How many evolutionary explanations for the Cambrian explosion have come and gone so far? We’ve seen the oxygen theory, the cancer theory, the slime theory, and others. Here’s another contender reported by Quanta Magazine: the tipping-point theory. Animals were trying really hard to hit on regulatory gene networks by chance. It took a really long time, but — finally! — they hit the lottery, and it all took off.
This model is the brainchild of Nicholas Butterfield of the University of Cambridge. He published it in Geobiology. It’s open access, so you can take a look. Back at Quanta, staff writer Jordana Cepelewicz says that the new theory not only explains the suddenness of the Cambrian explosion, but why it took so long.
Approximately 540 million years ago, life rapidly diversified in an evolutionary burst — a biological “Big Bang” that witnessed the emergence of nearly every modern animal group. Scientists have long sought to determine what caused the Cambrian explosion, and to explain why animal life didn’t take this step at any point about a billion years earlier. [Emphasis added.]
Butterfield doesn’t buy the oxygen theory. He points to other situations where animals make do without modern levels of oxygen. Surely microbes could have figured out how to get the needed energy. Besides, there should have been enough oxygen in the oceans to support life long before the so-called Great Oxidation Event 2.4 billion years ago — and that was long before the Cambrian explosion (540 million years ago).
Before animals could explode onto the scene, he thinks, they needed two things: the ability to re-engineer oxygen structure in the oceans (what he calls “aquatic bioturbation”) and the invention of gene regulatory networks to adapt to the new environment.
Eventually, this cascading interplay between animals’ inadvertent re-engineering of ocean structureand their adaptive responses to those changes reached a tipping point. “The system went critical,” in Butterfield’s words, resulting in the sudden eruption of animal diversity and complexity during the Cambrian.
The delayed appearance of animals in the ocean was therefore not caused by a lack of oxygen, according to Butterfield, but rather because blind Darwinian evolution needed time to arrive at that tipping point. “The gene regulatory network to build an animal is the most complex algorithm that evolution has ever produced,” he said. “And it’s only ever happened once, [just as] it’s only ever happened once in land plants,” which he points out are the only other lineage of organisms to have derived differentiated tissues, organs and organ systems. “And that took even longer. It followed the evolution of animals by another 100 million years.”
Notice first of all that Butterfield turns the oxygen theory on its head. A rise in oxygen was a result, not a cause, of the explosion. Secondly, observe that his argument is basically a blind watchmaker argument: “blind Darwinian evolution” was trying very hard to arrive at the magic combination to unlock the inherent potential of animals to evolve. It took a long time, but once it happened, the rest was easy. Selective pressures would guarantee the emergence of muscles, eyes, digestive systems, armor, and all the rest.
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Source: Evolution News