Fossil record:
When scientists get to talking about evolution, there are some problems. For one thing, there is incoming flack from people whose primary interest apparently is not science. Another problem is that there is no object in the bureau of weights and measures that specifies exactly what one unit of evolution is. I cannot even think of such a word. In the absence of a unit, evolution is hard to count. In the absence of a count, it is hard to define a speed. Undeterred, scientists debate the question of how fast evolution proceeds.
It was trendy recently for people to debate whether evolution proceeds always at the same pace. The intuitive answer is that, so far as a pace can be imagined, evolution is sometimes faster and sometimes slower. Anything else would involve some sort of governor that would raise any number of imponderable paradoxes.
But scientists dislike intuition with good reason. Evidence is preferred. And on the basis of evidence two schools developed. One school held that evolution always proceeded with slow, majestic tread because the only raw material was mutated genes which evolution could select among, and the number of such mutations in any species in any generation was probably high and constant. To these, evolution crept along, and the fans were called Creeps.
Taking the other extreme some scientists looked at the fossil record. I have made no direct study, but from what I read, the fossil record does not creep. A species may turn up in the fossil record and last for a very long time unchanged. Then unless it comes down to the present, the species vanishes from the fossil record never to return. It does not morph imperceptibly into another, it just dies out. Mean while, while some species are dying, others are appearing. They don’t emerge imperceptibly from an older species, they just pop up. Evolution so far as fossils go proceeds by jerks. And accordingly the fans are called Jerks.
Things are somewhat less troubling when it comes to groups of species. We here scientists refer to such things as “an early form of bird” without their voices trembling. The do not speak so of any “early form of chicken.” Either it was a chicken or it was not. So I shall beg the question of evolution in groups of species, be they genera or families and so forth and just talk about species. Why do they seem to exist against a background of “punctuated equilibrium,” as it is more properly called. Why do species appear with such abruptness that intermediate forms are not recognized, and having appeared, why is their form so-to-speak “fossilized?”
If you have been following along the arguments in the web site, the answer must be obvious. Evolution proceeds until the organism has accumulated so many good genes (using the term broadly and roughly) that no more can be carried. They could only be maintained by eliminating the mutations that would degrade them by eliminating offspring that carried the bad mutations. In the absence of any scope for more complexity, evolution is paralyzed.
Thus you can spend your life looking. The Grand Canyon is some 70 miles long and mile deep. Counting both walls and given the walls are not perfectly straight, that is some 150 square miles of fossils. Mostly it is the age of trilobites. The dinosaurs are not there. That level was above what is now ground level and has long since eroded away. But in those 150 square miles, if you can find one species changing imperceptibly into another, you will become very famous. The absence of such a discovery amounts to a lot of evidence for one of our assumptions, that evolution has proceeded as far as it can go.
And there is another line of evidence from the same fossil record. Because a very large population cannot maintain as many genes against mutation pressure as a normal sized population, animals must exist in small mostly isolated populations. A bigger population can produce more mutations than a smaller one, but that mutation must occur in one of those small isolated populations in which animals actually live. It would require inconceivable luck for the transition forms even to become part of the fossil record at all, much less be discovered and understood.
So evolution sits very still or creeps literally imperceptibly awaiting a lucky moment when the need for some of the genetic heritage of a species becomes redundant – a new food source or absence of a key predator or whatever – and then it jerks off to a new equilibrium. It probably does not actually need to wait for those advantageous mutations. There is probably a cloud of nifty new gene forms around most species, each advantageous enough to stay longer than chance would predict it to stay in the gene pool, but not strong enough to become established until opportunity arises. Then things happen fast.
The fact that things must be so is further evidence for the fact that there is a genetic limit to population size.
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