Unlike rugged sperm and hardy embryos, human eggs and the ovaries that contain them have proved extremely difficult to freeze and resurrect.

ECONOMIST: Frozen ovaries could help women to stay fertile

With human cloning technology just around the corner and enough frozen sperm in the world to already populate many generations, perhaps we should perform a cost-benefit analysis.

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But thanks to new research published in the journal Human Reproduction, guys with fertility on their minds can add sperm size to their docket of worries.

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South Korea's researchers have taken egg cells from volunteer women, removed the nuclei from those cells (which contain only half of the genetic complement required to make a human being, since the other half is provided by the sperm), and replaced each nucleus with one taken from one of the volunteer's body cells (which contains a full genetic complement).

ECONOMIST: An embryonic development