In medical terms, superfetation is defined as “the fertilization of a second ovum some time after the start of pregnancy, resulting in two foetuses of different maturity in the same uterus.” According to research into the phenomenon—which remains in some doubt due to a lack of understanding of the biological mechanism by which it is enabled—it results in the growth of fertilised eggs in the uterus of a hare alongside a developed foetus. Superfetation has been observed to occur naturally in some 13 per cent of hare pregnancies, and has been carried out artificially under laboratory conditions.
