Jerry Coyne Notwithstanding, as an "Explanation" for the Rise of Complex Animal Life, Oxygen Is Now Eliminated from the Running
The other day at Why Evolution Is True, Jerry Coyne was busy giving another lame cartoonish dismissal of the argument in Darwin's Doubt. This was in reference to an article at Big Think by Kas Thomas, "The Trouble with Darwin."
Thomas is up on some of the modern impediments to regarding Darwinian theory as anything other than a deeply unsatisfying idea about biological origins. Thomas:
[Evolutionary theory] doesn't explain the Cambrian Explosion, for example, or the sudden appearance of intelligence in hominids, or the rapid recovery (and net expansion) of the biosphere in the wake of at least five super-massive extinction events in the most recent 15% of Earth's existence.
The mention of the Cambrian explosion, of course, comes straight from Stephen Meyer's new Intelligent Design book saying that because we don't understand how many major body plans originated so rapidly (by "rapidly," we're talking 20 million years), Jesus must have done it. But our lack of understanding is due not to a paucity of theories, but to a surfeit of theories (oxygen, predators, gene regulation, and so on), and our present inability to distinguish among them.
This is not much of an improvement over Coyne's previous absurd précis of Darwin's Doubt, ""Yes, baby Jesus made the phyla!" It's a book that evidently he still hasn't read anything serious about much less read the thing itself. Well, one of his "surfeit of theories" gets shot down in an article in PNAS that just came across my desk: "Oxygen requirements of the earliest animals."
There's nothing about lower oxygen levels that would forbid the rise of early animals, thus nothing about higher levels that should be considered illuminative of the enigma of animal life:
A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth's surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850-542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635-542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5-4.0% present atmospheric levels. Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period. Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans. Instead, other ecological and developmental processes are needed to adequately explain the origin and earliest evolution of animal life on Earth.
More about the importance of the finding:
The relationship between the origin of animals and the oxygen content of the atmosphere is a pressing issue in historical geology. Here we challenge the widely held view that low levels of atmospheric oxygen delayed the origin of animals up until 850-542 million years ago. We provide experimental evidence suggesting that the last common ancestor of animals could have thrived in oxygen levels as low as 0.5% to 4% of present atmospheric levels, which were likely met on Earth well before animals evolved. This was achieved by observing the survival of sponges, basal animals similar to the earliest metazoans, under low-oxygen conditions in the laboratory. These results encourage us to reconsider the environmental constraints on the origin of animal life.
An infusion of oxygen wouldn't do it. But you'd know that from ENV's post back in August, "Cambrian Animals? Just Add Oxygen," which cast a peery eye on the hypothesis that this was ever a remotely plausible way to explain an eruption of biological information, observing that "We're not sure if this one passes the laugh test." Anyway from among Coyne's "surfeit," that's one that is knocked down with ease. Next?
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Image credit: Fabio Marini/Flickr.