Genetic entropy and simple organisms
If genetic entropy is true, why do bacteria still exist?
Published: 25 October 2012 (GMT+10)
Genetic entropy (GE) is eroding the genomes of all living organisms because mutations are inherited from one generation to the next. Many people wonder why, if GE is real, are bacteria still alive today? There are multiple reasons for this, including the fact that their genomes are simpler, they have high population sizes and short generation times, and they have lower overall mutation rates. This combination makes them the most resistant to extinction. Of all the forms of life on Earth, bacteria are the best candidates for surviving the effects of GE over the long term. This does not mean they can do so forever, but it explains why they are still around today.
What is genetic entropy?
After the landmark publication of Genetic Entropy and the Mystery of the Genome by Cornell University Professor Dr John Sanford, we have often been asked to supply further details of this major challenge to evolutionary theory. The central part of Sanford’s argument is that mutations (spelling mistakes in DNA) are accumulating so quickly in some creatures (particularly people) that natural selection cannot stop the functional degradation of the genome—let alone drive an evolutionary process that can turn apes into people.
A simple analogy would be rust slowly spreading throughout a car over time. Each little bit of rust (akin to a single mutation in an organism) is almost inconsequential on its own, but if the rusting process cannot be stopped it will eventually destroy the car. A more accurate analogy would be to imagine a copy of Encyclopedia Britannica on a computer that has a virus that randomly swaps, switches, deletes, and inverts letters over time. For a while there would be almost no noticeable effect, but over time the text would contain more and more errors, until it became meaningless gibberish. In biological terms, ‘mutational meltdown’ would have occurred.
When living things reproduce, they make a copy of their DNA and pass this to their progeny. From time to time, mistakes occur, and the next generation does not have a perfect copy of the original DNA. These copying errors are known as mutations. Most people think that ‘natural selection’ can dispose of harmful mutations by eliminating individuals that carry them. But ‘natural selection’ properly defined simply means ‘differential reproduction’, meaning some organisms leave more progeny than others based on the mutations they carry and the environment in which they live. Moreover, reproductive success is only affected by mutations that have a significant effect. Unless mutations cause a noticeable reduction in reproductive rates, the organisms that carry them will be just as successful in leaving offspring as all the others. In other words, if the mutations aren’t ‘bad’ enough, selection can’t ‘see’ them, cannot eliminate them, and the mutations will accumulate. The result is ‘genetic entropy’. Each new generation carries all the mutations of previous generations plus their own. Over time, all these very slightly harmful mutations build up to a point that, in combination, they start to have serious effects on reproductive fitness. The downward spiral becomes unstoppable, because every member of the population has the same problem: natural selection can’t choose between ‘fit’ and ‘less fit’ individuals if every member of the population is, more or less, equally mutated. The population descends into sickness and finally becomes extinct. There’s simply no way to stop it.
Dr Sanford argues that humans could not possibly have been around for tens of thousands of years (let alone millions, or billions if one considers our supposed evolutionary animal ancestors) because, at the current rate of mutation and the number of generations that would have occurred, we should have already become extinct.
Genetic entropy in bacteria
From time to time, we are asked by honest people seeking a better understanding, as well as hostile people trying to challenge us, to explain why, if genetic entropy (GE) is true, do bacteria still exist? After all, bacteria have extremely short generation times. Some bacteria can reproduce every 20 minutes, so would be gaining far more mutations in a day than humans would in a hundred years. And bacteria are much simpler organisms, so it should take less time to break down their genetic instruction set compared to humans. Why, then, did they not go extinct long ago?
There are several ways to answer this. First, the idea of GE was developed by population geneticists working on higher genomes (i.e. genomes of the more complex organisms with longer generation times). The big puzzle is why species like humans have not gone extinct if we have been around for tens of thousands of years as evolutionists maintain.1 In a complex organism, a high mutation rate combined with a low reproduction rate makes it very difficult for ‘natural selection’ to remove deleterious mutations from the population. Thus, higher mammals like people and elephants are not good candidates for long-term survival because mutations accumulate from one generation to the next. For eukaryotic organisms (everything more complex than bacteria), the complexity of the genome makes the ‘mutation target’ quite large—in these more-complicated systems, there are more things that can go wrong, i.e. more machinery that can be broken.2
On the other hand, changes to simpler genomes will often have more of a profound effect. Changing one letter out of the three billion letters in the human genome is not likely to create a radical difference. But the genome of the bacterium E. coli, for example, is about 1,000 times smaller than that of humans; bacteria are more specialized and perform fewer functions. Any letter change is more likely to do something that natural selection can ‘see’. That is, it is more likely that a small change will produce a large enough effect that it will make a difference in the number of individuals carrying that trait generations later.
It’s important to note that there are multiple things going on at once. We have to consider a combination of factors in order to understand why bacteria are still with us today. Let’s use an illustration. Bacteria are like bicycles. People are like sports cars. One can make a number of modifications to both without breaking them, but there are fewer parts in a bicycle, so any given modification is more likely to produce a non-working bicycle. They need two wheels, a handle bar, a frame, a chain, and at least two gear sprockets. There is very little you can remove from them or break before they can’t be used. Cars, on the other hand, don’t need a roof, windshield, or headlights. There are a lot more modifications you can make to a car and still drive it around. You may not get to work on time, because it does not operate at full potential, but the car can still be driven.
But why, if mutation is more likely to kill or harm a bacterial cell, do they still exist?
First, bacteria do suffer from GE. In fact, and perhaps counter intuitively, this is what allows them to specialize quickly.3 Many have become resistant to antibiotics4 and at least one has managed to pick up the ability to digest non-natural, man-made nylon.5 This is only possible with much ‘genetic experimentation’, mostly through mutation, but sometimes through the wholesale swapping of working genes from one species to another. Many mutations plus many generations gives lots of time for lots of genetic experiments. In fact, we have many examples, including those just mentioned, where breaking a perfectly good working system allows a new trait to develop.6 Recently, it was discovered that oceanic bacteria tend to lose genes for vital functions as long as other species of bacteria are living in the area. Here we have an example of multiple species losing working genes but surviving because they are supported by the metabolic excretions of other species.7 Since the changes are one-way and downhill, this is another form of GE.
Lower mutation rates
Another reason why bacteria still exist is that they have a lower overall mutation rate. The mutation rate in E. coli has been estimated to be about 1 in 10–10, or one mutation for every 10 billion letters copied.8 Compare this to the size of the E. coli genome (about 4.2 million letters) and you can see that mutation is rare per cell. Now compare this statistic to the estimated rate of mutation per newborn human baby (about 100 new mutations per child2) and one can begin to see the problem. Thus, there are nearly always non-mutated bacteria around, enabling the species to survive. However, there are also always mutated bacteria present, so the species are able to explore new ecological niches (although most known examples have arisen at the expense of long-term survival).
Incredible growth potential
Bacteria have an amazing growth rate. The entire world population of a species like E. coli turns over very fast (perhaps once per hour). Trillions upon trillions of these cells die for many different reasons each and every hour. Thus, this may be a system where natural selection can actually halt the inevitable decay. Why? Because any mutation that confers even a small disadvantage (and most do) can be removed through differential reproduction, given enough time. (Time in this case is measured in generations.)
Bacteria can replace themselves after a population crash in a very short period of time. This is a key reason they do not suffer extinction. Thus, when exposed to antibiotics, for example, the few resistant cells within the population can grow into a large replacement population in short order, even though 99.99% of the original bacteria may have died. If the antibiotic is removed, the population can turn over again, with the non-resistant ones replacing the resistant ones (because antibiotic resistance is usually associated with impaired growth, so the originals grow faster and would dominate the population in a few generations). Humans cannot do this. It would take thousands of years to replace the current population of 7 billion people, and the inbreeding that would occur when the few survivors were forced to marry close relations might drive us to extinction anyway.9
Bacteria vastly outnumber people
Population size is another consideration. There are many more bacteria than people. But since bacterial population sizes are relatively constant, there isn’t room for more, and competition is extreme. Most lineages die out in the long run. In large populations, with lots of competition, mutations can be purged more efficiently through differential reproduction. Any cell with a slight advantage over another is more likely, over generations, to persist.
It is quite feasible that many bacterial species undergo significant periods of dormancy. Bacteria coming out of dormancy would serve as a continual source of older, less mutated versions and would help to prevent GE over the long term.
Mutations can’t hide in prokaryotic genomes
Eukaryotes, such as humans, inherit two copies of each chromosome—one from each parent.10 Thus, any mutation on one human chromosome is often masked by the good copy on the other chromosome. This interferes with differential reproduction based on mutational differences (e.g. ‘natural selection’) and increases the mutation burden of our species. This is not true for bacteria, which reproduce asexually and inherit their DNA from only one parent.
What about other fast-reproducing organisms?
One might reply, “But mice have genomes about the size of the human genome and have much shorter generation times. Why do we not see evidence of GE in them?” Actually, we do. The common house mouse, Mus musculus, has much more genetic diversity than people do, including a huge range of chromosomal differences from one sub-population to the next. They are certainly experiencing GE. On the other hand, they seem to have a lower per-generation mutation rate. Couple that with a much shorter generation time and a much greater population size, and, like bacteria, there is ample opportunity to remove bad mutations from the population. Long-lived species with low population growth rates (e.g. humans) are the most threatened, but the others are not immune.
There are attempted evolutionary counter arguments to the basic GE hypothesis. They are weak, but it is not the purpose of this article to give an all-comprehensive defense of the theory. It is sufficient to say, however, that bacteria, of all the life forms on Earth, are the best candidates for surviving the effects of GE over the long term. Their simpler genomes, high population sizes, short generation times, and lower overall mutation rates combine to make them the most resistant to extinction. However, this does not mean they can do this forever and, in the end, they will be burned up along with everything else when Christ returns.
- Kondrashov, A., Contamination of the genome by very slightly deleterious mutations: why have we not died 100 times over?, Journal of Theoretical Biology 175:583–594, 1995. Return to text.
- Lynch, M., Rate, molecular spectrum, and consequences of human mutation, Proceedings of the National Academy of Sciences (USA) 107(3):961–968, 2010. Return to text.
- C.f., Sniegowski, P.D., Gerrish, P.J., Lenski, R.E., Evolution of high mutation rates in experimental populations of E. coli, Nature 387:703–704. Return to text.
- Bergman, J., Does the acquisition of antibiotic and pesticide resistance provide evidence for evolution?, Journal of Creation 17(1):26–32, 2003. Return to text.
- Batten, D., The adaptation of bacteria to feeding on nylon waste, Journal of Creation 17(3):3–5, 2003; creation.com/the-adaptation-of-bacteria-to-feeding-on-nylon-waste. See also the comment on “nylonase” below this article: creation.com/question-evolution. Return to text.
- See our Q&A pages on mutations and natural selection. Return to text.
- Morris, J.J., Lenski, R.E., Zinser, E.R., The Black Queen Hypothesis: evolution of dependencies through adaptive gene loss, mBio 3(2):e00036–12, 2012. Return to text.
- Tago, Y., Imai, M., Ihara, M., Atofuji, H., Nagata, Y., and Yamamoto, K., Escherichia coli mutator Delta polA is defective in base mismatch correction: The nature of in vivo DNA replication errors, Journal of Molecular Biology 351:299–308, 2005. Return to text.
- This would not have been a problem for the human population immediately after Noah’s Flood. Being only 10 generations or so removed from Adam, they would not yet have picked up all the deleterious mutations we carry today. Return to text.
- Exceptions include red blood cells, which don’t have nuclei, and liver cells, which often have extra copies of many chromosomes. Return to text.