A news article at Nature, "Oxygen fluctuations stalled life on Earth," is remarkable for skirting the main issue, the primary enigma, in the geologically sudden rise of complex animal life. Certainly, animals need oxygen and the article is at pains to show how oxygen levels on the early Earth were "dynamic" rather than stable, sometimes leaving the planet starved of the vital gas.

Oxygen concentration spiked once about 2.3 billion years ago, then again at 800 million years ago, well before the Cambrian explosion about 530 million years ago. The "boring billion" refers to the period during which not much happened in the history of life, when Nature says evolutionary progress was "stalled."

What does this mean, though? Does a car "stall" for want of gasoline if, besides gas, it’s also missing an engine, wheels, steering system, etc., the integrated and designed systems that make a car a car?

Reporter Jane Qiu quotes geobiologist Malcolm Walter who cautions:

Atmospheric oxygen levels were "a key environmental constraint on animal evolution".

Walter stresses, however, that genetic innovations are also crucial for the evolution and diversification of complex life. The evolutionary engine did not truly rev up for another 260 million years after the second oxygenation event, when the Cambrian Explosion gave rise to modern animal phyla in just 20 million years — a geological blink of the eye.

"Until the environment was right, and until genetics tools were there, [the evolution of complex life] couldn’t have happened," says Walter.

The right environment is obviously a necessary condition, but far from the toughest to explain. In accounting for what happened in that "geological blink of the eye," the genetic side of things is surely the heart of the puzzle, as Stephen Meyer writes in Darwin’s Doubt. Ms. Qiu admits:

Others suspect the prolonged hiatus in evolution may be down to it taking a long time to develop the necessary genetic machinery.

You don’t say. And how did that "develop," exactly? She doesn’t say.