Children are more likely to inherit "new" genetic mutations if they have older parents, a study has shown.
Fathers who have children late in life are most at risk of passing on the changes, which can trigger rare diseases, in their sperm.
Scientists searched for so-called "de novo" mutations (DNMs) in the DNA of 14,688 Icelanders who had their whole genetic code sequenced.
DNMs are gene alterations that appear for the first time in eggs or sperm rather than being carried for generations.
They are key drivers of evolution in both animals and plants, but can be harmful.
The Icelandic study identified a total of 108,778 high quality DNMs with an average of 70.3 per family.
With each year of increasing age, the number of de novo mutations inherited from mothers increased by 0.37 - a quarter of the 1.51 per year rate from fathers.
Dr Kari Stefansson, chief executive of the Icelandic genetics company deCODE which carried out the analysis, said: "This is an important new chapter in our ongoing work to understand the mechanisms driving genomic diversity and through that the evolution of our species.
"De novo or new mutations provide an important part of the substrate for evolution, launching a constant flow of new versions of the human genome into the environment.
"However, they are also believed to be responsible for the majority of cases of rare diseases of childhood.
"Providing a comprehensive catalogue of such mutations from across an entire population is therefore not just scientifically interesting but also an important contribution to improving rare disease diagnostics."
The findings are published in the journal Nature.
Allan Pacey, Professor of Andrology at the University of Sheffield, said:
"Put simply, the genetic quality of sperm from younger men (in terms of de novo mutations) is generally much better than that of older men."
