A German study involving 1.4 million individuals  concludes that older fathers are more likely to have less fertile children. This phenomenon is allegedly due to the quality of the sperm, which decreases with age. Scientists at Georg August University in Göttingen explain that sperm DNA of older fathers carries mutations which affect the child’s fertility in later life (see “Shouldn’t medically assisted procreation requests from older couples be discouraged”?).
This effect has not been seen in older mothers. Whereas men produce sperm from puberty onwards, women are born with a specific supply of eggs.
 Sweden, Canada and Germany – three populations from different eras were analysed to ensure that the effects were not due to current chemical products.