You probably heard about last week’s Nature study on older dads and autism; it got a lot of attention. The basic findings were fascinating but, in my opinion, far less sensational than what most of the news articles would have us believe.

The researchers, led by Kári Stefánsson of deCODE Genetics in Iceland, showed that the average 20-year-old man passes on about 25 new single-letter DNA mutations to his child. (These kinds of mutations happen spontaneously in sperm cells, so they don’t affect the DNA in the father’s other cells.) With each passing year of age, the man’s sperm acquires two more mutations. This makes sense, biologically. Sperm Primordial sperm cells divide over and over throughout a man’s life. To use an over-used metaphor: