Mutation biological and otherwise

Here’s another lesson from biology. Again it’s not a biology lesson but a cursory, semi-informed look at scientific research that, I for one find, inspiring or possessing (non-scientific) existential value for further meditations.

In this fascinating, real-life experiment it’s discovered that a life-enhancing mutation was made possible by a seemingly meaningless mutation thousands of generations earlier.

Maybe I should present it in a fictional style — perhaps something along the lines of Zelazny’s Bridge of Ashes. Not that I disagree with the critics who said it wasn’t Zelazny’s best and seemed to agree about its flaws.

Here’s the science story. It’s one I find especially intriguing. Not so much for the implications it has for biologists (not being one myself), or because it may help settle a widely disputed detail in the theory of evolution. For me, it is fascinating as some kind of metaphor, or allegory, or trope — even though I’m not sure what it’s an analogy for. Nonetheless, it strikes me as something very cool and I suspect very important in realms far outside of the field of evolutionary biology.

Consider the famous, on-going E. coli long-term evolution experiment of Richard Lenski and his colleagues.

Since early 1988 Lenski and co. have been busy with their petrie dishes growing and studying the changes in a number of populations of identical bacteria. Back in 1988 they set up 12 genetically identical colonies (these are asexual Escheria coli bacteria — they reproduce by cloning themselves).

A year ago (from the date of my writing this) in April of 2014 they reached their 60,000th generation. That’s quite a few in only a quarter century — in comparison, we (good old Homo saps) are estimated to have had only 20,000 since we got going around 200,000 years ago back in Africa.

As Lenski explains on his website “The main focus of my lab is on experimental evolution. Evolution is usually investigated using the comparative method or by studying fossils. Our approach is to watch evolution as it happens, in the context of experiments that are replicated and performed under controlled conditions… In order to study evolution as it happens requires either a time machine (which we don’t have) or else organisms that replicate, mutate, and evolve very fast, so that we can detect changes on a reasonable time scale.”

Hence, the bacteria.

Of course, this research has led to many interesting insights into evolution. Here’s the one that Lenski thinks is the most astounding and (for far less informed reasons) so do I.

Somewhere around the 31,500th generation genetic changes in one of the colonies of E. coli gave them the ability to metabolize citric acid that was there in the environment (something E. Coli just can’t do).

That new adaptation turned the inedible into the edible, providing a new source of food and leading to an increase in the size and diversity of their population.

Happily, Lenski had a freezer full of samples drawn every 500th generation from each of the 12 populations. These would let him determine whether this new ability was caused by a single, very rare mutation or was the result of, the also very unlikely, accumulation of a number of mutations in the particular sequence they would require for this result.

The results were very weird and quite wonderful (to me, and also to you — I hope).

Using the frozen sample to replay evolutionary history could reveal if this colony would evolve the same adptation and whether any of the other 11 populations would do the same. Replays involving trillions of cells showed only this population developed the mutation and then only when he restarted from after the 20,000th generation. Something happened around generation 20K that opened the way for this new adaptation 5,000 generations later.

It’s as if some mutation happened to one of our ancestors 50,000 years ago that had no impact until today 5,000 generations later when it made possible another new mutation and the ability to do something previously impossible for human beings.

Or if you prefer, that has no results until some distant time when it allows a change that would otherwise be impossible.

Lenski and his team later reported that after 50,000 generations bacteria were continuing to improve their abilities. Comparing the behaviour of all strains with samples from the 10,000 generations earlier the general fitness appeared to be increasing, and showed no sign of slowing down.