My earlier post on the origins of complexity sparked an interesting and informative discussion in the comments so I thought I would pass on another article about it by Amy Maxmen that I came across later, that looked at the same question in light of what we know about the seemingly lowly amoeba. She starts by posing the problem.
Amoebas are puny, stupid blobs, so scientists were surprised to learn that they contain 200 times more DNA than Einstein did. Because amoebas are made of just one cell, researchers assumed they would be simpler than humans genetically. Plus, amoebas date back farther in time than humans, and simplicity is considered an attribute of primitive beings. It just didn’t make sense.
The idea of directionality in nature, a gradient from simple to complex, began with the Greeks, who called nature physis, meaning growth. That idea subtly extended from changes over an organism’s lifetime, to changes over evolutionary time after Charles Darwin argued that all animals descend from a single common ancestor. When his contemporaries drew evolutionary trees of life, they assumed increasing complexity. Worms originated early in animal evolution. Creatures with more complex structures originated later. Biologists tweaked evolutionary trees over the following century, but generally, simple organisms continued to precede the complex.
She says that new studies of genomes cast doubt on earlier ideas that complexity, at least as measured in the number of genes possessed by an organism, grew in a linear fashion with time. “The results suggested that complex body parts evolved multiple times and had also been lost. One study found that winged stick insects evolved from wingless stick insects who had winged ancestors.”
She also looks at comb jellies, an organism more complex than sponges that predated the latter, and other animals that reveal that evolution can drive systems to more or less complexity, depending on which is more suited. As a result, things that we think of as singular events in evolution, like the emergence of a central nervous system, may have evolved more than once.
“Traditional views are based on our dependence on our nervous system,” says [evolutionary biologist Joseph] Ryan. “We think the nervous system is the greatest thing in the world so how could anything lose it,” he says. “Or, it’s the greatest thing in the world, so how could it happen twice.”
It is an interesting article that contained fascinating new information (for me at least) about creatures and their features that I was not aware of before.