The Polarized Postdoc

Posts Tagged ‘fireflies

Evolutionary noise

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This year I celebrated America´s birthday in style, sitting around with my friends in our beer and burger filled bellies playing the evolution game. Basically, a hand-waving exercise to entertain ourselves whilst fireworks do their natural selection bit around the neighborhood. It consists in picking a natural feature or trait around you (from blue eyes to curved finches), and by applying simple evolutionary rules decide how and why it was preserved to be witnessed by us today. When asked about the rules by the significant non-scientist present, we were able to distill all the beauty and wisdom of Darwin´s theory in a few simple parameters: traits are selected-for, in a given environment, if they confer an advantage for either survival or procreation.

Everything else that comes along for the ride can be considered evolutionary noise. The term defines seemingly useless traits such as the ability to twist your tongue or move your ears. Unless you can do either in a really sexy way that can help guarantee your reproductive success, that is. Unfortunately for me, when I think about evolutionary noise I can not dodge this mental thumbnail of a low deep humming caused by our tail bones retracting and our skulls expanding. But I still love the game.

Of course, when played on a 4th of July evening, fireflies are the first thing to come up.

caught in mid-courtship by the National Geographic

caught in mid-courtship by the National Geographic

We were all pretty close to accurate in speculating that light production, in all its refinement and uniqueness, cannot be a by-product of insect species divergence. The green sparks are, far from noise, a well-tuned performance by the summer dusk orchestra. Our best, almost-educated guess was that flashes play a role in mating and/or prey attraction. This turned out to be true, albeit in a sleek and refined way: flash patterns actually differ from one firefly species to another, allowing the similar looking bugs to recognize a suitable partner. Which is definitely useful, and could even come in handy in some dark human shindigs I know. Moreover, some firefly females use their flash patterns to attract males from other species and eat them. Much like in the aforementioned shindigs, romance is a risky business in the mid summer nights.

From the evolution perspective, firefly light is all quiet, except from the smooching and chewing. The firefly take on “better living through chemistry” fits the profile of a selected-for advantageous adaptation. So maybe to hear the noise one has to come closer, and stare at recent evolution instead of long-hauled characteristics. For that I proposed an example recently learned from population genetics, one of the coolest scientific disciplines. Some weeks ago I had the pleasure to become acquainted with the work of GS Atwal. Simply put, Dr. Atwal uses overly complex statistical tools to dissect the distribution of genetic variants (aka allelles or SNPs in their multiple forms) in different human populations.

It has been known for a while that the genetic background determines susceptibility to certain diseases, including cancer. Population genetic studies are aimed at describing how the different variants appear, often linked to more trackable traits. The population distribution of some faulty variants of tumor suppressor genes correlates with the respective incidence of cancers that stem from the malfunction of the protein encoded by those defective genes. Confronted with this, the question that Atwal asked to climb to the next level of knowledge was how and why, even if they are obviously harmful, do these variants get fixed and stay in the population. Sort of a formal version of the evolution game, without fireworks or fireflies.

At a glance, it would seem like those cancer-prone variants (polymorphisms) are just lousy evolutionary noise. If you apply the rules, these variants do not affect survival of the individual until well after the peak of reproductive age (which is still in the prime of our twenties, biologically speaking). But in collaboration with some eminent geneticists and systems biology experts, Atwal determined that in some cases, the cancerous polymorphisms correlated with a better reproductive success, by increasing fertility rates and facilitating embryonic implantation. These studies in mice reveal an interesting aspect of cancer genetics, the antagonistic pleitropy of some of the genes involved in cancer protection pathways. This concept, while extremely stimulating for future cancer research purposes, is definitely not indicative of evolutionary noise, but of a complex symphony of form and function, shaping the way we perceive natural selection as we grow able to interfere with it. So even when cancer is in play, in the end is Evolution 1, Noise 0.

The score remained tight as well around the dinner table, as we continued to seek out other examples in the warmth of the quieting darkness, and together we lengthy discussed biological sounds of the kind of thumbs and tears and hair and appendixes, with moderate success and plenty of laughter, feeling loved, amused and content. And looking around to capture that moment of sheer perfection, I wondered at the unlikeness of it all, the infinite permutations along the invisible road that led to here, now. It occurred to me right there that the noise might be part of the music of change, entwined with the melody, and that only if they are inextricably blended chance can have a direction.

And I could not help but whisper, trying to entreat the swift moment,

Tarry a while! You are so fair!

Happy 4th of July, everybody.

Written by polarizedpostdoc

July 6, 2009 at 15:15

Posted in personal, science

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