I’ve been reading THE VITAL QUESTION by Nick Lane, New York, W. W. Norton, 2015. In this book author Nick Lane, biochemist at University College, London, defines in exacting logic where life may have begun on Earth, why archaea and bacteria got stuck “… at the bacterial level of complexity for more than two billion years,” and why the jump to complex eukaryotic life, to critters like us, was made possible by difficult, perhaps unique, endosymbiosis events—the engulfing of one microbe by another.
All this is of interest in our search for exolife. If we understood how life began on Earth, we would know better how to look for life elsewhere. The author goes into great detail describing the alkaline hydrothermal vents on Earth’s ocean floor. They most likely provided the ideal environment for harnessing the proton exchange required to get simple life started here. We would do well to learn more about those vents before we study possible life-starting environments on Europa, Titan, and Enceladus.
Lane points out that some earlier speculation about life’s beginning on Earth was based on misunderstanding of its ancient atmosphere. Recent studies with zircon suggest that the early atmosphere was dominated by oxidised gases emanating from volcanoes, notably carbon dioxide, water vapor, nitrogen gas and sulphur dioxide…It was not rich in gases conducive to organic chemistry—hydrogen, methane and ammonia.”
He points out that RNA is far too complex a molecule to start with. He stresses the need to consider the energy requirements of cellular and genomic activity. He describes in detail the alkaline hydrothermal vents and how they could provide the gentle environment to get simple prokaryotic life (the archaea and bacteria) started.Lane argues that all of us, every form of life on Earth except the archaea and bacteria, have complex cells called eukaryotes that include …essentially the same cellular machinery—”…a nucleus [with DNA]..a .nucleolus…histone proteins, chromosomes, capped with ‘telomeres’…’genes in pieces’…interspersed by…introns….Golgi apparatus, cytoskeleton, a nucleus, motor proteins, mitosis and meiosis…” He notes that “almost all the genes involved (those encoding…’signature proteins’) are not found in prokaryotes [the cells of bacteria and archaea.].”
As a result of endosymbiosis between simple organisms on a 2-billion-year-old Earth, cells that became complex eukaryotes now include the biomachinery listed above, plus endosymbionts: mitochondria or (later) chloroplasts (to make plants). Lane says, “…the singular origin of complex life might have depended on their acquisition…” because this endosymbiosis provided energy efficiency. He explores in detail the bioenergetics that allowed our eukaryotic cells to conserve energy.
At the same time, free unused symbiotic mitochondrial genes must have looked around their host cell for something more useful or interesting to do. Hence many of them experimented with light and many of us learned to see. We learned to utilize different kinds of food. Plant endosymbionts with chloroplasts took the extra genes and learned to use carbon dioxide to make leaves and bark. Eventually, some of us grew legs, arms and brains.
The author does a masterful job of introducing and exploring critical questions. Why did the bacteria never evolve into more complex critters? Perhaps they stayed stuck due to a “constrained structure” that limited their ability to capture energy. That was the trick the mitochondrial symbionts provided. The resulting eukaryotes learned that “…proton gradients were central to the emergence of cells…”
Lane poses other questions about complex life. Is it really so rare—even here on Earth? Apparently, the energy provided by mitochondria, once engulfed by ancient archaea and appropriated to become part of eukaryotic cells, only happened once in 4.5 billion years on Earth. He shows how this endosymbiosis provided us eukaryotes with a huge energy advantage, leaving the bacteria and archaea to proliferate and fill the Earth with ongoing success, unchanged. There are no missing links between them and us. That’s why Lane emphasizes the importance of this singular event.
Lane enforces this view by noting that genome sequences of ancient protists like Giardia show that they are not missing links; they had lost their mitochondria by “reductive evolution.” Thus, “eukaryotes are monophyletic…plants, animals, algae, fungi and protists all share a common ancestor.” It’s the reason that all complex life on Earth contains the same biomachinery.
The uniqueness of complex life in the universe was suggested in Ward and Brownlee’s RARE EARTH. They give us many geologic and astronomic reasons why Earth lucked out in the effort to produce complex life. Now we have Lane’s bioenergetic arguments to add to our luck.In Lane’s words: “…a synthesis of energy and evolution could be the basis for a more predictive biology…wherever it might exist in the universe.” In any case, his analysis of how Earth’s life might have started in alkaline hydrothermal vents is a dandy model for our exobiology searches. More on this tree-of-life-changing book next month.
Author of The Archives of Varok
The View Beyond Earth (Book 1.)
The Webs of Varok (Book 2.)
Nautilus Silver Award 2013 YA
ForeWord IBPA finalist 2012 adult SF
The Alien Effect (Book 3.)
An Alien’s Quest (Book 4. coming in 2016)
Excerpts, Synopses, Reviews, On Writing, Characters and More-