The Fossil Record
Absence of Intermediate Forms
One objection to the theory of evolution is that there isn't a complete succession of of intermediate types found in the fossil record, but instead just lots of one sort of plant or animal, and then, bang, lots of another quite different sort.
Now, the way Darwin saw it, the process of evolution proceeded slowly and gradually. New and fitter variants appeared and gradually eased out their less fit precursors, in an almost immeasurably slow process. And, given this view, one would indeed expect to see a succession of types, each slightly variant from each other, in the geological column.
The standard model of evolution is one of gradual, steady succession. Over some long period of time, some ancestor of a giraffe gradually evolves into a giraffe.
The standard model assumes that populations stay relatively constant, at the "carrying capacity" of their environment. As transitional intermediates appear, they gradually replace their forebears, and are in turn replaced by more advanced transitional types. And the fossil record would show this steady process of transition.
Behind this notion of gradual evolution is an equilibrium, "steady-state" model of life, in which nothing dramatic ever happens. There are no mass extinctions. There are no catastrophes. There are no population explosions. Or, if there are, they are unusual events which interrupt the normal process of gradual evolution. Such equilibrium models are mathematically convenient and easy to understand.
Fast Evolution during Population Explosions
Idle Theory takes the view that life isn't in equilibrium, but is a dynamic process that is constantly changing. The "carrying capacity" of some environment is a fiction that comes from an equilibrium vision. Idle Theory's dynamic computer simulation models 1 are oscillating systems, with plant and animal population booms and crashes. Dynamic systems are mathematically complex and difficult to understand.
A dynamic model offers a possible explanation for the absence of intermediates in the fossil record. It is that, rather than evolution happening at a steady rate over the long ages of life, most evolution actually takes place during periods of time which are almost instantaneous in geological terms - population explosions.
If it is taken that, in any reproducing population, only a small fraction of offspring vary from their parent, it follows that it will be in the largest populations that the greatest numbers and types of variants will appear. And the largest populations are found during population explosions. So the greatest number of variants will appear during population explosions.
Population explosions can't be sustained for long, however. A population explosion is followed by a population crash. A rising population of grazing animals must, sooner or later, consume most of the vegetation on which they feed, and in the resulting starvation, most must die. The small population of survivors then slowly grows in numbers until there's a new population explosion, with lots of new variants appearing, followed by a population crash. And so on, again and again.
At the climax of a population explosion, the population will be composed almost entirely of large numbers of the ancestral types extant prior to the explosion, because it is these types which have been gradually increasing in numbers since the previous crash. In addition there will be a relatively small populations of variants, and an even smaller number of variants of those variants, and so on to tiny populations of variants which are removed by 10 or 20 or more steps from the ancestral types.
Now, if it happens that the ancestral types, regardless of their high numbers, are entirely extinguished during the population crash, and it is some of the variants 10 or 20 steps removed from the ancestral types that survive the population crash, then the geological record should show the extinction of the ancestral type, and its replacement by a quite different type, many steps removed from the extinct ancestor, with the intermediates represented for a comparatively brief period during the population explosion. Most of these variants will appear at about the same time. Instead of variants evolving gradually in steady succession, they will be bunched together during the population explosion.
If so, the fossil record should show a long periods during which only the giraffe ancestor is found in the fossil record in small numbers, and then a short period during the population explosion where they are extremely abundant and accompanied by small numbers of numerous variants, and then, after the population crash, a long period in which small numbers of one or two of the variants are found.
The Fossil Record
But this assumes that every creature is fossilized after death. If one assumes that not all creatures that die become fossilized, but instead their remains are either entirely destroyed by scavengers, or eroded by wind, water, and chemical decomposition, it will only be a few which chance to be immediately preserved after death which will found in the geologic column. If so, then while the large ancestral populations will leave the most fossils prior to the population explosion, and the survivors of the subsequent population crash will also appear in the fossil record, the short-lived intermediates, which appeared during the brief population explosion, and became extinct in the subsequent crash, will leave the fewest fossils. They simply existed in too few numbers, and for too short a time.
In addition, even if small numbers of intermediates exist in the fossil record, the chances of palaeontologists actually finding them are equally small.
The result will be that the fossil record will show large numbers of one type of creature, and then large numbers of a quite different type - and next to no intermediates. Instead of a steady succession of intermediates in the fossil record, there will be one type followed by another type several stages removed.
Since the highest populations occur during the population explosion, it should be at this point in the geologic column - the sequence of deposition layers with the most recent at the top - that there will be the maximum numbers of fossils. In between, there will be relatively few fossils. That is, fossils should generally appear in distinct beds. As you go chipping through the geologic column, you should find that in some layers there are few fossils (because there were few survivors after a population crash), and then there are layers with many fossils (corresponding to population explosions), followed by layers with few fossils.
And that was what I thought I saw in the ammonite Jurassic deposits at Lyme Regis in Dorset, England. As I recollect it, as I prised open the layers, mostly I'd find nothing. And then I'd open up a layer in which there were dozens of small ammonite impressions. I remember being vaguely puzzled why the ammonites didn't seem to be evenly distributed in the depostion layers.
One sunny day I'm going to head out along the beach west of Lyme Regis again, past the sunbathers, over that limestone plateau with the three foot wide ammonites coiled in the rock underfoot, over the barnacled rock field, and onwards along the pebbles beneath the cliff - until I get to where the beach bends right, that special place where the cliff falls in blocks of splintered grey shale, and all you need is a table knife or a screwdriver to prise the damp layers apart to find the faint fossil impressions inside. And what I'll do is take some block, and lift off one thin tile after another of shale, and count whatever fossils I find underneath, until I've gone right through the whole block. It'll be a test of this theory. Because if I'm right, I'll find that mostly there aren't any fossil impressions in most layers, and lots in others.
(How will I know which is the top of the block? How thin do I slice the tiles? How thin can I slice the tiles?)
Postscript 2010: And yes, I did make it back to Lyme Regis, and walked westward along the beach to the place where I’d found the soft shales I’d prised apart with a screwdriver years before. At that place (and in fact all along the coast) the cliffs are gradually being eroded into the sea, and every time you go there it’s different. And when I returned, there were far fewer blocks of shale to break open, and in the ones that I split open I found … almost nothing at all!
Author: Chris Davis
First created: 19 Sep 2003
Last updated: Nov 2010