Evolution Works

I've been gone partially due to technical issues. OpenOffice is great, but it turns out there are some reasons to actually go ahead and buy the real thing. Anyway, onward!

I was recently told that evolution couldn't possibly work because it would take billions of mutations in every species to get the number of mutations needed to drive evolution. There is a lot wrong with this statement, the first of which is that mutation rate is only a small part of the genetic variation that drives evolution. This person, like so many that argue against evolution, has no understanding of how evolution works, nor of the mechanisms genetic variation.

I won't go into a long defense of evolution here, but I thought I would address his statement of the billions of mutations that we don't see, according to him. How many mutations can we really expect? The answer is vastly greater than most people realize.

DNA is well protected by several molecular mechanisms designed to ensure an accurate duplication. But mistakes, or mutations, will occur no matterhow good the quality control process. Mutation rate varies tremendously depending on the conditions, but in humans, the average mutation rate is 2.5 x 10^-8 (0.000000025) per nucleotide (http://www.genetics.org/cgi/content/full/156/1/297). This means that there is one mutation for every 250,000,000 nucleotides. Sounds pretty good doesn't it?

The problem here is that there are 3 billion basepairs in the human genome, or 6 billion nucleotides (http://www.ornl.gov/sci/techresources/HumanheyGenome/faq/faqs1.shtml). This means there are 150 mistakes each time it is replicated (the paper cited above states there 175 errors per doubling, but we will go with these conservative numbers).

Ok, so nowhere near the billions we need, right? But consider just how many times we need to copy that DNA every time we try to have sex. I am going to leave women out of this because the number of mutations women contribute is so small compared to men that it is insignificant. You'll see why in just a second, but it is safe to say that the vast majority of mutation driven evolution is driven by men.

The number of sperm in one ejaculation, even if we use the lower than commonly reported values here (http://www.ispub.com/ostia/index.php?xmlFilePath=journals/iju/vol2n1/sperm.xml), is about 50 million sperm/ml and there are 2-6 ml/ejaculate. So we'll be conservative again and use 3 ml, giving 150 million sperm/ejaculate (also note that the paper cited above on mutation rate says that males have 4 times the mutation rate of females, but we will go with the average stated). One should also keep in mind that most places report 250-300 million sperm in the average ejaculate.

So, if there are 150 mistakes in every sperm, there are 150 x 150 million = 22500 million, or 22.5 billion mistakes in every ejaculation. So every time every single male ejaculates, he is supplying more than enough mutations to drive evolution for the whole human race according to the creationist that was pontificating to me.

But wait! There's more! There are over approximately 2.23 billion males between 15-64 on the planet right now (https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html). So, assuming that we count one ejaculation for each man, that is 5x 10^19 mutations.

Estimates vary as to how many times the average man ejaculates in his life, but most estimates are between 5-8,000 times. But let's only count ones that are in the age range that most men are fathering babies and only count the number of times that the man is actually having sex, so those sperm have a chance of making a baby. No matter where you go, every survey and study lists the average person as having sex at least 100 times a year. But let's assume that is way more than the "average" and let's only count, say, 200 times in their entire life. That means that there are 10^21 mutations in every generation of human males.

That number puts the national debt to shame. So it is clear that evolution has plenty of material to work with. This is precisely why the problem is NOT getting enough variation. The problem is why don't we evolve faster? Fortunately, modern evolutionary theory has answers for that too in the form of stabilizing selection and numerous other methods to keep evolution from going crazy.

So be prepared, the next time any of you tell me that evolution can't work because there aren't enough mutations, I will laugh in your face and mock you mercilessly.