The one in trillions and trillions origin of complex life on earth

I’m reading, I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong.  Really good stuff.  Early in the book I was intrigued by a footnote to Yong’s own earlier article on the hypothesized union of archaea and bacteria to create complex cellular life.  I went and found the Nautilus article.  Utterly fascinating.  Almost as amazing as the still unexplained origin of life on earth is the origin of complex life on earth.  The simple prokaryotes of bacteria and archaea coming together to create a complex eukaryotic cell appears to have been a one in trillions chance that only happened once in the history of the planet.  Mind-blowing.  You should totally read this.  That said, highlights:

The alternative—let’s call it the “sudden-origin” camp—is very different. It dispenses with slow, Darwinian progress and says that eukaryotes were born through the abrupt and dramatic union of two prokaryotes. One was a bacterium. The other was part of the other great lineage of prokaryotes: the archaea. (More about them later.) These two microbes look superficially alike, but they are as different in their biochemistry as PCs and Macs are in their operating systems. By merging, they created, in effect, the starting point for the first eukaryotes.

Bill Martin and Miklós Müller put forward one of the earliest versions of this idea in 1998. They called it the hydrogen hypothesis. It involved an ancient archaeon that, like many modern members, drew energy by bonding hydrogen and carbon dioxide to make methane. It partnered with a bacterium that produced hydrogen and carbon dioxide, which the archaeon could then use. Over time, they became inseparable, and the bacterium became a mitochondrion.

There are many variants of this hypothesis, which differ in the reasons for the merger and the exact identities of the archaeon and the bacterium that were involved. But they are all united by one critical feature setting them apart from the gradual-origin ideas: They all say that the host cell was still a bona fide prokaryote. It was an archaeon, through and through. It had not started to grow in size. It did not have a nucleus. It was not on the path to becoming a eukaryote; it set off down that path because it merged with a bacterium. As Martin puts it, “The inventions came later.”

This distinction could not be more important. According to the sudden-origin ideas, mitochondria were not just one of many innovations for the early eukaryotes. “The acquisition of mitochondria was the origin of eukaryotes,” says Lane. “They were one and the same event.” If that is right, the rise of the eukaryotes was a fundamentally different sort of evolutionary transition than the gradual changes that led to the eye, or photosynthesis, or the move from sea to land. It was a fluke event of incredible improbability—one that, as far as we know, only happened after a billion years of life on Earth and has not been repeated in the 2 billion years since. “It’s a fun and thrilling possibility,” says Lane. “It may not be true, but it’s beautiful.” [emphasis mine]

Lots more good stuff.  If you have any small interest in science and or biology (or just the origins of complex life), read it.


About Steve Greene
Professor of Political Science at NC State

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