Evolutionary mirror-reading

(Posted on behalf of Steve Hays)

Below are some excerpts from Henry Gee’s book on cladistics. My transcription preserves the original emphases.

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Many of the assumptions we make about evolution, especially concerning the history of life as understood from the fossil record, are, however, baseless. The reason for this lies with the fact of the scale of geological time that scientists are dealing with, which is so vast that it defies narrative. Fossils, such as the fossils of creatures we hail as our ancestors, constitute primary evidence for the history of life, but each fossil is an infinitesimal dot, lost in a fathomless sea of time, whose relationship with other fossils and organisms living in the present day is obscure. Any story we tell against the compass of geological time that links these fossils in sequences of cause and effect—or ancestry and descent—is, therefore, only ours to make. We invent these stories, after the fact, to justify the history of life according to our own prejudices.¹

Fossils are never found with labels or certificates of authenticity. You can never know that the fossil bone you might dig up in Africa belonged to your direct ancestor, or anyone else’s. The attribution of ancestry does not come from the fossil; it can only come from us. Fossils are mute: their silence gives us unlimited licence to tell their stories for them, which usually takes the form of chains of ancestry and descent…Such tales are sustained more in our minds than in reality and are informed and conditioned by our own prejudices, which will tell us not what really happened, but what we think ought to have happened. If there are “missing links,” they exist only in our imaginations.²

Once we realize that Deep Time can never support narratives of evolution, we are forced to accept that virtually everything we thought we knew about evolution is wrong…If we can never know for certain that any fossil we unearth is our direct ancestor, it is similarly invalid to pluck a string of fossils from Deep Time, arrange these fossils in chronological order, and assert that this arrangement represents a sequence of evolutionary ancestry and descent. As Stephen Jay Gould has demonstrated, such misleading tales are part of popular iconography: everyone has seen pictures in which a sequence of fossil hominids—members of the human family of species—are arranged in an orderly procession from primitive forms up to modern Man.³

To complicate matters further, such sequences are justified after the fact by tales of inevitable, progressive improvement. For example, the evolution of Man is said to have been driven by improvements in posture, brain size, and the coordination between hand and eye, which led to technological achievements such a fire, the manufacture of tools, and the use of language. But such scenarios are subjective. They can never be tested by experiment, and so they are unscientific. They rely for their currency not on scientific test, but on assertion and the authority of the presentation.⁴

Whether you believe the conventional wisdom that our own species Homo sapiens descended in seamless continuity from the preexisting species Homo erectus depends not on the evidence (because the fossil evidence is moot) but on the deferment of your lack of knowledge to the authority of the presenter or whether the presentation of the evidence resonates with your prejudices.⁵

The story of human interaction with fossils represents an example of how experience and belief have a powerful effect on interpretation and demonstrates why scientific truths can only be temporary. Today, we see fossils as the remains of creatures that once lived. However, this nature is not inherent in the fossils. It is our immersion in a century and half of Darwinian thought, not the fossils themselves, that gives us the capacity to see fossils as kin to things that were once as alive as you or I.⁶

The intervals of time that separate the fossils are so huge that we cannot say anything definite about their possible connection through ancestry and descent.⁷

The conventional portrait of human evolution—and, indeed, of the history of life—tends to be one of lines of ancestors and descendants. We concentrate on the events leading to modern humanity, ignoring or playing down the evolution of other animals: we prune away all branches in the tree of life except the one leading to ourselves. The result, inevitably, is a tale of progressive improvement, culminating in modern humanity. From our privileged vantage point in the present day, we look back at human ancestry and pick out the features in fossil hominids that we see in our selves—a big brain, an upright stance, the use of tools, and so on. Naturally, we arrange fossil hominids in a series according to their resemblance to the human state.⁸

The conventional, linear view easily becomes a story in which the features of humanity are acquired in a sequence that can be discerned retrospectively—first an upright stance, then a bigger brain, then the invention of toolmaking, and so on, with ourselves as the inevitable consequence.⁹

New fossil discoveries are fitted into this preexisting story. We call these new discoveries “missing links,” as if the chain of ancestry and descent were a real object for our contemplation, and not what it really is: a completely human invention created after the fact, shaped to according with human prejudices. In reality…each fossil represents an isolated point, with no knowable connection to any other given fossil, and all float around in an overwhelming sea of gaps.¹⁰

Just because the unicorn looks something like a bull or a horse to us, this does not imply that a unicorn is a missing link between these two animals. Horses and bulls are contingent; they just happened to offer themselves as models because they are familiar and available. Perhaps in another part of the world, a unicorn would be seen as a mixture of a camel and a kudu, but a unicorn would not be a missing link between those animals either.¹¹

This task had very little to do with what the fishes were like as living animals. All I had were fragments that I could link to larger and more certainly known fragments that were sufficiently informative to have a name. I might as well have been doing the same thing with stamps, or cigarette cards. The relationships that these fishes had with living animals is so distant that any attempt to clothe them in flesh, to make them swim, requires a leap of faith.¹²

However, this leap must in some degree be fuelled by comparison with the animals that live around us today. If this were not possible, we would not be able to make any sense of fossils at all. When we look at pteraspids now, we interpret them in terms of lampreys: that is how they “make sense” to us. But the model of a pteraspid in terms of a lamprey is as provisional as that which once linked pteraspids with squid.¹³

The quest to interpret fossils in terms of modern models rests on the assumption that all life on Earth has a common ancestry, because we can interpret past life only in terms of other living organisms. If this were not possible, we would not recognize the fossils of animals as animals at all. We’d just see them as rocks.¹⁴

Crucially, you should have a clear idea about the position of the organism in nature before speculating about the function of its various parts. Let me explain. Let’s say that you have discovered that unicorns use their horns to kill dragons. Using this information, you could spin a tale about the importance of the horn in unicorn evolution: unicorns evolved in dragon country, where possession of horns was an asset. Unicorns without horns would all be charred to ashes by the fire-breathing dragons. Only those unicorns with horns survived to perpetuate the species.¹⁵

This story sounds plausible, but like the story about the evolution of tetrapod limbs, it cannot be tested. What is more, if you use your prior (and untestable) assumption that the unicorn evolved its horn to kill dragons as a guide to the unicorn’s relationships, you cannot then use this information in any subsequent test of the function of the unicorn’s horn. Why? Because you have already assumed that you know the horn’s function, even before you run the test. You have loaded the dice to tell you what you want.¹⁶

Misinterpretations about “adaptive purpose” ignore the fact that natural selection is a blind and undirected consequence of the interaction between variation and the environment. Natural selection exists only in the continuous present of the natural world: it has no memory of its previous actions, no plans for the future, or underlying purpose. It is not a winnowing force with an independent existence that can b e personified, like Death, with his black cowl and scythe.¹⁷

Artificial selection is an imperfect metaphor for natural selection because breeders quite obviously do have intelligible reasons for why they select some traits and not others. Unlike natural selection, breeders have memories, plans, and purposes. They select for the same traits, generation after generation, to produce a discernible trend. Natural selection could hardly be more different¹⁸

To take a line of fossils and claim that they represent a linage is not a scientific hypothesis that can be tested, but an assertion that carries the same validity as a bedtime story—amusing, perhaps even instructive, but not scientific.¹⁹

Ornithologists, who study modern birds, regard Archaeopteryx as an ancestor and an icon. Given that they have already judged where Archaeopteryx fits into the history of life, they look at the fossil and see exactly what they expect to find—birdlike features…Archaeopteryx has feathers, so it is a bird by definition. Its archaisms are only to be expected, given the fossil’s great antiquity when compared with other bird fossils. Because they study modern birds, ornithologists will, naturally, tend to see bird evolution in terms of perceived adaptations to birds’ current, airborne niche.²⁰

Palaeontologists, in contrast, come to Archaeopteryx with a different search image…To palaeontologists, Archaeopteryx looks very similar to members of a group of dinosaurs called theropods….In this light, palaeontologists tends to see the feathers of Archaeopteryx as intriguing decorations for the body of a theropod dinosaur, not as central, key features essential for explaining the course of evolution in birds.²¹

The finds are 4.4 million years old and come from a place called Aramis. “This is the earliest-known hominid,” says White, proudly, but with a touch of self-deprecating humour that demonstrates a sensitivity to the inevitably piecemeal nature of human fossil remains, in which all the evidence for the hominid lineage between about 10 and 5 million years ago—several thousand generations of living creatures—can be fitted into a small box.²²

There is therefore nothing special, advanced, or progressive about bipedality—only the fact that it is we who are bipedal, and it is we who are writing the book, makes it so.²³

To complicate matters, brain volume can vary enormously among individuals in a species, with no discernible connection to intelligence.²⁴

1 In Search of Deep Time: Beyond the Fossil Record to a New History of Life (Cornell 2001), 1-2.

2 Ibid. 2.

3 Ibid. 4-5.

4 Ibid. 5.

5 Ibid. 8.

6 Ibid. 9.

7 Ibid. 23.

8 Ibid. 32.

9 Ibid. 32.

10 Ibid. 32.

11 Ibid. 54.

12 Ibid. 61.

13 Ibid. 61.

14 Ibid. 82.

15 Ibid. 87-88.

16 Ibid. 88.

17 Ibid. 96.

18 Ibid. 96-97.

19 Ibid. 117-18.

20 Ibid. 180.

21 Ibid. 180-81.

22 Ibid. 201-02.

23 Ibid. 214.

24 Ibid. 214.