Cambrian explosion:
Early in the study of fossils apparently somebody picked up a rock near Cambridge and found fossils in it. That sounds reasonable, but I will not swear to it. At all events, there is an assemblage of fossil forms designated Cambrian, and they are among the earliest fossils known. Certainly they are the earliest fossils of complex life that can be found in great numbers.
Earlier rocks are almost bare of the fossils of complex life. There are a few tiny areas known with Precambrian fossils. The appearance of the Cambrian fossils has been called the, “Cambrian explosion.” Life exploded onto the scene.
It seems almost biblical. And anything that sounds biblical that appears in science I am immediately suspicious of. But the fossil record is far too robust to suggest that some sort of prejudice has been altering the interpretations by our scientific friends. The sudden emergence of so many forms was real.
Quite early on in this project I was casting about for numbers. I wanted to know how many generations it took for a species to develop. That had implications obvious to me for how large a population would be stable in the long run. This was years before epigenetic phenomena were described, so I was stuck with thinking about genes and nothing else.
The classical divisions of life were into kingdom, phylum, class, order, family, genus and species. I guessed that it would take a certain number, more or less, of generations for a population that had been separated into two to develop into different species. I then, and this was the wildest guess, supposed that it would take a family a certain number of speciation times to break into two genera, the same number of genera times to split an order into families and reasoning backwards thusly got to a time it took for some pre-cursor to branch into two kingdoms. Then from some date in the past, one comes back down and decides on speciation time.
The unknowns in this far outweighed the knowns. One had to suppose that somehow the paleontologists had devised their scheme so that the “distance,” whatever that meant, from phylum to class was the same as the distance from genus to species. But I had a burning question and racked my brain until I came up with a number. Fortunately I have forgotten it. I am sure I would be embarrassed. My current thinking is two thousand generations to speciation and maybe as many as four based on mice in the Canary Islands, rabbits in the Azores and Camels.
But there was always a sword hanging over the whole line of reasoning. Back in the third grade Mrs. Thompson was not supposed to teach us evolution. She made up for that by leaving in the classroom a little booklet that showed the fossil record with an artist’s depiction of what various life forms might have looked like at different times. It did not take a child long to figure out that evolution had been going on. There are really two definitions of evolution I know of. One is the Aristotelian idea, which can be summarized. Things happen by chance; what works is what persists. Then there is the Darwinian idea, which can be summarized, an organism that is more fit is likely to have more offspring than a less fit organism, and this numerical advantage will fix the inheritable component of the fitness in that population, and as the changes accumulated the species will change into a new species, which is a matter of happenstance as hybrid infertility never did any species any good.
The Darwinian model is the currently accepted one. It has its strengths and its weaknesses, such as the one I have mentioned: there is an island with rabbits which eat only grass and foxes that eat only rabbits. One day a mutation occurs that lets the fox catch any rabbit on the island. Soon lots of foxes have it. Then all the foxes that lack it die. Then all the rabbits die. Then all the rest of the foxes die. That is no problem for the Aristotelian idea; it didn’t work. In terms of fitness, you will have to do handsprings to explain how the mutation made each fox less fit.
At all events, Aristotelian evolution was obvious from the booklet, and I was surprised when people spoke of evolution as if it was an intellectual triumph.
The thing is that already in the Cambrian era demonstrated there were different life forms, phyla, although I did not know the word at the time. The artists, a good Darwinian, had done his best. He drew the earlier life forms as small and maybe just a little oversimplified. But he could not honestly hush up the Cambrian explosion altogether.
This was of no consequence until I was trying to work out speciation time. Then it became obvious to me that life was older than the fossil record, a lot older. I thought maybe twice as old.
That is now somewhat less heretical. The issue has been studied, (Douglas H. Erwin et al. The Cambrian Conundrum: Early Divergence and Later Ecological Success in the Early History of Animals SCIENCE vol. 334 no. 6059 November 25, 2011 page 1091) and using a number of approaches they push back the origin a little over 200 million years. I would have said it went back a lot longer than that.
The key issue here is that in order to have all these life forms, one must have speciation in earnest. And speciation cannot exist in a very large randomly mating population. Because of the way chromosomes move about, speciation effects would exterminate the population. So there had to be ways of limiting population sizes.
And this had to be backed up with iron discipline. In other words the epigenetic mediated infertility that I have been pursuing is not just some recent annoyance. It has to go back past the earliest fossils to some time far beyond our ken.
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