Critics of Darwinian theory frequently complain that evolution cannot be directly observed. In fact this has not been true for a long time. Natural selection as a mechanism for change in the forms of organisms has been extensively demonstrated and studied in laboratories. Little Green Footballs directs our attention to a twenty year experiment that has confirmed and enriched our understanding of the major elements in the theory.
His source is science writer Carl Zimmer, who writes about biologist Richard Lenski at Michigan State University.
Lenski started off with a single microbe [Escherichia coli, the common gut microbe]. It divided a few times into identical clones, from which Lenski started 12 colonies. He kept each of these 12 lines in its own flask. Each day he and his colleagues provided the bacteria with a little glucose, which was gobbled up by the afternoon. The next morning, the scientists took a small sample from each flask and put it in a new one with fresh glucose. And on and on and on, for 20 years and running.
So from one E Coli Jacob, Lenski produced twelve tribes. Then he changed their environment by adding the sugar. He has had twenty years to see how the microbes would adapt to the new environment.
Based on what scientists already knew about evolution, Lenski expected that the bacteria would experience natural selection in their new environment. In each generation, some of the microbes would mutate. Most of the mutations would be harmful, killing the bacteria or making them grow more slowly. Others would be beneficial allowing them to breed faster in their new environment. They would gradually dominate the population, only to be replaced when a new mutation arose to produce an even fitter sort of microbe.
But how do you keep track of what is actually happening? How do you know what is due to new information introduced by mutation, and what is due to previously unsuspected traits of an existing population?
Lenski used a simple but elegant method to find out. He froze some of the original bacteria in each line, and then froze bacteria every 500 generations. Whenever he was so inclined, he could go back into this fossil record and thaw out some bacteria, bringing them back to life. By putting the newest bacteria in his lines in a flask along with their ancestors, for example, he could compare how well the bacteria had adapted to the environment he had created.
This is evolution observed and tested. Lenski could constantly compare later generations to earlier ones, subject to genetic analysis. And if a population became contaminated by outside organisms (a constant problem), he could restore an earlier, uncontaminated sample. It's a lot like keeping a back up copy of a file.
What Lenski observed is exactly what Darwinian theory leads one to suspect: general adaptation to the environment, driven in part by random mutation.
Over the generations, in fits and starts, the bacteria did indeed evolve into faster breeders. The bacteria in the flasks today breed 75% faster on average than their original ancestor. Lenski and his colleagues have pinpointed some of the genes that have evolved along the way; in some cases, for example, the same gene has changed in almost every line, but it has mutated in a different spot in each case. Lenski and his colleagues have also shown how natural selection has demanded trade-offs from the bacteria; while they grow faster on a meager diet of glucose, they've gotten worse at feeding on some other kinds of sugars.
So a beneficial trait emerged several times in different bacterial tribes. The genes coding for the trait weren't there to begin with. Random mutation is the only explanation for their emergence.
But some traits are easier to get by mutation than others. One of Lenski's bacterial tribes (he would call them colonies) acquired the ability to consume citrate, which is essentially the same compound that makes lemons tart. Unlike the above mentioned mutations, this one happened only once in one colony.
Some critics of Darwinian theory, such as the Intelligent Design school, acknowledge the power of natural selection to modify existing species, but complain that we have never observed speciation, the process by which a new species can emerge from existing ones. Lenski has nailed that one down. How do we know what a species is? How do we tell which organism belongs in which species, or when two populations of creatures deserve to be identified as different species or subspecies? The science of biology has no generally accepted answer to that question, because in almost all cases the boundaries are vague and shifting. Are dogs and wolves two species or one? And what about coyotes? All three creatures interbreed.
It seems relatively easy to distinguish human beings from chimpanzees, but we do so by recognizing the different traits of each species: they are hairy and walk on their knuckles, we are naked and laugh at jokes. But one of the defining species characteristics of Escherichia coli is that it can't eat citrate. In nature, E coli only acquire this ability when they borrow it from other species of bacteria. In Richard Lenski's experiment, Darwinian evolution has produced a new organism that does not fit the definition of any previously existing species of organism. Speciation has been observed in the laboratory.
In the beginning, God created the heavens and the earth. I think that is almost a tautology, though it leaves a lot of open questions about God. But He created it according to a number of basic physical laws, and allowed pointy heads like Lenski to discover them. Evolutionary biologists have been more faithful to the Creator, in their own fashion, than have the critics of Darwin.
For those of us who want to look and things and see what they are, Lenski's work is pure gold.
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