Infections, prions and evolution
New reports, same old issues—but there’s a ‘different twist’
Published: 19 January 2010(GMT+10)
Some recent widely distributed articles have caused a flurry of queries about the whole issue of how infectious disease relates to the issue of creation-evolution.
The first is a somewhat heart-rending report of the first appearance in the United States of a strain of tuberculosis (TB) highly resistant to multiple antibiotics.1 It occurred in a 19-year-old Peruvian visiting to study English, only to be fighting for his life. Such an extreme case of resistance is very rare, with only a handful of cases reported in the whole world to date. But multiple drug resistance in TB in general is on the increase, and is causing serious concern to health authorities.
Only 1 in 10 people who carry this insidious disease get an active infection, but that has to be seen coupled with the fact that over 2 billion people, around a third of the world’s population, is infected with the TB bacillus. Currently, well over 1½ million people die from TB each year, in a rising toll that is concentrated mostly in poverty-stricken nations. Of these deaths, a very large number occur because the immune system was compromised by AIDS, another scourge of the poor.
Whenever one hears of bacteria or viruses ‘evolving’ resistance to drugs, some anti-Christian website somewhere will use it to show how this is proof of goo-to-you evolution. But no one denies that natural selection or mutations are real, or that creatures can adapt via natural selection to new environments. For a clear discussion, see our articles Muddy waters: clarifying the confusion about natural selection, and The evolution train’s a-comin’ (sorry, a-goin’—in the wrong direction), and their associated links.
So-called ‘mad cow disease’ is just one example of the syndromes that can be caused by prions.
A population of bacteria adapting to an environment containing something that would normally kill them is, by itself, something that is no different from a population of dogs adapting to cold winters through having longer hair on average than their ancestors. In both instances, the issue is, does this give evidence of the sorts of changes required to transform microbes into people, if extrapolated over millions of years? The answer is clearly a resounding ‘no’ when understood properly, as shown in the abovementioned articles.
What about prions?
However, as far as infectious agents causing disease is concerned, there is now a new kid on the block, and which is also supposed to involve ‘evolution in action’. There are infectious diseases which are not caused by either bacteria or viruses, but by a newly discovered type of infective agent called a prion. These diseases, which were once shrouded in mystery as to their causes, include:
- bovine spongiform encephalitis (BSE or ‘mad cow disease’);
- Creutzfeldt-Jakob syndrome (a similar brain affliction to BSE, but in humans);
- scrapie (affecting sheep); and
- kuru (a brain disease of humans which was at one stage likely spread by the ritual eating of human brains in certain cultures in Papua New Guinea).2
As far as infectious agents causing disease is concerned, there is now a new kid on the block.
The discovery of prion infection has an interesting history, though beyond the scope of this article. Imagine tracking down the clues pointing to an infectious agent (which is something that replicates itself), only to find that the infectious material you think you have contains neither DNA or RNA! All bacteria use these code-bearing molecules, as part of programmed machinery with which a bacterium makes copies of itself.. Viruses do not have this machinery, therefore they are not really living,3 as they need to hijack the machinery of a living cell to reproduce. They insert their own ‘program’ to control the cell’s machinery. But in all known viruses, this program is in the form of RNA or DNA, part of the normal ‘language of life’. Prions have neither machinery to replicate themselves, nor code to hijack the machinery of the cell.
So what is a prion?
That something that replicates and can vary is capable of differential replication adds nothing at all new to the discussion regarding evolution.
The word ‘prion’ is a combination of ‘protein’ and ‘infection’. A prion is essentially an abnormally folded protein. The many sophisticated molecular machines in our bodies are proteins—for example, insulin, RNA polymerase, hemoglobin, and more, maybe 100,000 or more different ones. (These all perform machine-like functions in the body, but there are also structural proteins like collagen.) In the enormously complex processes in the cell, chains of amino acids are put together in a specific sequence to become proteins—like letters of the alphabet put together in a sentence, a different sequence gives a different ‘meaning’, i.e. a different protein.4 This is all under the direction of the programmed code written on DNA. Once the amino acid chain emerges in the correct sequence, the properties and functions of the protein that results come from the three-dimensional shape it then adopts by folding. This is a natural result of the various attractive and repulsive forces on the surface of its molecules.5 However, left to itself, this process would often take far too long, so it is helped by even further sophisticated machines, known as chaperones (also made of proteins).
A protein with a ‘different twist’
Sometimes, in this folding process, things get messed up, and a protein is abnormally folded. One way of understanding it might be that it is like having a mutated protein, rather than a mutated gene, which is what mutations normally are. I.e. it is a defect in the end product, rather than a defect in the code. This distorted shape means it is a defective protein, one that cannot perform its normal function properly. However, normally such defective proteins do not cause a problem, because they are ‘one-offs’. A defective gene, being a defective set of instructions, will cause the cell’s machinery to keep making more and more of a defective protein. It’s like the blueprint in the Daimler-Benz factory being messed up so that a whole succession of junkheaps emerge instead of shiny models of Mercedes. But to have the occasional mistake come off a protein assembly line is different, and does not generally cause big problems, because the machinery is still properly programmed, so that most of the protein molecules come out just fine.
A prion is a mutated protein, rather than a mutated gene—a defect in the end product, rather than a defect in the code.
However, very rarely one such mis-folded protein can just happen to have the physico-chemical properties that enable it to induce neighbouring proteins of the same type to become just as misshapen as it is. (Remember that proteins have not just specific shapes, but a specific pattern of attractive and repulsive forces on their complex surfaces.) Imagine a particular protein that, when folded properly, we’ll call X. Now imagine that there is a distorted, mis-folded version of that same protein, call it X^, which happens to have these ‘prion’ properties. That means that if some material containing X^ is introduced into a part of the body where there is a concentration of molecules of X, performing some useful function, say, then it may only take one molecule of X^ to distort a neighbouring X molecule into refolding into an X^. In that way, one X^ has become two—even though nothing new was ‘manufactured’. It can later do the same to another, and each of its ‘offspring’ can do the same in turn. In this way, the molecule can be said to ‘replicate’ itself, even though there are no actual manufacturing functions going on, and it explains why prions do not need either machinery or coded instructions like DNA or RNA to make copies of themselves.
How do prions cause problems?
The prion version of the protein will then keep building up in this way, which can be very slow. Prions seem to do their damage not so much by depriving the tissue concerned of X (which can be compensated for by making more X) but by the accumulation of the X^.
To undergo what are called the Darwinian processes of natural selection and mutation, any entity, biological or otherwise, only needs to be able to
- have the possibility of having variations in the outcome of that process of replication, so that the selection process has different options from which to ‘choose’.
Certain groups in Papua New Guinea were believed to be vulnerable to the brain disease kuru, perhaps because the ritualistic eating of human remains transmitted the prion responsible. (For illustration only)
This is a matter of simple logic, requiring no experimental proof, in one sense.
We’ve already seen that prions can replicate. And factor (b) above applies to them as well—the ‘replication’ process is not perfect, so there can be slightly different forms of the X^; let’s say X^^ as well as X^. If the X^^ is, in a particular environment, better able to make copies of itself than the X^, it should be favoured by selection. So it’s no surprise at all that a recent paper has announced that prions in a laboratory situation have been shown to be able to undergo these ‘Darwinian’ processes, i.e. differential replication where one type is more readily able to replicate than another.6,7
But it’s already been overwhelmingly shown that demonstrating such Darwinian processes does not demonstrate the Darwinian conclusion that all life descended from a common ancestor. Natural selection of natural variation was observed, and written about, by a creationist, before Darwin. It is the mechanism that Darwin proposed for his ‘evolution’, it is not evolution itself. Observing such a phenomenon (already discussed in depth, and accepted as fact, by informed creationists for decades) is not the same as observing evolution, and saying that it is begs the question of whether the mechanism is capable of the massive task assigned to it by evolutionists. The evidence strongly indicates that it is not.
This totally unsurprising result (that something that replicates and can vary is capable of differential replication) adds nothing at all new to the discussion regarding evolution. It shows how slightly different forms of the same prion are more likely to accumulate in some body environments than in others. In fact, it should, if anything, be far less interesting for evolutionists than bacterial mutation/selection, since microbes are living things, and can at least be claimed by them to have been our ancestors. Proteins, on the other hand, don’t arise without the machinery of a living cell, so can hardly have been the ancestors of life.
- First case of highly drug-resistant TB found in US, news.yahoo.com, 27 December 2009. Return to text.
- There was an outbreak of kuru in Papua New Guinea in the mid-20th Century. It seems closely related to Creutzfeldt-Jakob disease. Return to text.
- They certainly can’t qualify as a ‘simpler and earlier’ form of life to put at the base of the evolutionist’s ‘tree’. This is because you have to have the machinery of a living thing present first, before a virus can replicate itself. Return to text.
- There are 20 letters in the amino acid ‘alphabet’, i.e. only 20 amino acids make up the vast number of different proteins. Return to text.
- The idea of molecules folding themselves is one of those ‘oversimplifications of necessity’. Factors such as solvent/solute concentrations, temperature and more come into play. Return to text.
- Li, J., Browning, S., Mahal, S.P., Oelschlegel, A.M. and Weissmann, C., Darwinian Evolution of Prions in Cell Culture, sciencemag.org, 31 December 2009. Return to text.
- Of course, prion disease caused by such a more successful form of prion protein can not be inherited, as it is not a genetic change that can be transmitted via sexual reproduction. Prion diseases are acquired by ingesting material already infected with one of these distorted proteins, which then distorts the normal proteins of that type which one is already making. Return to text.
I hate to be pedantic, and not that it really matters, but I noticed the statement, "The word ‘prion’ is a combination of ‘protein’ and ‘infection’." It is actually (PR)oteinaceous (I)nfectious (ON)ly that makes the prion acronym.
Hi, Ashley. I don't want to be kneejerk defensive of my own writing, and generally I have no problem making a correction. And several sites agree with you, even though the phrase seems grammatically incorrect. But others don't. E.g. Wikipedia (for what that's worth) agrees with what I was taught in medical school, which is what this article reflects, namely that it is derived from protein and infection. It seems likely definitive, however, to find out what the man who invented the term says it was supposed to mean. That was the the guy who won the Nobel Prize for it, Stanley B. Prusiner, and in his autobiography on the Nobel site, he writes as follows (bold emphases added):
"Publication of this manuscript, in which I introduced the term "prion", set off a firestorm. Virologists were generally incredulous and some investigators working on scrapie and CJD were irate. The term prion derived from protein and infectious provided a challenge to find the nucleic acid of the putative "scrapie virus."
Having these comments of ours below the article will help readers who might otherwise be confused by this apparent range of possibilities, so thank you.