On Nov. 3, 1977, a new scientific revolution was heralded to the world — but it came cryptically, in slightly confused form. The front page of that day’s New York Times carried a headline: “Scientists Discover a Form of Life That Predates Higher Organisms.” A photograph showed a man named Carl R. Woese, a microbiologist at the University of Illinois in Urbana, with his feet up on his office desk. He was 50ish, with unruly hair, wearing a sport shirt and Adidas sneakers. Behind him was a blackboard, on which was scrawled a simple treelike figure in chalk. The article, by a veteran Times reporter named Richard D. Lyons, began:
Scientists studying the evolution of primitive organisms reported today the existence of a separate form of life that is hard to find in nature. They described it as a “third kingdom” of living material, composed of ancestral cells that abhor oxygen, digest carbon dioxide and produce methane.
This “separate form of life” would become known as the archaea, reflecting the impression that these organisms were primitive, primordial, especially old. They were single-celled creatures, simple in structure, with no cell nucleus. Through a microscope, they looked like bacteria, and they had been mistaken for bacteria by all earlier microbiologists. They lived in extreme environments, at least some of them — hot springs, salty lakes, sewage — and some had unusual metabolic habits, such as metabolizing without oxygen and, as the Times account said, producing methane.
But these archaea, these whatevers, were drastically unlike bacteria if you looked at their DNA, which is what (indirectly) Woese had done. They lacked certain bits that characterized all bacteria, and they contained other bits that shouldn’t have been present. They constituted a “third kingdom” of living creatures because they fit within neither of the existing two, the bacterial kingdom (bacteria) and the kingdom of everything else (eukarya), including animals and plants, amoebas and fungi, you and me.
Charles Darwin himself suggested (first in an early notebook, later in “On the Origin of Species”) that the history of life could be drawn as a tree — all creatures originating in a single trunk, then diverging into different lineages like major limbs, branches and twigs, with leaves of the canopy representing the multiplicity of living species. But if that simile was valid, then the prevailing tree of 1977, the orthodox image of life’s history, was wrong. It showed two major limbs arising from the trunk. According to what Woese had just announced to the world, it ought to show three.
Woese was a rebel researcher, obscure but ingenious, crotchety, driven. He had his Warholian 15 minutes of fame on the front page of The Times, and then disappeared back into his lab in Urbana, scarcely touched by popular limelight throughout the remaining 35 years of his career. But he is the most important biologist of the 20th century that you’ve never heard of. He asked profound questions that few other scientists had asked. He created a method — clumsy and dangerous, but effective — for answering those questions. And in the process, he effectively founded a new branch of science.
It began with a casual suggestion made to Woese by Francis Crick, the co-discoverer of DNA’s structure, who mentioned passingly in a scientific paper that certain long molecules in living creatures, because they are built of multiple small units, coded in sequences that change gradually over time, could serve as signatures of the relatedness between one form of life and another. The more similar the sequence, the closer the relative. In other words, comparing such molecules could reveal phylogeny. The new branch of science is called molecular phylogenetics. Wrinkle your nose at that fancy phrase, if you will, and I’ll wrinkle with you, but in fact what it means is fairly simple: reading the ancient history of life from the different sequences built into such molecules. The molecules mainly in question were DNA, RNA and a few select proteins. Carried far beyond Woese and his lab, these efforts have brought unexpected and unimaginable discoveries, fundamentally reshaping what we think we know about life’s history, the process of evolution and the functional parts of living beings, including ourselves.
Woese vanished into his lab, but his insights and methods, and his successors in applying them, have produced in particular one cardinal revelation: The tree of life is not a tree. That old metaphor is obsolete. Life’s history has been far more tangled. [Continue reading…]