The Incredible Shrinking Genome 113
Shipud writes "Mammalian genomes have been shrinking for about 65 million years, roughly since the dinosaur extinction. Why? And why were ancient mammalian genomes three times larger than they are today? A new article in Genome Biology and Evolution tries to explain this bizarre finding, and why the genomes of mammals (but not of other living groups) are still shrinking. 'Once [the dinosaurs] were gone, mammals started to radiate, fill those niches, and a whole new level of competition arose. The selective advantage of not having a genome encumbered by potentially damaging mobile DNA elements has probably become critical at this "be ye fruitful and multiply; bring forth abundantly in the earth, and multiply therein" stage. In effect, the genomes of mammals has been shrinking by removing mobile DNA elements, just after the KT boundary. And according to the model presented in this study, this process is still ongoing: mammalian genomes are not at an equilibrium size. Unlike flies, mammals are still cleaning up.'"
Comment removed (Score:5, Insightful)
Re:entropy is winning (Score:2, Insightful)
Re: The Incredible Shrinking Genome (Score:4, Insightful)
We still haven't shed the genes that make some people become Politicians...
There fixed that for you...
I can code that human in 44, maybe 42 chromosomes (Score:1, Insightful)
Sounds like some (open) source I hacked on years ago -- kept finding ways to take (stupid) things out without losing functionality.
Re:entropy is winning (Score:5, Insightful)
Wrong. There is no better or worse in evolution. What is good one day sucks when the environment changes. Evolution is not directed towards anything, it can not progress or retreat. There is no 'should have died young.' There is no natural and unnatural. By helping people procreate who might not have, all we are doing is changing the selection criteria, which are changing all the time anyhow.
However, you got the first part wrong too (assuming you are the same AC) The mammalian genome is not losing information that is valuable, it is losing genetic parasites. The genome has been throwing out the trash that tends to muck things up.
General difficulty of preserving a "life-program" (Score:4, Insightful)
As a thought experiment, imagine the genome to be a very big, very modular program, with lots of clusters of specialized subclasses of functionality that are occasionally or potentially useful.
This program is represented by a coding sequence of molecules; at essence a copyable and readable bitstring.
Time and living in a complex, energetic environment tend to break down complex structures which must be "binary-precise" to maintain their meaning. All else being equal, a longer program, a longer bitstring, has a higher probability of losing parts of itself to mutation. Longer programs; longer genomes, require cleverer techniques to preserve themselves over evolutionary time scales.
The cool thing is, longer programs are precisely those that have the capacity to implement cleverer strategies for keeping their own program information reliably preserved.
That is the essential battle that life and evolution wage against entropy;
More bits (longer genome) = more or better strategies for building bit-containers (organisms) and better strategies for taking advantage of environments or pacifying environments.
But more bits = harder to preserve without critical errors breaking the program.
The life bitstrings are in different states of adaptation to their environment as time passes and both environments and genomes change. In a dynamic environment (or a wide, general niche) more modules and subclasses (waiting in the wings, ready for activation if needed) is probably advantageous to a set of generations of the organism, whereas in a highly adapted state in a stable environment, and an environment with well established niches and in fact cross-supporting functions of those niches (a long-lived relatively stable ecosystem in relatively stable climate), the extra adaptability may carry costs of it being too difficult to retain that extra information reliably for the potential benefit it might have if things changed. The extra program bits can also be dangerous. Most organized variants of code-sections of the life-program are organism-killers, most of the time.
In summary, a longer bitstring at the core of life can only be supported by evolution if it earns its keep in life-preserving strategy execution.
I think life bitstrings (genomes) on Earth have GENERALLY been growing by 1 or 2 bits a year since life began (give or take an enormous waffle factor). But in some, relatively stable, organism-environment pairings, temporary program shortening trends may be advantageous prunings of the more wild-ass life mechanism "ideas".
Re:entropy is winning (Score:5, Insightful)
No, we don't mean progress towards something 'better'.
Evolution proceeds only towards a local optimum, never towards anything abstractly 'better' or 'more perfect'. Evolution has no interests, long term goals, or overall arrow of direction. That's standard. That's the version of the theory Darwin and Wallace framed, that's what Sir Francis Crick assumed to be true doing his work, that's what Richard Dawkins would argue right now.
Those same people would tell you evolution is not affected in the slightest by people changing environmental conditions so that some things which were once major disadvantages are not anymore, and that there is no 'should have died' in the theory.
I say this, because I disagree with some ideas people, including some prominent scientists, legitimately think are part of the theory. But usually if I bring that up on slashdot, I get negative modded to oblivion by people just like you. It's like being modded down for disagreeing with the "Standard Democratic Party" line, only to find out that the guys doing it also claim that party-line is "Strong spending for defense, no money for social programs". I never get to debate or discuss any real issues relating to Evolution, because by the time somebody who understands and agrees with the real theory is reading this thread, the whole topic will have drowned under dozens of mods from people who think they are defending Evolution from "Weirdo Creationists", when what they are defending is a weirdo theory with progress, devolution, and a bunch of other kerfluffle that has nothing to do with science.
Re:It's the Right Idea (Score:2, Insightful)
This explains why the Vikings conquered the Mediterranean where the Assyrians, Hittites, Egyptians, Greeks, and Romans failed so miserably to make much of any kind of impression on history, and how the North Americans, who came from Asia and were the farthest removed from Africa, conquered the Europeans who were so much closer to Africa and had interbred with the dirty Neanderthals. Ditto for the Australians, who were also so far removed from Africa and conquered Europe too.
Don't laugh.
Look at how far we go to make sure medeival thugs who want to drag us all back about 1300 years don't get "offended".
Yeah, I'm talking about fundamentalist Islam.
Go ahead, mod me down. Kowtow to political correctness and chalk up stoning gays and subjugating women as "diversity" while you mock "ignorant Christians" and congratulate yourself on how "tolerant" you are.
As Blaise Pascal put it... (Score:5, Insightful)
The watchmaker has had more time...
Re:entropy is winning (Score:2, Insightful)
But usually if I bring that up on slashdot, I get negative modded to oblivion by people just like you.
Why on Earth would this bother you at all?
Re:Evolution and progress (Score:4, Insightful)
Quoted from the wiki page on Darwin's Dangerous Idea:
The first chapter of part II, "Darwinian Thinking in Biology", asserts that life originated without any skyhooks, and the orderly world we know is the result of a blind and undirected shuffle through chaos.
That's all I'm saying. Adaptation is a continual process. As creatures adapt, they change their environment, which changes the selection criteria. Are wings 'progress?' Not to a worm. Are eyes? Not to a cave fish. Any thing in evolution that you can point to as 'progress,' I can point to a counter example where the exact same thing would be a liability.