They’re among the most important fossils of all, mysterious monuments left by the very first organisms on Earth. Called stromatolites, some are smaller than a finger and others larger than a house. Among the most remarkable can be found in the Pilbara region of Western Australia, in the baking heat of what is jokingly called the North Pole Dome. There, white, red, and black rocks are dotted about in the grass. These stromatolites are thought to be little changed from when they first formed around communities of microbes an astonishing 3.43 billion years ago.
Some look like domes or upside-down ice cream cones. Others are small, conical shapes arranged a little like an egg carton. A few are crest-shaped, or even bear a passing resemblance to the ears of Mickey Mouse. Studies of their microbial descendants, known as cyanobacteria, suggest that these peculiar rocks slowly formed when mats of micro-organisms trapped sediments and precipitated carbonates. Because of their great and extraordinary old age, these stromatolites represent the first chapter in the rise of cooperation, a vestige of the ancient microbial communities that were among the first living things on Earth.
They are singular monuments. But as evolution shapes new kinds of cooperation, and cooperation heralds ever more inventive ways to construct an organism, novel ways to destroy and to defect also emerge. The stromatolites are a testament to cooperation among our ancient single-celled heritage, when they began to work together, and warn of the powerful and primitive forces that can be unleashed when that ancestry starts to reassert itself. I have come to think of these striking rocks as both milestones of the rise of living cooperation and as tomb-stones that warn of its potential fall.
Such single-celled creatures seem distant relations of modern life, yet in every sense, they are very much with us today. Their descendants are ubiquitous, clever, and unstoppable. They are able to eke out an existence in brutal conditions, from a subzero chill to the hell of scalding, acidic hot pools. They bask in the extreme saltiness of the Dead Sea and enjoy the caustic delights of soda lakes. They can be found in bone-dry deserts, such as Atacama. They thrive in the crushing depths of the ocean where temperatures are well in excess of 100 degrees Celsius. They lurk in the muds deep below the sea floor, along with toxic and radioactive sludges. Along the way, bacteria have invented all of biochemistry. And, at a stroke, they invented much of the machinery that turns in our bodies.
They also evolved ways to cooperate. Multicellular strings of bacteria were born around 3.5 billion years ago. Filamentous bacteria—so named because they form chains—kill themselves to yield precious nitrogen for the good of their sisters. Every tenth or so cell commits suicide for the benefit of this communal thread of bacterial life.
Another, quite different kind of microbial cooperation was revealed by the dogged efforts of Lynn Margulis at the University of Massachusetts, Amherst. She proposed that more complex “higher” cells were the result of symbiosis, when single-celled creatures became so closely associated that they worked as one. For example, around 1.8 billion years ago, there was an important moment when one kind of wriggling bacterium invaded another. Perhaps the former was seeking food. But this particular parasitic infestation suited both parties and evolved so that the participants formed a long, harmonious, and fruitful truce. This is what Margulis calls symbiogenesis and it led to the formation of higher cells, known as the Eukarya.
Thanks to this cooperation, a new, more complex kind of cell appeared on Earth. Whereas bacterial cells are relatively simple and known as prokaryotes, the newer cellular consortia, known as the eukaryotes, are the building blocks of plant and animal bodies, including our own. These cells contain organelles—which divide up the task of cellular life as organs do for a body—including a nucleus where their DNA resides. These organelles are the leftovers of earlier episodes of microbial mergers and acquisitions.
Peek inside your own cells and you will find these Russian doll coalitions. The most obvious example of symbiogenesis comes in the form of little lozenge-shaped structures called mitochondria. Not only do they look like bugs, they even have their own separate DNA that is passed down the maternal line, from mother to child. Our cells are driven by these descendants of bacteria that hundreds of millions of years ago traded chemical energy for a comfortable home. These organelles now power our muscles, our digestion, and our brains.
~~SuperCooperators: Altruism, Evolution, and Why We Need Each Other to Succeed -by- Martin A. Nowak
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