangerously clumsy on land, and vice versa. No wonder ‘fish out of water’ and ‘like a drowning man’ have both become proverbial phrases. And no wonder ‘missing links’ in this region of the fossil record are of more than ordinary interest.
If you go back far enough, everything lived in the sea – watery, salty alma mater of all life. At various points in evolutionary history, enterprising individuals from many different animal groups moved out on to the land, sometimes eventually to the most parched deserts, taking their own private sea water with them in blood and cellular fluids. In addition to the reptiles, birds, mammals and insects we see all around us, other groups that have succeeded in making the great trek out of life’s watery womb include scorpions, snails, crustaceans such as woodlice and land crabs, millipedes and centipedes, spiders and their kin, and at least three phyla of worms. And we mustn’t forget the plants, onlie begetters of usable carbon, without whose prior invasion of the land none of the other migrations could have happened.
Fortunately the transitional stages of our exodus, as fish emerged on to the land, are beautifully documented in the fossil record. So are the transitional stages going the other way much later, as the ancestors of whales and dugongs forsook their hard-won home on dry land and returned to their ancestral seas. In both cases, links that once were missing now abound and grace our museums.
When we say that ‘fish’ emerged on to the land, we have to remember that ‘fish’, like ‘reptiles’, do not constitute a natural group. Fish are defined by exclusion. Fish are all the vertebrates except those that moved on to the land. Because all the early evolution of vertebrates took place in water, it is not surprising that mos
t of the surviving branches of the vertebrate tree are still in the sea. And we still call them ‘fish’ even when they are only distantly related to other ‘fish’. Trout and tuna are closer cousins to humans than they are to sharks, but we call them all ‘fish’. And lungfish and coelacanths are closer cousins to humans than they are to trout and tuna (and of course sharks) but, again, we call them ‘fish’. Even sharks are closer cousins to humans than they are to lampreys and hagfish (the only modern survivors of the once thriving and diverse group of jawless fishes) but again, we call them all fish. Vertebrates whose ancestors never ventured on to land all look like ‘fish’, they all swim like fish (unlike dolphins, which swim with an up-and-down bending of the spine instead of side to side like a fish), and they all, I suspect, taste like fish.
To an evolutionist, as we just saw in the example of reptiles and birds, a ‘natural’ group of animals is a group all of whose members are closer cousins to each other than they are to all non-members of the group. ‘Birds’, as we saw, are a natural group, since they share a most recent common ancestor that is not shared by any non-bird. By the same definition, ‘fish’ and ‘reptiles’ are not natural groups. The most recent common ancestor of all ‘fish’ is shared by many non-fish too. If we push our distant cousins the sharks to one side, we mammals belong to a natural group that includes all modern bony fish (bony as opposed to cartilaginous sharks). If we then push to one side the bony ‘ray-finned fishes’ (salmon, trout, tuna, angel fish: just about all the fish you are likely to see that are not sharks), the natural group to which we belong includes all land vertebrates plus the so-called lobe-finned fishes. It is from the ranks of the lobe-finned fishes that we sprang, and we must now pay special attention to the lobefins.
The Greatest Show on Earth Page 16