How the Cambrian explosion might have happened

The ‘Cambrian explosion’ is the name given to the geologically short time period of about 20 million years that occurred around 500 million years ago in which there seemed to be a surge of new kinds of organisms that appeared in the fossil record. Critics of evolutionary theory, always on the look out for what they see as possible signs of divine intervention, seized on it as something that seemed unlikely to have happened due to the slow processes of natural selection and thus a signal that god may have intervened to speed things up a bit.

I have never quite understood the appeal of models of god’s actions that require him to act in ways that are so subtle as to be so hard to detect. But religious people have no option since they realize that dramatic things like parting the sea are non-starters in this modern day and age. Looking for tiny signals in the vast amount of noise is the best option they have.

But a report on a new study suggests that while the rate of evolution during that period must have been about five times the current rate, that is not unusually fast and that the rate of evolution can speed up considerably when organisms find a new niche that allows for new opportunities to expand, as likely occurred in the Cambrian period.

Lee explains that those faster evolutionary rates are likely explained by game-changing innovations—predation, vision, and active swimming, for instance—that opened up a range of new possibilities for arthropods during the Cambrian. That kind of evolutionary fast-forward has also occurred when animals colonize new environments, he says. Think birds or mammals on islands, or snakes in the sea.

“When a lineage acquires a novel adaptation, they often undergo a burst of evolution, to fill up a newly opened range of environments and niches,” Lee says.


  1. bad Jim says

    Typical atheist rationalization. Is it so hard to understand that God had an inordinate fondness for trilobites?

    (The natural history museum in Prague has a stupefyingly large collection. The mineral shop in my town had a beautifully detailed specimen, at least 15 cm long, for only $5,000. I was deterred less by the price than the thought that it belonged in a museum; besides, I already have two little ones.)

  2. Nick Gotts says

    I think the bigger puzzle is why the Cambrian explosion took so long to happen. Eukaryotes probably arose (by symbiosis) around 1.5 or 2 billion years ago, and judging by the number of times it occurred, eukaryote multicellularity was not particularly difficult to achieve – so why the long wait?

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