There follows an extensive discursus on the phenomenon of parthenogenesis (literally, from the Greek, "virgin birth"😉 in animals as well as in humans. (Yes, I said humans---Prof. Tipler cites the scientific references.) Then he stakes his claim:
I propose that Jesus was a special type of XX male, a type that is quite rare in humans but extensively studied [footnote omitted]. Approximately 1 out of every 20,000 human males is an XX male. . . . An XX male results when a single key gene for maleness on the Y chromosome (the SRY gene) is inserted into an X chromosome. One possibility is that all (or at least many) of the Y chromosome genes were inserted into one of Mary's X chromosomes and that, in her, one of the standard mechanisms used to turn off genes was active on these inserted Y genes. (There is an RNA process that can turn off an entire X chromosome. This is the most elegant turnoff mechanism.) Jesus would then have resulted when one of Mary's eggs started to divide before it became haploid and with the Y genes activated (and, of course, with the extra X genes deactivated). . . .
I hope I have quoted enough here to enable qualified geneticists to ascertain the basis of Professor Tipler's claim to have an explanation for the Virgin Birth of Jesus. As I understand it, the genetics of Jesus would have marked him as an unusually rare male of the species, and if we could somehow have access to a blood sample, we could determine whether or not Professor Tipler's theory was correct. And to give him his due, Prof. Tipler states as much:
If a sample of Jesus' blood and/or flesh could be obtained, my proposal could easily be tested by carrying out two distinct DNA tests for sex: (1) test for the Y genes and (2) test for the two alleles (different gene forms) of X chromosome genes. In other words, a male born of a virgin would have two X chromosome genes for each of its counterpart Y genes. Normal males would only have one X chromosome gene for each Y counterpart gene. This pairing would apply to each of the thirteen genes on the Y chromosome that has an X counterpart.
The odds of such a "virgin birth" would truly be fantastic, as Professor Tipler calculates here:
Such a virgin birth would be improbable. If the measured probability that a single Y gene is inserted into an X chromosome is 1 in 20,000, then the probability that all Y genes are inserted into an X chromosome is 1/20,000 raised to the 28th power, the power corresponding to the number of Y genes. (Assuming that the insertion of each Y gene has equal probability and that these insertions are independent.) There have been only about 100 billion humans born since behaviorally modern Homo sapiens evolved . . . .
Thus, the virgin birth of such an XX male would be unique in human history even if there were only two such Y genes inserted into an X chromosome. (I assume an upper bound to the rate of virgin birth is 1/300. Then the probability of a virgin birth of a male with 2 Y genes is 1/[300][20,000][20,000] = 1/120 billion.) But . . . if such an event had to occur [for God to exist according to physical laws that have shown themselves thus far as true], then the Virgin Birth probability would become 1; that is, certain to occur. In other words, it would be a miracle!
Taken from a Critique of this book: The Physics of Christianity
Manny