Carl R. Woese, o cientista que mexeu profundamente na árvore da vida de Darwin e no entendimento da origem e evolução da vida

terça-feira, agosto 14, 2018

The Scientist Who Scrambled Darwin’s Tree of Life

How the microbiologist Carl Woese fundamentally changed the way we think about evolution and the origins of life.

By David Quammen

Source/Fonte: Science

Aug. 13, 2018

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.


Read more here: The New York Times