Research into the genomes of thousands of Icelandic parents and children has found that older fathers pass on more genetic mutations to their offspring than older mothers do.
Whilst women are born with all their eggs, men continually produce sperm, even as they age. This means that every cell division is at risk of creating a new genetic mutation.
Not all mutations are harmful, but there might be the occasional one that is. The study found that 80% of new mutations come from the father and that this increases in line with age.