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I continue to be amazed at how many people either don’t understand just what evolution is, or don’t communicate what it is very well at all. The recent news of a species of E. coli bacteria that now ‘eats’ citrate is a prime example. Here’s an excerpt from the linked article:

In nature, there have been a few reports of E. coli that can feed on citrate. But these oddballs all acquired a ring of DNA called a plasmid from some other species of bacteria. Lenski selected a strain of E. coli for his experiments that doesn’t have any plasmids, there were no other bacteria in the experiment, and the evolved bacteria remain plasmid-free. So the only explanation was that this one line of E. coli had evolved the ability to eat citrate on its own.

The way that’s stated, “this one line of E. coli had evolved the ability to eat citrate on its own,” it sounds as if the line of E. coli had taken some action to develop that ability. E. coli didn’t take any action beyond living, reproducing, and dying. The citrate-eating ability showed up in one flask of many after more than 33,000 generations. Somewhere along those many generations, a mutation that allowed the cell membranes of one E. coli bacterium to pass the larger citrate molecule through took place. That one bacterium passed that genetic trait on to at least some of its offspring, who passed it along to some of their offspring, and so on.

In a closed environment (a lab flask in this case), the population of E. coli reaches a certain point and then maxes out because the environment won’t support any more. But as more bacteria gained that citrate-eating trait, the environment could support a higher population. The mutant bacteria could utilize both the glucose that every E. coli bacterium could utilize and the citrate that only the mutant bacteria could. They were better equipped, because of a random mutation, to utilize the nutrients in the environment than the non-mutant E. coli were, so their numbers increased while the non-mutant population decreased from lack of suitable nutrients to sustain reproduction. The bacteria didn’t do anything to cause the new trait. They just capitalized on its presence by surviving and reproducing.

What isn’t said is that there were undoubtably many, many other mutations that occurred over the 33,000 generations. But they were mutations that didn’t provide any advantages over the normal genetic makeup of the bacteria. Those mutant bacteria didn’t have a survival edge over the non-mutant bacteria, so they lived and died like the non-mutant bacteria. Evolution is survival of the fittest, and only occurs when a mutation provides some kind of survival benefit in the environment where it occurs. Having cell membranes that allowed larger molecules to pass through was a survival benefit in that environment where citrate was apparently the only ‘large’ molecule to be found. Had some other ‘large’ molecule that was detrimental to the bacterium’s survival been present, the mutated bacterium would likely have failed to live long enough to pass that genetic trait along and the ability to eat citrate would have died along with it.

So, a change in environment can end the advantage a particular genetic trait gives to the organism that has it. The evolutionary process is tied to genetic traits that provide certain abilities in certain environments. Change the environment and the process is altered, sometimes to the detriment of the organism involved. How many species died during an ice age because they lacked the genetic traits that allowed survival and reproduction at colder temperatures? How many species died when the climate got warmer because they lacked the genetic traits that allowed survival and reproduction at hotter temperatures?

The evolutionary process is also tied to the number of mutations that occur, which is dependent on the number of offspring produced. Number of offspring increases in two ways. More generations of offspring and more offspring per generation. It may be that had the E. coli been bred in a larger environment, the number of generations it took for the citrate-eating genetic trait to occur might have been smaller (larger number of offspring per generation), because an equivalent number of offspring had been produced.

Evolution seems to be the province of the winners of the cosmic crapshoot of mutation. There are untold billions of mutations that did not provide any survival benefit in the environment where they occurred. Only the mutations that provided a survival benefit in some kind of genetic trait that was passed along to the next generation are part of what ends up being called the evolutionary process.

One can observe the changes wrought by mutation along the way, but only when the changed survive and reproduce better than the unchanged can one describe it as evolutionary. Evolution is not a play-by-play one can report as it goes along. It is history, observed in retrospect.