Gene egoísta: mais uma especulação darwinista jogada na lata de lixo da História da Ciência

sexta-feira, dezembro 06, 2013

Die, selfish gene, die

The selfish gene is one of the most successful science metaphors ever invented. Unfortunately, it’s wrong

by David Dobbs

Grasshopper (Acrididae), Barbilla National Park, Costa Rica. Photo by Piotr Naskrecki/Minden Pictures/Corbis

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 wildly 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. We humans, for instance, share more than half our genomes with flatworms; about 60 per cent with fruit flies and chickens; 80 per cent with cows; and 99 per cent with chimps. Those genetic distinctions aren’t enough to create all our differences from those animals — what biologists call our particular phenotype, which is essentially the recognisable thing a genotype builds. This means that we are human, rather than wormlike, flylike, chickenlike, feline, bovine, or excessively simian, less because we carry different genes from those other species than because our cells read differently our remarkably similar genomes as we develop from zygote to adult. The writing varies — but hardly as much as the reading.

This raises a question: if merely reading a genome differently can change organisms so wildly, why bother rewriting the genome to evolve? How vital, really, are actual changes in the genetic code? Do we even need DNA changes to adapt to new environments? Is the importance of the gene as the driver of evolution being overplayed?

You’ve probably noticed that these questions are not gracing the cover of Time or haunting Oprah, Letterman, or even TED talks. Yet for more than two decades they have been stirring a heated argument among geneticists and evolutionary theorists. As evidence of the power of rapid gene expression mounts, these questions might (or might not, for pesky reasons we’ll get to) begin to change not only mainstream evolutionary theory but our more everyday understanding of evolution.

Twenty years ago, phase changes such as those that turn grasshopper to locust were relatively unknown, and, outside of botany anyway, rarely viewed as changes in gene expression. Now, notes Mary Jane West-Eberhard, a wasp researcher at the Smithsonian Tropical Research Institute in Costa Rica, sharp phenotype changes due to gene expression are ‘everywhere’. They show up in gene-expression studies of plants, microbes, fish, wasps, bees, birds, and even people. The genome is continually surprising biologists with how fast and fluidly it can change gene expression — and thus phenotype.

These discoveries closely follow the recognition, during the 1980s, that gene-expression changes during very early development — such as in embryos or sprouting plant seeds — help to create differences between species. At around the same time, genome sequencing began to reveal the startling overlaps mentioned above between the genomes of wildly different creatures. (To repeat: you are 80 per cent cow.)





"Yet West-Eberhard understands why many biologists stick to the gene-centric model. ‘It makes it easier to explain evolution,’ she says. ‘I’ve seen people who work in gene expression who understand all of this. But when they get asked about evolution, they go straight to Mendel. Because people understand it more easily.’ It’s easy to see why: even though life is a zillion bits of biology repeatedly rearranging themselves in a webwork of constantly modulated feedback loops, the selfish-gene model offers a step-by-step account as neat as a three-step flow chart. Gene, trait, phenotype, done.

"In other words, the gene-centric model survives because simplicity is a hugely advantageous trait for an idea to possess. People will select a simple idea over a complex idea almost every time. This holds especially in a hostile environment, like, say, a sceptical crowd."


Queria ver a cara de alguns cientistas evolucionistas da Nomenklatura científica internacional e tupiniquim e da Galera dos meninos e meninas de Dawkins que fizeram da especulação transformista genecentrista egoísta como um dos mecanismos evolucionários explicando a origem, diversidade e complexidade de todas as formas biológicas! 

Alô meu bom amigo Charbel Niño El-Hani. Lembra que você me disse lá na Universidade Presbiteriana Mackenzie, campus São Paulo, SP, que eu tinha embarcado numa canoa furado por defender e propor a teoria do Design Inteligente? Lembra de minha resposta? Que eu tinha deixado o pangaré de Darwin e apostado todas as minhas fichas no cavalo do Design Inteligente? Naquela ocasião a especulação transformista de Richard Dawkins - o GENE EGOÍSTA era aceito e propalado como ciência.

Fui, cada vez mais convencido, que a teoria da evolução de Darwin através da seleção natural e n mecanismos evolucionários (de A a Z, vai que um falhe...) está mais furada do queijo suíço!