Weaknesses of Evolution – Part 10 – Most Mutations are Harmful
Bull cookies. Creationists have been claiming this for decades. Very often, they will also talk about how mutations damage genes and don’t help, therefore over long periods of time genomes will ‘collapse’ under the weight of their harmful mutations.
Most all mutations are detrimental, a few are neutral, and extremely few if any are clearly beneficial.
The sad part is that this simply isn’t true and it has been shown to be false for a long, long time.
Most mutations are neutral and have no effect on the gene or resulting protein. A study published in 2000 shows that humans average 3 deleterious mutations out of 175 mutations per generation. A more recent study shows that the beneficial mutation rate in bacteria is very high.
Given the estimates for the overall mutation rate in E. coli (30) and its genomic deleterious mutation rate (1), our estimate of Ua implies that 1 in 150 newly arising mutations is beneficial and that 1 in 10 fitness-affecting mutations increases the fitness of the individual carrying it.
If you allow a bit of cross-species comparison, then 3 deleterious mutations out of 175 and 1 beneficial mutation in 150, that’s about 4 non-neutral mutations out of every 150-175 mutations. The vast majority of mutations have no effect.
Another item that absolutely must be considered is that detrimental mutations can be potentiating mutations. That is, the change caused by one mutation reduces efficiency of some protein, but that mutation, when combined with another mutation results in a huge improvement in efficiency.
This is my absolutely favorite evolution study. It’s so simple and so effective at showing exactly what evolution can do.
In this study, an RNA enzyme was placed in a situation where it was imperfectly copied. By reducing the amount of substrate available to the enzyme in each iteration of the experiment, the researchers could select for improved function in the enzyme.
The final enzyme was genetically analyzed and found to have 11 mutations. The final enzyme had a 90-fold improvement in enzyme activity. This improvement occurred in 70 hours.
What’s really interesting is that there were four main mutational groups (M1, M2, M3, M4) identified in the final enzyme. Using some cool tools, the researchers built enzymes with each mutation by itself. The M4 mutation, by itself, resulted in a 2-fold decrease in enzyme efficiency. But in the presence of any of the other three mutation groups, M4 increased the efficiency of the other mutations.
That is how even a harmful mutation can result in a greater overall benefit. Even if a mutation is harmful, if it isn’t harmful enough to kill the organism, then it could very well be the change needed for future organisms to have greater benefits.
If you are interested in how mutations can have no effect, then read on.
There are several types of mutations. We’re only going to talk about gene mutations here. Chromosomal mutations are whole ‘nother animal, as my grandad would say. One kind of gene mutation is called a ‘frame shift’. This is caused by an insertion or a deletion in the gene. These types of mutations are almost universally bad because the render everything after that point wrong.
Think about this sentence.
The red cat ran and sat
Now we insert a letter.
The rea dca tra nan dsa t
Yep, totally unintelligible. Now, it can happen that a frameshoft results in a completely new protein that does something cool, but the odds are not favorable.
Another kind of mutation is the ‘point mutation’. In this case, a single nucleotide changes from one letter (A, T, G, or C) to another one. These mutations are mostly neutral for two reasons. The first is because of how genes are translated into proteins. Each three nucleotides in a gene code for a particular amino acid. But the code has a lot of redundancy in it. (This website explains the process of transcription and translation.)
For example, the RNA nucleotide sequence UCU codes for the amino acid serine. But so does UCC, UCA, UCG, AGU, and AGC. Any mutation that hits the last letter of that codon will have no effect. Because the last letter doesn’t matter. UCx always codes for serine (where x is any nucleotide).
Eight of the twenty amino acids in the human system have the same setup. It doesn’t matter what the last letter is. Serine, Arginine, and Leucine have six coding combinations. That’s more than half of the amino acids.
Except for methionine and tryptophan, the others have at least two combinations that code for them. Just mathematically speaking, there are a large number of mutations that cannot have any effect on the protein at all.
The second way that a mutation may have no effect is that in some areas of the protein, the actual amino acid present doesn’t really matter. Proteins may be huge molecules, but only a very small section is what is called the ‘active site’, where the protein actually does whatever it’s supposed to do. The rest is just structure.
In many cases, the actual amino acids present in the structure don’t matter as long as they have the same characteristics. Some amino acids are attracted to water, some are repelled by water. There are plenty of places in a protein molecule that the actual amino acid used doesn’t matter, as long it is repelled by water. That’s just to keep the shape correct.
If you’re building a house, then the main support beam in the roof can be wood, steel, even concrete… as long as it’s the right length and can support the structure.
I would like to add one more major point about why mutations can be neutral. Even mutations that cause a massive frameshift in a vitally important protein can be neutral.
Wow, that’s a big claim. Can I back that up? Well duh…
It’s actually very simple. Sexual organisms have TWO copies of every gene (except for some genes on the male sex chromosome). One of the copies of a gene can be massively corrupted, but just like having two hard drives with the same information, our bodies can just ignore the corrupted information. We still have a good copy of the gene.
In many cases, chromosome mutations have resulted in having many, many copies of the same gene. So what if a mutation happens in a copy? In fact, that’s how a lot of major evolutionary events are proposed to have happened.
The original gene can keep on doing what it’s supposed to, while the copy is free to be mutated and changed into something very similar, but with a different function.
Here we see that the creationists are simply wrong. I feel like I’m repeating myself, but it’s because creationists keep making mistakes. They don’t have the foggiest notion of what is actually going on in biology, evolution, or science.