"If you want healthy offspring, don't leave fatherhood too late".
Mice sperm frozen in the early 1970s and periodically thawed still produce healthy offspring.
Both procedures have been tested in animals and resulted in healthy offspring.
"It is clearly important to make sure that any sperm produced are safe and give rise to healthy offspring when used, and that they in turn have healthy offspring.
"We don't really know what the complete effects are of men's age on their ability to produce viable, healthy offspring".
Tillicum sired some 13 calves, and has lived with females rearing healthy offspring for decades.
Such women as can have healthy offspring become "high-prize objects – because to not have a fucking tumour on you is a fucking miracle.
For example, a woman who rears six healthy offspring has greater fitness than one who rears just two.
Even if it does not die, the chance of it giving birth to healthy offspring is low.
Where disease is rife, this seemed to imply, giving birth to healthy offspring trumps having a man stick around long enough to help care for it.
Once taken off the drug, the males reverted to normal sperm counts, sufffered no permanent damage to their reproductive organs, and sired typical numbers of healthy offspring.
