April 08, 2004
DNA Error Checking Evolves
debate about mutation brought an idea to mind. Here it is for you guys to shoot down if I'm "out to lunch."
During times that the environment is stable - the climate is stable and and a particular species' niche is well-defended and other niches are unavailable, there is selective pressure to improve error checking within that species so as to decrease mutations. This slows evolution to a crawl.
When the environment is unstable there is selective pressure to decrease DNA error checking. This will speed evolution.
This is how the selective pressure is brought to bear:
Let's say two individuals, A and B, are born into a species that is well-adapted to a niche within a stable climate and other niches are unavailable. A is born with DNA error checking efficiency of 95% and B has DNA error checking efficiency of 97%. Other than this difference let's assume that A and B are identical. Let's also assume that both A and B are successful at having children and that their children inherit the DNA error checking efficiency of their respective fore-bearers.
As time passes B's descendents will be marginally more successful than A's descendents. Why? Because B's family will have fewer mutants. And a mutation is not likely to be beneficial when the climate is stable and the niche is well-defended and other niches are unavailable. Under these circumstances greater error checking efficiency is a positive adaptation. B's family prospers as A's family begins to lose ground to B.
But then something happens. The climate changes, the dinosaurs are wiped out, whatever. Both the population of family A and family B plummet. But after a long time it is A's family that rebounds while family B flirts with extinction. Why? Family A is in a better position to quickly adapt to the changing environment. Family A has more mutants than B and any given mutation has a greater chance of being beneficial in this new environment. The old adaptations no longer serve in the new environment. Both A and B must change, but A is better able to do so.
In times of crisis niches will open up. Family A will also be in a better position to exploit the new ground.
This idea is almost certainly old news. Could someone point me to more information on it?
Posted by Stephen Gordon at 12:39 AM
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April 05, 2004
Evolution: We Ignore It At Our Peril
Matt of mattandnancy.org
wrote the following in a comment to "It's Life Jim
Evolutionary theory has the same problem [it cannot be observed or subjected to experiment]. We have NEVER witnessed an organism going from simple to more complex, i.e., the generation of new DNA information, we have only witnessed speciation (Darwin's finches). We witness destructive evolution, not creative evolution. In thermodynamics would be called entropy...
It takes as much faith (I would argue that it takes more) to believe in evolution as it takes to believe in creationism.
I disagree. Scientists today can actually watch evolution take place in front of them. There are experimenting with its mechanisms everyday in the lab.
When Darwin first published his theory he assumed that it would always be impossible to watch evolution take place. He assumed that evolution occurred at such a slow pace that it was the biological equivalent of geology - that it was such a slow process that it could only be appreciated by examining the fossil record.
Even back then there were some famous examples of quick change though. There was a species of moth in England that was a light gray that matched the brick of homes and buildings. As the industrial revolution piped black soot into the atmosphere (and blackened the buildings), the moth became dark as well. It turns out that the moth was depending upon camouflage to allude their predators – birds. As the buildings darkened, those moths that were born a little darker had a better chance of surviving to reproduce – thus passing along the darker trait. This way each generation (and the generations come very fast with moths) quickly became darker.
As fast as generations come with moths, they are nothing in comparison to bacteria. Now, biologist who examine microscopic life can watch evolution take place very quickly in their laboratories. Everyone is familiar with how flu changes every year – thereby alluding last year's flu shot. And crops that were once protected by certain pesticides now require more pesticide (both in quantity and in toxicity) to provide the same protection.
One benefit of accepting evolution and coming to understand how it works will be in finding better solutions to these arms races (the disease v. vaccine or antibiotic race; and the crop pests v. pesticide race). Carl Zimmer gives the following example in his book "Evolution." There is a group of ant species that are fungus farmers
. These ants have been farming fungus for millennia. Scientists know this has been going on a long time because the original fungus-farming ant has now split into several fungus-farming subspecies.
Here's the point – some of these species protect their fungus crop with their version of a pesticide – a bacteria which is carried on the ant's legs. This bacterial pesticide has provided protection of fungal crops for millennia (enough generations for the fugal farming ant to split into different species that all use the same bacteria). The ant's bacteria is still providing crop protection after all these years while we humans are having problems with pesticide resistance after a single human generation. What gives?
Well, unlike a toxin, bacteria are alive. The bacterial pesticide is evolving along with the pest. If the pest adapts to the bacteria, the bacteria adapt to the pest. Around and around it goes.
We should protect our crops with a similar strategy. Of course moving to this sort of crop protection will require a general acceptance of the rationale behind the move – evolution. The alternative is bleak. The alternative is to continue to lose more crops every season to pests while using more and more toxins against them.
Posted by Stephen Gordon at 10:46 AM
| Comments (36)
March 02, 2004
It's "The Champaign Pyramid of Life," Simba
In a comment to "The Fog
" post below, Phil stated,
Evolution does not work towards fitness alone… bacteria are often as fit (if not more fit) than human beings. Evolution seems to work towards optimal fitness within increasingly complex designs. If evolution was concerned only with fitness, there would be as many examples of complex creatures devolving to simpler forms (which happen to be more "fit") as there are of simpler creatures evolving towards more complex forms. But I'm not aware of any such examples, leading me to conclude that either:
1. There is always an evolutionary advantage to greater complexity.
2. Evolution simply runs towards the more complex.
I'm choosing option number two.
If there were an evolutionary advantage to greater complexity, I would expect to see no bacteria left in the environment – they would be out-competed by the more complex life forms. Of course, bacteria are still everywhere. So I have to think about option number two.
Phil makes an important point about de-evolution – it doesn't happen. Complexity is a one-way ratchet. I think the easiest answer to this is that nature doesn't have a good eraser. If the environment changes, all surviving life forms will become more complex in an effort to adapt, never less complex.
It's like a Champaign pyramid
where the top glass represents the least complex form of life. Before levels of increasing complexity are filled, the simpler level above must be filled. The simpler levels are not abandoned as the lower more complex levels fill. Simple gives birth to complex, but complex can never give birth to simple. DNA would no sooner abandon its precious store of information than Champaign would flow uphill.
The only eraser is extinction. If a species grows too complex for it's environment, perhaps by being too highly adapted to a narrow biological niche, then environmental change might wipe the species out. But extinction is not directly recorded into the DNA of anything alive today. Nothing alive today descends from an evolutionary dead-end.
And so DNA is the ultimate spaghetti
. Patched-on "it'll do" solutions have been cobbled together sometimes to solve problems we no longer have. People in industrialized nations, for example, are struggling with obesity because our metabolism is so thrifty - an unneeded gift from our starving ancestors.
Posted by Stephen Gordon at 02:51 PM
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