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This definition from Wikipedia will suffice: The Cambrian explosion, or less commonly Cambrian radiation, was the relatively short evolutionary event, beginning around 542 million years ago in the Cambrian Period, during which most major animal phyla appeared, as indicated by the fossil record.
What caused this sudden emergence of complex animals, the origin of the first Bilaterians?
To begin, I will put that question in a form that will lead to what I think is the correct answer: How did certain gene pools suddenly acquire the ability to produce with great precision complex animals?
No one has ever observed a gene pool but I find that concept—all the genes for a particular lineage comprising a single evolving entity—of great usefulness in resolving problems of deep evolution. The meager fossil record cannot tell us much about events that occurred more than 500 million years ago but simple logic, probabilistic thinking and the gene pool concept tells us this: complex animals did suddenly come to exist and their construction was controlled by their respective gene pools.
Although others look (wrongly, I think) for explanations of the Cambrian Explosion in environmental changes I believe the correct answer can be reached if we focus exclusively on this question: What evolutionarily significant events could have changed the composition of those gene pools?
My explanation.
1. In forming every multicell, or, to use Dawkins’ Selfish Gene terminology, every survival machine, the gene pool(s) of Ur-Bilaterians were obliged by prior events to place in each somatic cell a cancer-triggering mechanism, i.e., functioning oncogenes. (See Note.)
2. Lethal juvenile cancer was initiated following or concurrent with the occurrence of errors in somatic replication during development. (All mutagens are carcinogens; all carcinogens are mutagens.)
3. Selection pressure created by lethal juvenile cancer favored the survival of perfectly-formed animals, those that followed strictly a program of precise formation of individual somatic cells, thus avoiding juvenile death from cancer. In other words, cancer selection directed the evolution of Bilaterians towards increasingly efficient construction of juveniles’ somatic cells, efficiency that enabled greater complexity and greater diversity. (See the One-Eyed Thinking section here.)
4. Operating under a cancer-enforced imperative of precise development, the Bilaterian gene pools acquired masterful control over construction of the entire individual animal. Innovative proposals emanating from favorable genetic mutations would be faultlessly expressed.
5. Without the existence of functioning oncogenes and without the actual occurrence of innumerable juvenile cancer deaths no gene pool in control of constructing multi-celled survival machines would have produced complex animals; without an imperative of hyper-precision they would have survived as producers of cell colonies.
Alternative explanations.
No theorist could seriously disagree with my conclusion—it is a tautological certainty—that the earliest Bilaterian gene pools, descendants from producers of mere cell colonies, somehow acquired the ability to produce complex animals.
To my knowledge no one has proposed any other evolutionarily-effective mechanism (one observable in extant animals) that could have changed the composition of the gene pools in a way that accounts for the sudden prodigious production of complex animals. Biology’s theorists seem silent on the matter.
Perhaps it is appropriate to again suggest that their implicit solution is “insert miracle.”
Note.
My theory of the evolutionary history of Bilaterians begins with the embedment of functioning oncogenes in all somatic cells. As to the origin of those instruments of death, I offer a reasoned explanation for their possible origin in Cancer Selection but, because the validity of my theory does not in any way depend on the legitimacy of that unavoidably speculative explanation, I placed it in an appendix.
Comments and questions are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
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