Tuesday, April 13, 2010

"Overwhelming evidence for evolution"

According to the OT scholar, Bruce Waltke:

If the data is overwhelmingly in favor of evolution, to deny that reality will make us a cult…some odd group that is not really interacting with the world. And rightly so, because we are not using our gifts and trusting God’s Providence that brought us to this point of our awareness.


But according to Henry Gee, paleontologist, evolutionary biologist, and a senior editor of Nature:

Fossils are where you find them, not where you want them. They are not found spread uniformly through the Earth's sediments. They are granted to posterity only thanks to accidents of geology.

The question immediately presented itself: could this fossil have belonged to a creature that was my direct ancestor?

It is possible, of course, that the fossil really did belong to my lineal ancestor. Everybody has an ancestry, after all. Given what the Leakeys and others have found in East Africa, there is good reason to suspect that hominids lived in the Rift before they lived anywhere else in the world, so all modern humans must derive their ancestry, ultimately, from this spot, or somewhere near it. It is therefore reasonable to suppose that we should all be able to trace our ancestries, in a general way, to creatures that lived in the Rift between roughly 5 and 3 million years ago. So much is true, but it is impossible to know, for certain, that the fossil I hold in my hand is my lineal ancestor. Even if it really was my ancestor, I could never know this unless every generation between the fossil and me had preserved some record of its existence and its pedigree. The fossil itself is not accompanied by a helpful label. The truth is that my own particular ancestry — or yours — may never be recovered from the fossil record.

The obstacle to this certain knowledge about lineal ancestry lies in the extreme sparseness of the fossil record. As noted above, if my mystery skull belonged to an extinct giant civet, Pseudocivetta ingens, it would be the oldest known record of this species by a million years. This means that no fossils have been found that record the existence of this species for that entire time; and yet the giant civets must have been there all along. Depending on how old giant civets had to be before they could breed (something else we can never establish, because giant civets no longer exist so that we can watch their behaviour), perhaps a hundred thousand generations lived and died between the fossil found by me at site LO5 and the next oldest specimen. In addition, we cannot know if the fossil found at LO5 was the lineal ancestor of the specimens found at Olduvai Gorge or Koobi Fora. It might have been, but we can never know this for certain. 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.

In our everyday experience, on the scale of days and years, events can be ordered in time with a fair degree of certainty. We can be confident about what is cause and what is effect, and that one can be linked with another. In our everyday experience, individual events can be linked together to form a continuous narrative. You can see this to be true by looking back at your own working day.

Our perception of time changes when events become progressively divorced from the chronological context of our everyday experience. For example, look back at your family photograph albums. Photographs taken in the past few years are full of meaning for you. You can remember who is who in the picture, when and where the picture was taken, and even what was said at the time: your engagement with the picture is enriched by its context, the interconnecting web of events that connect that one snapshot with a whole host of other events, to make a story, part of the ongoing narrative of your life.

Now look at older photographs, perhaps from that vacation you had a few years ago. The enjoyment of vacations, so vivid at the time, is soon lost when you get back to the humdrum routine of home. You get the snapshots developed; you had always meant to label them while the memories were still fresh, but you never got around to it. Now, years later, it's too late — you can't quite remember who is in the pictures, exactly where they were taken, or in which order. Even the year escapes you unless you have some independent means of recalling it: the year the baby took her first steps, the year we bought the new car, and so on.

Turn the pages, back and further back, until there are no more pages, and all you have is a box of unmounted photographs left to you in the will of a remote great-uncle. None of your own experience allows you even to put these photographs in the correct chronological order. The pictures are of long-dead relations you have never met, and of whose existence you were previously unaware.

When confronted with such an image, no connection of shared events — of narrative — exists between you and the person in the photograph. The event depicted in the picture is lost in time, free from any context that might tie it to the present. When the fading of memory dulls the skein of your experience, it becomes difficult to arrange isolated events of your own life, as recorded by family snapshots, in any reliable order. When the life concerned is not your own, but that of another — a person who lived a long time ago in a foreign country — the task becomes impossible, especially when that person is dead and cannot be interviewed.

Looking back further still, we can see that our knowledge of past history — by implication, a narrative — is determined by the density, connectedness, and context of events. If events are isolated and disconnected, history breaks down. Students of ancient history, or of more recent intervals such as the Dark Ages in Britain, for example, have problems simply working out the order in which things happened, such as which king reigned before which. These problems are worsened by sparseness of documentation, of context. Between 410 ad, when the Romans quit Britain, and 597 ad, when Augustine arrived on the coast of Kent, there are few events in British history that can be treated as fact rather than conjecture. This is an interval of time equivalent in length to that between the Napoleonic Wars and the present day. No wonder, therefore, that this period is full of myth and legend: all sense of connected history and the passage of time ceases, filled instead with the timeless and retrospective romances of King Arthur and the Knights of the Round Table.

The disconnection and isolation of events worsens further as centuries turn into millennia, tens of millennia, and finally into millions of years: intervals so vast that they dwarf the events within them. Events become disconnected, separated like stars by gulfs of space measurable not in miles, but in light-years. This is geological time, far beyond everyday human experience.

This is Deep Time.

Deep Time is like an endless, dark corridor, with no landmarks to give it scale. This darkness is occasionally pierced by a shaft of light from an open door. Peering into the lighted room, we see a tableau of unfamiliar characters from the lost past, but we are unable to connect the scene before us with that encountered in any other room in the corridor of time, or with our own time. Deep Time is fragmented, something qualitatively different from the richly interwoven tapestry of time afforded by our everyday experience, what I call 'everyday time' or 'ordinary time'.

A fossil can be thought of as an event in Deep Time. Compared with the immensity of time in which it is found, a fossil is a point in time of zero extent: a fossil either exists or it doesn't. By itself, a fossil is a punctuation mark, an interjection, an exclamation, even, but it is not a word, or even a sentence, let alone a whole story. Fossils are the tableaux that are illuminated by the occasional shafts of light that punctuate the corridor of Deep Time. You cannot connect one fossil with any other to form a narrative.

So there I was, confronted with a fossil that might have been half a tooth of a hominid, a scrap of flotsam from the ocean of time. Let us give a name — Yorick -- to its deceased owner. Yorick might have been my lineal ancestor; but we can never establish this for certain.

The events of Deep Time — fossils — are so sparse, because an animal, once dead, only rarely becomes a fossil. A million years passed between one fossil of Pseudocivetta ingens and the next. The process of fossilization and discovery is a concatenation of chance built upon chance. It's amazing that anything ever becomes a fossil at all.

Yorick could have been a member of the species Australopithecus afarensis, by default, simply because we know of no other hominids living in East Africa at that time. But there's an old saying in science: absence of evidence isn't evidence of absence. Yorick could have belonged to some other species entirely. The half-tooth could be the first record of this species and, so far, the only record that this species ever existed. Imagine — an entire species can evolve, thrive, decline, and disappear and leave just half a tooth as a memorial to its existence. You can only wonder how many species have come and gone, leaving no record at all.

The fact is that we know so little of the past. We depend on the minute fraction of the life that Earth has produced that has left any record. We have hardly begun to count the species with which we share this planet, yet for every species now living, perhaps a thousand, or a million, or a thousand million (we will never know for certain) have appeared and become extinct.

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 accord with human prejudices. In reality, the physical record of human evolution is more modest. 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.

The problem is that Fred and I cannot place our common ancestor in time and space unless we are able to discover our complete pedigrees all the way back to that point of ancestral convergence. To do this, as we know, is impossible, given that the fossil record is so discontinuous.

If it's possible to arrange three participants in more than one way, how can one know which one reflects the actual course of evolution — what really happened? The cladogram in figure 3 seems so natural, so plausible, that it must be right. But must it? The fact that three participants can be arranged in a different way from that intuitively expected suggests that it is at least possible to conceive of different evolutionary courses. To dismiss this and assert that the cladogram in figure 3 must be right simply because it accords with native common sense, is not a scientific approach, because it allows only what we humans imagine is possible and denies us the opportunity of exploring all the alternatives and examining which one best fits the evidence at hand.



  1. What's the connection between the first and second citation?

  2. Nice sarcastic blog title.

    "Overwhelming evidence for evolution."

    What a laugh.