The embryos of a male and female twin can sometimes fuse into a single fetus with both male and female sexual organs. Now an imaginative biologist has figured out how this could lead to conceiving a son without a father.
Any organism that undergoes this fusion process is known as a chimera. Chimeras can be plants, animals, or humans, and the pair of fused organisms can either have the same or different genders. It's when chimeras formed from twins of different genders that we can observe otherwise impossible phenomena, including organisms gaining the ability to self-fertilize one of their own eggs. This has been seen in plants, fish, and rabbits. It's also perfectly possible for chimeras to lead normal sexual lives - human chimeras of multiple genders have both become pregnant and fathered children.
But now M.K. Irmak of Turkey's Gulhane Military Medical Academy has figured out how a human chimera reared as a female could become pregnant with a son without ever having sex with a man. The dependably awesome NCBI ROFL has his rather involved scenario:
"She is a chimera of 46,XX/46,XY type resulting from the fusion of two zygotes of different sex types and she develops both ovary and testis in her body. Since XX cells tend to gather on the left side while XY cells on the right, she develops an ovary on the left side with a oviduct and a testis on the right side located in an ovarian position with no duct...Both gonads are functional and produce spermatozoa and oocyte respectively after puberty. At the time of ovulation, estrogens increase the motility of the oviduct on the left side which results in a negative pressure in the tube and oocyte and sperms are picked-up into the tube with the help of this vacuum effect, taking both gametes to the fertilization site in the oviduct. Since the sperm contains a Y chromosome, this fertilization gives rise to a XY male embryo.
So, there you have it - without any sperm from another man, a female chimera could become pregnant with a son. The potential theological implications of this are probably best left up to the conscience of the individual reader.
[NCBI via Discover; in the center of the image is an example of a genetic chimera, the result of fusing eggs from the mice on the left and right into a single organism.]