Vital Question: Energy, Evolution, and the Origins of Complex Life

by Nick Lane

And so we draw to a close. While bioenergetics do not predict from first principles that there should be fundamental differences between bacteria and archaea, these considerations do explain how and why they could have arisen in the first place. The deep differences between the prokaryotic domains had nothing to do with adaptation to extreme environments, such as high temperatures, but rather the divergence of cells with membranes that were obliged to remain leaky for bioenergetic reasons. While the divergence of archaea and bacteria might not be predictable from first principles, the fact that both groups are chemiosmotic (depending on proton gradients across membranes) does follow from the physical principles discussed in these last two chapters. The environment most realistically capable of giving rise to life, whether here or anywhere else in the universe, is alkaline hydrothermal vents. Such vents constrain cells to make use of natural proton gradients, and ultimately to generate their own. In this context it’s no mystery that all cells here on earth should be chemiosmotic. I would expect that cells across the universe will be chemiosmotic too. And that means they will face exactly the same problems that life on earth does. In the next part, we’ll see why this universal requirement for proton power predicts that complex life will be rare in the universe.