Cobra Effect · Microbes and the machinery of life
The third branch of life
How comparing one molecule revealed a whole domain of life hiding in plain sight.
7 cards, read aloud in 2:36, with a test and sources.
In the 1970s, living things were divided into two great groups.
Bacteria were simple cells without a nucleus. Everything else, from yeast to trees to people, had cells with a nucleus. Carl Woese, at the University of Illinois, wanted to trace how all living things are related.
Woese studied a molecule found in every living cell.
Ribosomes, the machines that build proteins, contain a kind of RNA that changes very slowly over evolution. By cutting it into pieces and comparing the fragments, he could measure how closely organisms were related. The work was painstaking, with patterns of spots read one by one from photographic film.
In 1977, some microbes that make methane did not fit.
Working with George Fox, Woese found that their RNA was as different from bacteria as from anything else. Under a microscope, they looked just like bacteria. But in their molecules, they were a separate line of life.
Woese and Fox proposed three primary kingdoms of life, not two.
The newly recognised group was first called archaebacteria. The news reached the front page of The New York Times. Many biologists were sceptical, and some dismissed the idea outright.
In 1990, Woese and his colleagues named three domains of life.
They called them Bacteria, Archaea and Eucarya, the last being living things whose cells have a nucleus. Archaea, they stressed, are not bacteria at all. Acceptance came slowly, and some prominent biologists were still objecting in the late 1990s.
Archaea turned out to be almost everywhere.
Many live in hot springs and very salty lakes, but they are also common in oceans, soils and the human gut. Some researchers now think that the cells of plants and animals arose from within the archaea. Carl Woese died in 2012.
So when things look alike, ask what a deeper comparison might show.
Under a microscope, archaea and bacteria look much the same. Only a comparison of their molecules showed how different they are. Appearances can hide some of the deepest divisions of all.
Sources
- Carl Woese, Linda Hall Library. His life and the discovery of the archaea.
- Phylogenetic structure of the prokaryotic domain: the primary kingdoms, Woese and Fox, PNAS, 1977. The paper that proposed a third kind of life.
- Archaea, Wikipedia. What archaea are, and where they live.
Nearby ideas
- The cells that took in bacteria. How a rejected idea showed that parts of our cells were once free living bacteria.
- The little animals in a drop of water. How a Dutch cloth merchant with homemade lenses discovered a hidden world of life.
- The infection with no genes. How a brain disease in sheep led to infectious proteins with no genes at all.
- The flasks with necks like swans. How a bent glass neck showed that microbes come from other microbes.
- Lightning in a flask. How sparks in a glass loop made some of the building blocks of life.