Tuesday, December 17, 2013

It's Complicated

David Dobbs at Aeon discusses how evolution is a far more complex process than you were taught in high school.

In fact, in reading this article one wonders how such complexity - complexity that can only be explained in terms of metaphors that trade on intelligent guidance - could ever have arisen in the first place.

Dobbs focuses on the complexity of the genome (the genetic blueprint of an organism) and how the popular understanding of the gene as the unit of inheritance is to the actual state of affairs as a playground one-on-one basketball game is to an NBA contest.

It's turning out that the classical view of evolutionary change, which held that genetic mutation causes phenotypic alterations (alterations in the physical appearance or behavior of an organism) which are then sifted by the environment according to the "fitness" they conferred, is backwards. Actually, it looks like changes often occur in the phenotype first and are fixed in the genome generations later. Here's Dobbs' lede:
A couple of years ago, at a massive conference of neuroscientists — 35,000 attendees, scores of sessions going at any given time — I wandered into a talk that I thought would be about consciousness but proved (wrong room) to be about grasshoppers and locusts. At the front of the room, a bug-obsessed neuroscientist named Steve Rogers was describing these two creatures — one elegant, modest, and well-mannered, the other a soccer hooligan.

The grasshopper, he noted, sports long legs and wings, walks low and slow, and dines discreetly in solitude. The locust scurries hurriedly and hoggishly on short, crooked legs and joins hungrily with others to form swarms that darken the sky and descend to chew the farmer’s fields bare.

Related, yes, just as grasshoppers and crickets are. But even someone as insect-ignorant as I could see that the hopper and the locust were radically different animals — different species, doubtless, possibly different genera. So I was quite amazed when Rogers told us that grasshopper and locust are in fact the same species, even the same animal, and that, as Jekyll is Hyde, one can morph into the other at alarmingly short notice.

Not all grasshopper species, he explained (there are some 11,000), possess this morphing power; some always remain grasshoppers. But every locust was, and technically still is, a grasshopper — not a different species or subspecies, but a sort of hopper gone mad. If faced with clues that food might be scarce, such as hunger or crowding, certain grasshopper species can transform within days or even hours from their solitudinous hopper states to become part of a maniacally social locust scourge. They can also return quickly to their original form.

In the most infamous species, Schistocerca gregaria, the desert locust of Africa, the Middle East and Asia, these phase changes (as this morphing process is called) occur when crowding spurs a temporary spike in serotonin levels, which causes changes in gene expression so widespread and powerful they alter not just the hopper’s behaviour but its appearance and form. Legs and wings shrink. Subtle camo colouring turns conspicuously garish. The brain grows to manage the animal’s newly complicated social world, which includes the fact that, if a locust moves too slowly amid its million cousins, the cousins directly behind might eat it.

How does this happen? Does something happen to their genes? Yes, but — and here was the point of Rogers’s talk — their genes don’t actually change. That is, they don’t mutate or in any way alter the genetic sequence or DNA. Nothing gets rewritten. Instead, this bug’s DNA — the genetic book with millions of letters that form the instructions for building and operating a grasshopper — gets reread so that the very same book becomes the instructions for operating a locust. Even as one animal becomes the other, as Jekyll becomes Hyde, its genome stays unchanged. Same genome, same individual, but, I think we can all agree, quite a different beast.


Transforming the hopper is gene expression — a change in how the hopper’s genes are ‘expressed’, or read out. Gene expression is what makes a gene meaningful, and it’s vital for distinguishing one species from another.
The same DNA in both insects is "read" differently in different environmental conditions producing radically diverse animals. It's as if one could read Crime and Punishment by reading every third word of Brothers Karamazov. Such a novel would be a sign of unimaginable genius in the author and yet we're all expected by our cultural betters to believe that such a phenomenon arose in living cells purely by blind, purposeless, serendipitous happenstance.

The article is long but it's must-reading for anyone interested in biology.