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Medicine Science

Prions Evolve Despite Having No DNA 214

Posted by kdawson
from the wipe-that-foam-off-your-mouth dept.
An anonymous reader writes "Scientists from the Scripps Research Institute have shown for the first time that 'lifeless' organic substances with no genetic material — prions similar to those believed responsible for Mad Cow disease and similar, rare conditions in humans — are capable of evolving just like higher forms of life. The discovery could reshape the definition of life and have revolutionary impacts on how certain diseases are treated."
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Prions Evolve Despite Having No DNA

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  • by Anonymous Coward on Sunday January 10, 2010 @06:05AM (#30713630)

    Don't get me wrong, dna has some neat copying-related properties... but evolution is not about dna. The idea came along long before the physical basis of human heredity was understood, and it is a far more general principle. To get evolution via natural selection, all you really need is:
    1. Variation
    2. ... that is heritable ( prions, dna, epigenetic markers, and cultural practices all have this to some extent or another)
    3. and something that ensures differential survival (as simple as limited resources).

    These aren't very hard criteria to fulfill. The sticking point is really the heritability bit, but once prions work out the "how to propagate more of me" problem, evolution comes along for the ride.

  • Re:Not Surprised. (Score:4, Informative)

    by MichaelSmith (789609) on Sunday January 10, 2010 @06:31AM (#30713682) Homepage Journal

    Fire has a symbiotic relationship with some plants in Australia. The plants help start fire. The fire kills the plants competitors, including other plants and humans.

  • by MPAB (1074440) on Sunday January 10, 2010 @07:28AM (#30713824)

    Here are the criteria for brain death. An in the case of children, they must be consistent with repeatedly flat EEGs throughout 48 or 72 hours depending on the place. Also, barbiturate and BZD intoxication must be ruled out.

            * Unresponsiveness
                        o The patient is completely unresponsive to external visual, auditory, and tactile stimuli and is incapable of communication in any manner.

            * Absence of cerebral and brain stem function
                        o Pupillary responses are absent, and eye movements cannot be elicited by the vestibulo-ocular reflex or by irrigating the ears with cold water.
                        o The corneal and gag reflex are absent, and there is no facial or tongue movement.
                        o The limbs are flaccid, and there is no movement, although primitive withdrawal movements in response to local painful stimuli, mediated at a spinal cord level, can occur.
                        o Apnea Test: An apnea test should be performed to ascertain that no respirations occur at a PCO2 level of at least 60 mmHg. The patient oxygenation should be maintained with giving 100% oxygen by a cannula inserted into endotracheal tube as the PCO2 rises. The inability to develop respiration is consistent with medullary failure.
            * Nature of coma must be know
                        o Known structural disease or irreversible systemic metabolic cause that can explain the clinical picture.
            * Some causes must be ruled out
                        o Body temperature must be above 32 C to rule out hypothermia
                        o No chance of drug intoxication or neuromuscular blockade
                        o Patient is not in shock
            * Persistence of brain dysfunction
                        o Six hours with a confirmatory isoelectric EEG or electrocerebral silence, performed according to the technical standards of the American Electroencephalographic Society
                        o Twelve hours without a confirmatory EEG
                        o Twenty-four hours for anoxic brain injury without a confirmatory isoeletric EEG

            * Confirmatory tests (are not necessary to diagnose brain death)
                        o EEG with no physiologic brain activity
                        o No cerebral circulation present on angiographic examination( is the principal legal sign in many European countries)
                        o Brain stem-evoked responses with absent function in vital brain stem structures

  • by CxDoo (918501) on Sunday January 10, 2010 @07:51AM (#30713876)

    And iterative improvement based on external definition of 'improvement' (in other words, selection) doesn't presuppose either 'natural' or 'self'.
    Cars evolve. Societies evolve. And so on.
    Life is defined by metabolism & self replication, not evolution.

  • Re:Matter. (Score:3, Informative)

    by magsol (1406749) on Sunday January 10, 2010 @10:29AM (#30714390) Homepage Journal
    Actually, according to the Gibbs free energy equation, it is in fact the opposite: matter's mission to attain a lower energy level, which equates to an increasing amount of disorder in the system. Finding a "greater order", on the other hand, requires an input of energy to the system.

    Evolution is a large-scale byproduct of adapting to the changing environment in such a way that is energetically favorable for the organism.
  • by gbutler69 (910166) on Sunday January 10, 2010 @10:59AM (#30714498) Homepage
    Possible maybe, but likely? There is probably a reason that DNA (and RNA) are DNA and RNA and not something else. It's the same reason by complex chemicals/life chemicals are mostly constructed around Carbon. Carbon has lots of free valences, which allow it to act like a universal lego-block. Other elements, just don't have as much flexibility. It's why it's entirely unlikely that you will ever see something that can be classified as life that isn't carbon-based. Other elements just can't be as flexible as Carbon.
  • Re:genetic material (Score:3, Informative)

    by Toonol (1057698) on Sunday January 10, 2010 @01:04PM (#30715198)
    You're correct. If they evolve, they HAVE genetic material; it's a bit of a tautology. They just don't necessarily have the same genetic material as we do. (Although our genetic material isn't 100% defined by our nuclear DNA; we have other inherited material, such as mitochondrial DNA, that is also part of our genetic makeup. In the wider, touchy-feely, view we have such things as memes and culture that might be considered 'genetic'.)
  • Re:Not Surprised. (Score:3, Informative)

    by goodmanj (234846) on Sunday January 10, 2010 @02:00PM (#30715576)

    Yes, the plants tend to be dry, oily, and highly flammable, with fire-resistant seeds. In the U.S., manzanita and similar plants are thought to do the same thing.

    However, this has no bearing on whether fire is alive. Symbiosis is not a requirement of life, but (I think) evolution by natural selection is. Fire doesn't contain information about itself -- its properties are only a function of its fuel. It's not like lighting paper with a match produces a different fire than lighting it with a candle. Fire doesn't undergo natural selection, except in the trivial sense that big fires are harder to put out.

  • Re:Matter. (Score:5, Informative)

    by Warbothong (905464) on Sunday January 10, 2010 @02:51PM (#30715934) Homepage

    Any matter has one mission and one mission only: to find greater order. If matter without DNA or any prior form of order couldn't achieve more order, then life would not exist. Things want to be able to interact with their environment more efficiently, and must evolve to do so.

    All things in the Universe try to minimise the amount of energy they have. In some special cases, like crystals for example, this means becoming more ordered: the energy of each atom/molecule depends on its distance from its neighbours, with each "preferring" the lowest energy distance. Getting as many neighbours as possible at this distance is effectively packing spheres with that distance as their radius, which turns out to be the most efficient with ordered arrangements like hexagonal close packing, so that's what's observed. In the general case, however, the amount of order goes down, see http://en.wikipedia.org/wiki/Entropy [wikipedia.org] . In fact, in every situation which becomes more ordered over time, Thermodynamics says that somewhere else there must be a system becoming even more disordered (as an example, if a system is minimising its energy by becoming ordered then it's exothermic: the energy its losing will come out as heat. This heat is itself disordered, and can disrupt the order of whatever it comes into contact with (which is why so many Physics experiments are done as close to zero Kelvin as possible). Also, the total energy such systems manage to lose is restricted by the fact that they are becoming more ordered, there is an "entropic cost" when becoming more ordered, which means that it requires energy to do and therefore the system must keep hold of that much energy to do it.

    For a simple example of how becoming more ordered takes energy, try stretching an elastic band. The polymers it's made of would, in a totally disordered system, take "random walks", which is very degenerate (there are LOADS of ways to randomly walk a certain distance starting at a point A and ending at a point B is the distance AB is much shorter than the distance you walk, ideally A and B are in the same place). That's the band's preferred state, and as such it isn't particularly long. By stretching it, the distance AB goes up, so there are fewer random walks of the same length which satisfy these new positions. In the extreme case the distance AB will be the same length as the walk, and there would only be one valid random walk between them (ie. going in a straight line). It takes energy to stretch the band because you're making it more ordered, which it doesn't want to be.

    If matter's mission is to find greater order then a stretched elastic band would never snap back ;)

  • by Bowling Moses (591924) on Sunday January 10, 2010 @02:58PM (#30715992) Journal
    Since evolution at the simplest level is change in allele frequency over time, let's take a look at your example using the very simplest case: fur color as a Mendelian trait: one gene two alleles. Let's also say that white fur is recessive (w) and the black fur is dominant (B), and there is no selective pressure other than your cat killing machine and no cats are born.

    Pre selection: 90 black cats (BB) and 9 white cats (ww)
    Post selection: 1 black cat (BB) and 9 white cats (ww)
    Pre selection, the black fur allele comprises 90.9% of the gene pool, white fur 9.1%.
    Post selection, the black fur allele comprises 10% of the gene pool, white fur 90%.

    So you clearly have a change in allele frequency, and therefore have clear-cut evolution. Let's change the experiment a little. Above it is assumed that all black cats have two black fur genes, which is going to show the biggest change in allele frequency possible under this experiment. Let's look at the other end, where all black cats are heterozygous for fur color.

    Pre selection: 90 black cats (Bw) and 9 white cats (ww)
    Post selection: 1 black cat (Bw) and 9 white cats (ww)
    Pre selection, the black fur allele comprises 45.5% of the gene pool, white fur 54.5%.
    Post selection, the black fur allele comprises 5% of the gene pool, white fur 95%.

    So again we clearly have a change in allele frequency and therefore clearly have evolution, no matter what the case for the original gene pool as we've covered both extremes.

    Now you're correct that in the absence of any other evolutionary mechanism the proportion of black cats will increase if the cats start mating. If we simply randomize the gametes (ignoring the impact of the small population size) from the first example where the black cats are homozygous for the trait we'll have 19% black cats in the next generation (1% BB, 18% Bw) and 81% white cats (ww). However we're at the Hardy-Weinberg equilibrium; in the absence of any evolutionary mechanisms the allele frequencies will not change any further, it's still 10% B and 90% w.

    It's not that selection != evolution. As demonstrated above it is possible that selection ==evolution. In a more realistic environment there are other factors at play but selection is still one of the most important evolutionary mechanisms.
  • Re:Not Surprised. (Score:3, Informative)

    by HiThere (15173) <charleshixsn AT earthlink DOT net> on Sunday January 10, 2010 @05:00PM (#30716936)

    You might look into the Southern Pine, then. Before people showed up and started "improving" things, the Southern Pine would shed lots of flamable needles that would build up, and cones that wouldn't release their seeds until AFTER being heated in a fire. Then they counted on a fire every few years, which would wipe out the competition.

    (Southern hear means the southern US. Places like Georgia.)

    P.S. Last I heard the Southern Pine was in trouble, but I haven't followed it. People tend to object to forest fires near where they live.

  • by Graff (532189) on Sunday January 10, 2010 @05:17PM (#30717082)

    Actually, if the black gene is dominant and you have a closed system that kills all black cats then you will end up with a population of only white cats.

    Dominant traits means that the dominant form of the gene masks the recessive trait. This means that if black is a dominant trait then a cat that has any amount of the black trait will be black. Thus your machine will kill every cat with that trait and there will be no cats with black traits to pass on to their offspring.

    Here's a diagram to show this:
    BB x WW = 100% BW
    BB x BB = 100% BB
    BW X BB = 50% BB, 50% BW
    BW X BW = 25% BB, 50% BW, 25% WW
    BW X WW = 50% BW, 50% WW
    WW x WW = 100% WW

    BB is pure black.
    BW is mixed types. If black is dominant the cat is a black color. If white is dominant the cat is a white color.
    WW is pure white.
    Percentages are approximate for a large sample size.

    When black is dominant any cat that is BB or BW is killed since both combinations result in a black cat, leaving only the cats that are WW and a white color. The black trait is removed from the population.

    If the black trait is recessive you will have the a different situation. The only cats that will be removed are the ones with BB so you'll have a lot of cats that are BW and every generation will still result in a noticeable percentage of BB (black) cats.

    Remember, evolution is not about completely removing traits that are selected against. Most times those traits are still around but because of selection pressure they tend to result in a lower level of fitness and therefore organisms exhibiting the trait are less successful and less common. If the selection pressure is removed you'll often see some of the suppressed traits exhibit themselves at higher rates in the population.

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