The BBC has an article on the recent direct measurement of human mutation rates, and while it’s not a bad article, it does seem to express the view that the result is something novel. It’s not; it’s a confirmation of a standard measure that scientists have known about for a long, long time. We have estimated the number of novel mutations in newborn human individuals to be somewhere between a hundred and a few hundred (best estimates were on the order of 150) based on a couple of facts.
We’ve had measurements of the fidelity of the enzymes that catalyze replication, and since we know both the per nucleotide rate and the number of nucleotides, it’s straightforward to calculate the average number of errors per replication event. We’ve also had estimates from the measured frequency of spontaneous mutations in human disease genes that have given answers in the same ballpark. The only thing new in this recent study is that they sequenced the Y chromosomes of a group of related men and directly tallied up the new mutations, confirming that the previous calculations were roughly correct.
Like I say, it’s not a bad article, but if you really want the best summary of the work, you should be reading Sandwalk.
It’s useful information for the next time you’re in a debate with a creationist, too. They often assert that all mutations are harmful, but clearly, they can’t be: they’re almost entirely neutral. That creationist is carrying over a hundred new mutations that his parents lacked, and his children will each have over a hundred more, and his grandchildren a hundred yet again. What we have going on is a great churn of frequent change, just change, not a pattern of directional variation that either degrades or elevates us.