Fossils are not the whole story
When you think of evolution what image first springs to mind? It’s probably a hall in the Natural History Museum filled with fossils. All the dinosaurs, trilobites, coelacanths and ammonites together make an awesome menagerie of extinct creatures. The stepping stones of evolution are laid out before you in rock and bone. But there is something wrong with this picture – it’s just depicting animal evolution which means it is only telling part of the story. There are five other kingdoms of life (plants, fungi, protozoa, bacteria and archaea) and animals showed up relatively recently. Life on Earth started 4 billion years ago but the first animals evolved 0.5 billion years ago, half-way through the last quarter of the game. So that fossil hall in the museum is like a history of the world that only covers one continent in recent time. A history of the world that starts with American Independence and never strays beyond its borders. (Yes. I know. For many Americans that really is the history of the world but bear with me)
Lynn Margulis challenged orthodoxy
Most famous evolutionary biologists (Dawkins, Gould, Haldane, Maynard Smith, etc) come from a background in zoology. Their expertise is in the comparative study of animals. Lynn Margulis, who died aged 73 in November 2012, was different. She was a microbiologist who focused on the evolution of eukaryotic cells (cells with a nucleus) and became convinced that the scientific consensus was wrong. The mainstream thinking was that the engine driving the evolution of species was random genetic mutation in which only the fittest survived. Margulis agreed that natural selection picked winners but disagreed about how the competing variants were created. She believed that evolution was driven by the symbiotic cooperation of organisms: the competitors in the race worked together rather than competed with each other. The mainstream saw the creation of new species as a divergent process; just as twigs and branches diverge from the trunk of a tree. Margulis believed that new species were created by a process of fusion and merger. She wrote a paper about it in 1966 called “ Symbiogenesis: the origin of eukaryotic cells”.
And then nothing happened. In fact, worse than nothing. Fifteen academic journals rejected her paper. One actually said “Your research is crap. Don’t ever bother to apply again”. Maybe it was because she was a woman. Maybe it was her difficult personality and bad temper. After extensive reworking, she finally managed to get her paper published in the Journal of Theoretical Biology. It was a groundbreaking piece of work. For the first time, the evolution of cells had been properly examined: a history of a continent that was not America had been published. The response from the mainstream was…..complete silence. No one bothered to respond because no one really cared.
The theory of symbiogenesis
And then, very gradually, the years passed and data began to trickle in to support her theory. A single cell is more complex than you might imagine; it’s more than a nucleus in a little sack of protoplasm. The diagram below shows that there are 13 different entities inside it. The crucial evidence to support her theory came when scientists discovered that some of these entities had DNA that was different from the nucleus. The DNA of mitochondria, chloroplasts, basal granules and plastids is not the same as the DNA in the nucleus. This implies that a cell, the fundamental building block of all animals, is a fusion of different bacteria-like creatures. At some time in the past, a group of different bacteria clumped together to form a eukaryotic cell. This cell was dramatically more successful that the individuals composing it and became the basis of all higher lifeforms. The living creatures that we see around us all stem from that initial cooperative merger. Nature is not wholly “red in tooth and claw”.
1. Nucleolus
2. Nucleus
3. Ribosome
4. Vesicle
5. Rough endoplasmic reticulum
6. Golgi apparatus (or “Golgi body”)
7. Cytoskeleton
8. Smooth endoplasmic reticulum
9. Mitochondrion
10. Vacuole
11. Cytosol
12. Lysosome
13. Centriole
Lynn Margulis’s theory has now become scientific orthodoxy and her book “Symbiosis in Cell Evolution” is seen as a classic of 20th century biology. Her concept of symbiogenesis could be summarised as
“Today’s groups are tomorrow’s individuals”.
Time acts to drive individuals up the catataxic ladder. In a social history of the world, families become tribes, tribes become nations, nations become empires. So too in biology. Bacteria merge to become eukaryotic cells, single cell creatures merge to become multicellular plants and animals, and the resulting flora and fauna knit together to form complex ecosystems. What you view today as a group of separate but similar things in the fullness of time will be viewed as a single entity.
0 Comments