How Predictable Is Evolution? 209
sciencehabit (1205606) writes "If the clock rewound, would organisms evolve the same way they did before? Humble stick insects may hold the answer to that long-running question in biology. Through studies of these bugs, whose bodies match the leaves the insects live on, researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low,' says Andrew Hendry, an evolutionary biologist at McGill University in Montreal, Canada, who was not involved with the work."
Repeatable as Fuck (Score:2, Interesting)
Just look at how many times Eyes have independently evolved, yet they all have the same basic components.
We put water, methane, CO2, etc. in a closed system, ran some simulated "lightning" through, and got amino acids and what not forming. Various experiments show similar (even more prominently supporting) results: Nature and physics shapes the beings that exist within it.
There are plenty of other examples of evolution coming to similar results from different ends -- Just look at the shapes of sharks and whales. Not going to further dignify this anti-intellectual ignorant rubbish. Use a damn search engine, that's what we built the web for.
Re:Repeatable as Fuck (Score:5, Interesting)
This tells us that getting a sensor is repeatable. There are high-level design details of eyes that are divergent across species. The "blind spot" is a flaw in the eye design that is shared by all vertebrates, but cephalopods don't have it. Either it's very hard to mutate our way out of the flaw, or the flaw is by itself not important enough for the extraordinarily rare mutants who evolve their way past it to gain any ground on non-mutant populations.
It's easy to think of that as an accident of fate, and eventually such accidents are bound to build up into going a different direction in response to strong selection pressures.
I think sharks and dolphins is better than sharks and whales. That demonstrates convergent evolution -- but note that dolphins still have lungs, and sharks still have gills. They got to similar body plans but they are not fundamentally the same.
It depends... (Score:5, Interesting)
The degree of molecular similarity in the DNA changes to achieve a particular result will depend strongly on the type of change one is looking at.
For the case of toxin-resistance, which is much closer to the molecular level, the odds of similar changes to the DNA are much higher than for complex morphological changes.
Molecular changes like toxin-resistance are more likely to involve a single gene that codes for a single enzyme, changing the enzyme so that the toxin is no longer metabolized in a harmful way. There are going to be a very limited number of ways to do this because it's pretty close to a one-gene/one-enzyme mapping in many cases.
Morphological changes, on the other hand, involve a whole network of genes that are turned on over the course of development, and the network can be altered in many different ways to get to the same result. Think about it like a road network where you're used to taking a particular route to get from A to B. If a bridge goes out on your your usual route, you may choose different alternatives depending on time of day, the kind of vehicle you drive, etc. Networks create choices.
Even then it will depend on the kind of morphological change we are talking about.
For example, there is a lizard in Mexico, which was studied in the '80's or '90s. There were several related species living inland, and a couple of isolated species on the coast near the Yucatan peninsula. Both the coastal species had an extra cervical (neck) vertebra, and it had been assumed on the basis of this similar morphology that their evolutionary history had been a general migration to the coast, an adaptation to coastal environments that involved having a longer neck, followed by a general die-back that resulted in the two existing but separate populations.
It turns out based on their genes the two coastal species hadn't had a common ancestor for millions or tens of millions of years, and the adaptation to coastal living had happened independently but fairly recently. In this case, because certain aspects of body plan are controlled by a highly conserved and relatively simple set of genes, the additional vertebra were the result of similar sets of genetic changes.
Things like body width, which is what TFA is talking about, are a lot more complicated in their regulation, so more likely to be achieved via different genetic changes that have the same morphological outcome.
I'm going to throw in a shameless plug here because it seems relevant to the topic at hand. I've just published a hard SF novel that's premised on a what-if about the role of mathematics and law-like descriptions in evolution. If you're interested in that sort of thing you should check it out: http://www.amazon.com/Darwins-... [amazon.com]
What? (Score:5, Interesting)
If I'm reading this wrong, and I hope I am, please let me know.
...researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low...
I read this as "Stick bugs have reached similar appearances through different means thus the same change probably won't make the same result".
Is this equivalent to "People can change their appearance to include a hole in the abdomen through different means (bullets and knives). Thus shooting or stabbing people are unlikely to produce holes in people"?
It may make it more difficult to guess which DNA change caused them to look like that (without an actual DNA test), but it in no way implies that those DNA changes won't necessarily cause them to look like that.
Burgess Shale (Score:3, Interesting)
Well, I'm not explaining it right, but that's why there's books...
Re:Repeatable as Fuck (Score:5, Interesting)
also could have mentioned some bird's eyes that can see the earth's magnetic field; and goats with their horizontal rectangular pupils, which combined with the eyes position on the skull gives them a 340 degree field of vision without even having to move their eye. they can see you coming up behind them!
Re: Bah (Score:5, Interesting)
There's a great book by the artist Wayne D. Barlowe, called "Expedition". it shows the life forms of a fictional planet called Darwin 4 . With dense atmosphere and low gravity, Everything evolves big, and almost nothing has anything like eyes (sonar is both popular and often very advanced). Without giving too much away for those who still haven't run across this, there are several common body plans that tend to run through whole phyla, and which don't occur on Earth, but make really good sense on Darwin 4. The underlying science is generally sound - I base this on the way various people who have read it point to this or that creature as less probable than the others, but seem to pick out different ones. This book has become my standard for SF aliens.