The Greatest Show on Earth (13 page)

Lingulella
– almost identical to its modern relatives

Many of the problems that we meet in evolutionary argumentation arise only because animals are inconsiderate enough to evolve at different rates, and might even be inconsiderate enough not to evolve at all. If there were a law of nature dictating that quantity of evolutionary change must always be obligingly proportional to elapsed time, degree of resemblance would faithfully reflect closeness of cousinship. In the real world, however, we have to contend with evolutionary sprinters like birds, who leave their reptile origins standing in the Mesozoic dust – helped, in our perception of their uniqueness, by the happenstance that their neighbours in the evolutionary tree were all killed by a celestial catastrophe. At the other extreme, we have to contend with ‘living fossils’ like Lingula which, in extreme cases, have changed so little that they might almost interbreed with their remote ancestors, if only a matchmaking time-machine could procure them a date.
Lingula is not the only famous example of a living fossil. Others include Limulus, the horseshoe ‘crab’, and coelacanths, which we shall meet in the next chapter.

* Think of it like this. Imagine all possible straight lines. For each line, calculate how closely it fits the dots, by measuring the distance of each dot from the line, and adding up all the distances (after squaring them, for a good mathematical reason which would take us too far afield). Of all possible straight lines, the one that minimizes the sum of the squared dot-to-line distances, summed over all the dots, is the fitted regression line. It shows us the trend, without our eyes being distracted by all the mess of the individual points. There are separate calculations that statisticians do to calculate how reliable the line is as an indicator of a trend. These are called tests of statistical significance. They make use of the breadth of scatter about the line.

* Up to twice as long if the Pod Kopiste lizards have been evolving at the same rate since the shared ancestor of thirty-seven years ago.

* The same gorilla-like features in the skull and teeth of our robust cousin Paranthropus boisei (‘nutcracker man’, also nicknamed ‘Zinj’ and ‘Dear Boy’) indicate that it was almost certainly vegetarian.

* That’s no idle metaphor, for fairy rings of mushrooms achieve their circular form for exactly the same reason.

* You remember the straight line that was the best fit to the data on the decline of elephant tusk size from 1925 to 1958? I explained the method as equivalent to trying all possible straight lines and finding the one that minimized the sum of squares of distances of dots on the graph from the line. But you can do the same thing while not limiting yourself to straight lines. You can look at all possible curves of a certain type defined by mathematicians. The hyperbola is one such curve. In this case, we look at all possible hyperbolas in turn, measure the distance to the line of every point on the graph, then add up the sum of the squared distances over all points. Do the same for all hyperbolas, and then choose the hyperbola that minimizes that sum. Lenski did a sort of short-cut equivalent to that exhaustive operation to arrive at the best-fit hyperbola, which is the one you see drawn in.

* A stepwise pattern of evolution is to be expected in creatures such as bacteria, which (most of the time) don’t reproduce sexually. In animals like us, who reproduce only sexually, evolutionary change doesn’t usually ‘hang about’ while it ‘waits’ for a key mutation to turn up (this is a common mistake made by opponents of evolution with some pretensions to sophistication). Instead, sexually reproducing populations usually have a ready supply of genetic variation from which to select. Although originally generated by past mutation, a large number of genetic variants are often present in a gene pool at any one time, introduced by mutation a while back and now shuffled about by sexual recombination. Natural selection often acts to shift the balance of existing variation, rather than waiting for key mutations to turn up. In bacteria without sexual reproduction, the very idea of a gene pool doesn’t properly apply. That is why we can realistically hope to see discrete steps, where we might not in a population of birds, mammals or fish.

MISSING LINK? WHAT DO YOU MEAN, ‘MISSING’?

CREATIONISTS are deeply enamoured of the fossil record, because they have been taught (by each other) to repeat, over and over, the mantra that it is full of ‘gaps’: ‘Show me your “intermediates”!’ They fondly (very fondly) imagine that these ‘gaps’ are an embarrassment to evolutionists. Actually, we are lucky to have any fossils at all, let alone the massive numbers that we now do have to document evolutionary history – large numbers of which, by any standards, constitute beautiful ‘intermediates’. I shall emphasize in Chapters 9 and 10 that we don’t need fossils in order to demonstrate that evolution is a fact. The evidence for evolution would be entirely secure, even if not a single corpse had ever fossilized. It is a bonus that we do actually have rich seams of fossils to mine, and more are discovered every day. The fossil evidence for evolution in many major animal groups is wonderfully strong. Nevertheless there are, of course, gaps, and creationists love them obsessively.
Let’s again make use of our analogy of the detective coming to the scene of a crime to which there were no eye witnesses. The baronet has been shot. Fingerprints, footprints, DNA from a sweat stain on the pistol, and a strong motive all point towards the butler. It’s pretty much an open and shut case, and the jury and everybody in the court is convinced that the butler did it. But a last-minute piece of evidence is discovered, in the nick of time before the jury retires to consider what had seemed to be their inevitable verdict of guilty: somebody remembers that the baronet had installed spy cameras against burglars. With bated breath, the court watches the films. One of them shows the butler in the act of opening the drawer in his pantry, taking out a pistol, loading it, and creeping stealthily out of the room with a malevolent gleam in his eye. You might think that this solidifies the case against the butler even further. Mark the sequel, however. The butler’s defence lawyer astutely points out that there was no spy camera in the library where the murder took place, and no spy camera in the corridor leading from the butler’s pantry. He wags his finger, in that compelling way that lawyers have made their own. ‘There’s a gap in the video record! We don’t know what happened after the butler left the pantry. There is clearly insufficient evidence to convict my client.’
In vain the prosecution lawyer points out that there was a second camera in the billiard room, and this shows, through the open door, the butler, gun at the ready, creeping on tiptoe along the passage towards the library. Surely this plugs the gap in the video record? Surely the case against the butler is now unassailable? But no. Triumphantly the defence lawyer plays his ace. ‘We don’t know what happened before or after the butler passed the open door of the billiard room. There are now two gaps in the video record. Ladies and gentlemen of the jury, my case rests. There is now even less evidence against my client than there was before.’
The fossil record, like the spy camera in the murder story, is a bonus, something that we had no right to expect as a matter of entitlement. There is already more than enough evidence to convict the butler without the spy camera, and the jury were about to deliver a guilty verdict before the spy camera was discovered. Similarly, there is more than enough evidence for the fact of evolution in the comparative study of modern species (Chapter 10) and their geographical distribution (Chapter 9). We don’t need fossils – the case for evolution is watertight without them; so it is paradoxical to use gaps in the fossil record as though they were evidence against evolution. We are, as I say, lucky to have fossils at all.
What would be evidence against evolution, and very strong evidence at that, would be the discovery of even a single fossil in the wrong geological stratum. I have already made this point in Chapter 4. J. B. S. Haldane famously retorted, when asked to name an observation that would disprove the theory of evolution, ‘Fossil rabbits in the Precambrian!’ No such rabbits, no authentically anachronistic fossils of any kind, have ever been found. All the fossils that we have, and there are very very many indeed, occur, without a single authenticated exception, in the right temporal sequence. Yes, there are gaps, where there are no fossils at all, and that is only to be expected. But not a single solitary fossil has ever been found before it could have evolved. That is a very telling fact (and there is no reason why we should expect it on the creationist theory). As I briefly mentioned in Chapter 4, a good theory, a scientific theory, is one that is vulnerable to disproof, yet is not disproved. Evolution could so easily be disproved if just a single fossil turned up in the wrong date order. Evolution has passed this test with flying colours. Sceptics of evolution who wish to prove their case should be diligently scrabbling around in the rocks, desperately trying to find anachronistic fossils. Maybe they’ll find one. Want a bet?
The biggest gap, and the one the creationists like best of all, is the one that preceded the so-called Cambrian Explosion. A little more than half a billion years ago, in the Cambrian era, most of the great animal phyla – the main divisions within the animal world – ‘suddenly’ appear in the fossil record. Suddenly, that is, in the sense that no fossils of these animal groups are known in rocks older than the Cambrian, not suddenly in the sense of instantaneously: the period we are talking about covers about 20 million years. Twenty million years feels short when it is half a billion years ago. But of course it represents exactly the same amount of time for evolution as 20 million years today! Anyway, it is still quite sudden, and, as I wrote in a previous book, the Cambrian shows us a substantial number of major animal phyla
already in an advanced state of evolution, the very first time they appear. It is as though they were just planted there, without any evolutionary history. Needless to say, this appearance of sudden planting has delighted creationists.
That last sentence shows that I was savvy enough to realize that creationists would like the Cambrian Explosion. I was not (back in 1986) savvy enough to realize that they’d gleefully quote my lines back at me in their own favour, over and over again, carefully omitting my careful words of explanation. On a whim, I just searched the World Wide Web for ‘It is as though they were just planted there, without any evolutionary history’ and obtained no fewer than 1,250 hits. As a crude control test of the hypothesis that the majority of these hits represent creationist quote-minings, I tried searching, as a comparison, for the clause that immediately follows the above quotation in The Blind Watchmaker: ‘Evolutionists of all stripes believe, however, that this really does represent a very large gap in the fossil record’. I obtained a grand total of 63 hits, compared to the 1,250 hits for the previous sentence. The ratio of 1250 to 63 is 19.8. We might call this ratio the Quote Mining Index.
I have dealt with the Cambrian Explosion at length, especially in Unweaving the Rainbow. Here I’ll add just one new point, illustrated by the flatworms, Platyhelminthes. This great phylum of worms includes the parasitic flukes and tapeworms, which are of great medical importance. My favourites, however, are the free-living turbellarian worms, of which there are more than four thousand species: that’s about as numerous as all the mammal species put together. Some of these turbellarians are creatures of great beauty, as the two pictured opposite show. They are common, both in water and on land, and presumably have been common for a very long time. You’d expect, therefore, to see a rich fossil history. Unfortunately, there is almost nothing. Apart from a handful of ambiguous trace fossils, not a single fossil flatworm has ever been found. The Platyhelminthes, to a worm, are ‘already in an advanced state of evolution, the very first time they appear. It is as though they were just planted there, without any evolutionary history.’ But in this case, ‘the very first time they appear’ is not the Cambrian but today. Do you see what this means, or at least ought to mean for creationists? Creationists believe that flatworms were created in the same week as all other creatures. They have therefore had exactly the same time in which to fossilize as all other animals. During all the centuries when all those bony or shelly animals were depositing their fossils by the thousands, the flatworms must have been living happily alongside them, but without leaving any significant trace of their presence in the rocks. What, then, is so special about gaps in the record of those animals that do fossilize, given that the past history of the flatworms amounts to one big gap: even though the flatworms, by the creationists’ own account, have been living for the same length of time? If the gap before the Cambrian Explosion is used as evidence that most animals suddenly sprang into existence in the Cambrian, exactly the same ‘logic’ should be used to prove that the flatworms sprang into existence yesterday. Yet this contradicts the creationist’s belief that flatworms were created during the same creative week as everything else. You cannot have it both ways. This argument, at a stroke, completely destroys the creationist case that the Precambrian gap in the fossil record weakens the evidence for evolution.

Turbellarians – no fossil record, but they must have been there all along

Why, on the evolutionary view, are there so few fossils before the Cambrian era? Well, presumably, whatever factors applied to the flatworms throughout geological time to this day, those same factors applied to the rest of the animal kingdom before the Cambrian. Probably, most animals before the Cambrian were soft-bodied like modern flatworms, probably also rather small like modern turbellarians – just not good fossil material. Then something happened half a billion years ago to allow animals to fossilize freely – the arising of hard, mineralized skeletons, for example.
An earlier name for ‘gap in the fossil record’ was ‘missing link’. The phrase enjoyed a vogue in late Victorian England, and persisted into the twentieth century. Inspired by a misunderstanding of Darwin’s theory, it was used as an insult in roughly the same way as ‘neanderthal’ is colloquially (and unjustly) used today. Among the Oxford English Dictionary’s list of representative quotations is a 1930 one in which D. H. Lawrence tells of a woman who wrote to say his name ‘stank’ and went on, ‘You, who are a mixture of the missing-link and the chimpanzee.’
The original meaning, a confused one as I shall show, implied that the Darwinian theory lacked a vital link between humans and other primates. Another of the dictionary’s illustrative quotations, a Victorian one, uses it like this: ‘I’ve heard talk o’ some missing link, atween men and puggies’ (‘puggie’ was a Scottish dialect word for monkey). History-deniers, to this day, are very fond of saying, in what they imagine is a taunting tone of voice: ‘But you still haven’t found the missing link,’ and they often throw in a jibe about Piltdown Man, for good measure. Nobody knows who perpetrated the Piltdown hoax, but he has a lot to answer for.* The fact that one of the first candidates for a man-ape fossil to be discovered turned out to be a hoax provided an excuse for history-deniers to ignore the very numerous fossils that are not hoaxes; and they still haven’t stopped crowing about it. If only they would look at the facts, they’d soon discover that we now have a rich supply of intermediate fossils linking modern humans to the common ancestor that we share with chimpanzees. On the human side of the divide, that is. Interestingly, there are as yet no fossils linking that ancestor (which was neither chimpanzee nor human) to modern chimpanzees. Perhaps this is because chimpanzees live in forests, which don’t provide good fossilizing conditions. If anything it is chimpanzees, not humans, who today have a right to complain of missing links!
That, then, is one meaning of ‘missing link’. It is the alleged gap between humans and the rest of the animal kingdom. The missing link in that sense is, to put it mildly, no longer missing. I shall return to this in the next chapter, which is specifically about human fossils.
Another meaning concerns the alleged paucity of so-called ‘transitional forms’ between major groups: between reptiles and birds, for example, or between fish and amphibians. ‘Produce your intermediates!’ Evolutionists often respond to this challenge from history-deniers by throwing them the bones of Archaeopteryx, the famous ‘intermediate’ between ‘reptiles’ and birds. This is a mistake, as I shall show. Archaeopteryx is not the answer to a challenge, because there is no challenge worth answering. To put up a single famous fossil like Archaeopteryx panders to a fallacy. In fact, for a large number of fossils, a good case can be made that every one of them is an intermediate between something and something else. The alleged challenge that seems to be answered by Archaeopteryx is based on an outdated conception, the one that used to be known as the Great Chain of Being; and that is the title under which I shall deal with it later in this chapter.
The silliest of all these ‘missing link’ challenges are the following two (or variants of them, of which there are many). First, ‘If people came from monkeys via frogs and fish, then why does the fossil record not contain a “fronkey”?’ I have seen an Islamic creationist ask truculently why there are no crocoducks. And, second, ‘I’ll believe in evolution when I see a monkey give birth to a human baby.’ This last one makes the same mistake as all the others, plus the additional one of thinking that major evolutionary change happens overnight.
As it happens, two of these fallacies crop up next door to each other in the long list of comments that follow an article in the Sunday
Times (London) about a television documentary on Darwin that I presented:Dawkins opinion on religion is absurd since Evolution is nothing more than a religion itself – you have to believe we all came from a single cell . . . and that a snail can become a monkey etc. Ha Ha – that’s the most laughable religion yet!!
Joyce, Warwickshire, UK
Dawkins should explain why science has failed to find the missing links. Faith in unfounded science is more fairy tale stuff than faith in God.
Bob, Las Vegas, USA
This chapter will deal with all these related fallacies, beginning with the silliest of all, since the answer to it will serve as an introduction to the others.