A little over three years ago I put up this post to discuss Frank Tipler's argument, using available scientific evidence, for the Virgin Birth of Jesus Christ (from chapter VII of his book, The Physics of Christianity). This Christmas, I want to examine in greater detail the evidence he presents -- in particular, the genetic evidence derived from DNA analysis of blood samples taken from the Shroud of Turin and the Sudarium of Oviedo -- in the hopes that someone more familiar with this branch of molecular biology might pick it up, and either comment on it, take it further, or even (if possible) refute it.
[UPDATE 12/25/2010: A word to my readers: I am well aware of the scorn and ridicule that has been heaped upon Frank Tipler and his theories (here is just one such example). But it is far easier to denigrate than to engage. As you read the post that follows, I would ask that you keep the bigger picture in mind: We have two ancient artefacts, thousands of years old, each with its own independent history -- yet each of which has matching AB-type bloodstains, the source of which tradition assigns to the same person, who was unquestionably of the male gender. How does it turn out, after a scientific analysis possible only in the late twentieth century, that the stains on both cloths lack a key genetic identifier for maleness? That is the question I wish responsible people would address.]
First, some background: the Shroud of Turin, of course, is the name given to what traditionally has been considered as the linen burial cloth in which, as the Gospels all report, the women who prepared Jesus for burial wrapped His body. Its provenance and history are greatly in dispute, a dispute which was heightened by a radiocarbon analysis of a portion of the cloth done in 1988, which dated its origin to no earlier than the 13th century. However, evidence since that well-publicized test has accumulated to cast those results into doubt, and to validate the Shroud's origin as genuine (see the details discussed in this earlier post).
The Sudarium of Oviedo is the name given to the cloth which tradition assigns as the face cloth placed over Jesus' head when he was taken down from the cross, and which was found in the tomb, rolled up and separate from the other linens, after His resurrection (Jn 20:7). (It is not to be confused with the Veil of Veronica, another relic of the crucifixion, which was originally kept at St. Peter's, but is now at the Abbey of Monoppello, high in the Apennines.) The Sudarium's history is entirely different from that of the Shroud's. Its location in Oviedo has been documented since the eighth century; it was in Toledo for about eighty years before that.
Aged, brown blood stains have been described on both cloths for centuries, but actually documented to be human blood (type AB) only with the advanced analysis techniques of the twentieth century. And a recent, in-depth study of the Sudarium done in 1998 (the first ever performed, in contrast to the numerous advanced tests on the Shroud) confirms that the blood stains on each cloth match in placement, blood type, and pattern of spread, along with numerous other correspondences (such as pollen indigenous to Jerusalem) between the two cloths. If the two cloths at one time covered the head, the face and (for the Shroud) the body of the same person, then obviously the 1988 radiocarbon dating of the Shroud was thrown off due to some error in the sampling process.
If a match between the blood stains could be established by forensic analysis of their surviving DNA, then one could feel confident (a) of the Shroud's having a much greater age, and (b) of the absence of fraud or artifice in the creation of the stains and images on each cloth. And this is where Frank Tipler's book referenced above proved most interesting. For in the course of his investigations, he learned that a highly qualified team of researchers from Genoa, Italy -- including two molecular biologists who had invented the standard test for sex determination, had performed DNA analysis on the stains of both the Shroud and the Sudarium in 1995.
However, their results had been published not in a standard scientific journal, available easily to all, but only in an obscure journal in Italian devoted entirely to studies about the Shroud. As Prof. Tipler noted:
Furthermore, only the raw data were published. That is, the Genoa team published black-and-white Xerox copies of the computer output of the DNA analyzer. This is never, never done. Always, the data are presented in a neat table or figure, and they are accompanied by a discussion of their significance. The Genoa team made no effort to interpret their data. . . .
Prof. Tipler, in contrast, had no reluctance in interpreting the data -- that is, once it was arranged in standard tabular form, according to the number of base pairs in the amplicons on the agarose gel which resulted from a polymerase chain reaction (PCR) involving segments of the sample DNA. Now, let me provide a little more background, so those unfamiliar with the procedures of forensic DNA analysis can make sense of that last sentence.
The technique of PCR was developed in 1983 by Kary Mullis, whose TED talk I featured earlier. The idea simply popped into his head one night as he was driving to his vacation cabin in northern California; he tried it, and the results surpassed all his expectations. The technique has been the foundation stone of DNA analysis ever since. Essentially, what it does, given a very small sample of DNA to begin with, is to make millions or even billions of copies of the sample in a "chain reaction" taking about three hours, so that there is enough ending material to analyze with standard laboratory techniques, including chromatography and gel electrophoresis. (Here is an excellent illustrated guide to the whole process.)
The way it works is by first heating the DNA samples to break the two strands of the double helix apart (this is called "DNA denaturation", or "DNA melting"). Once the strands have been separated, they are cooled down and put into a mix of DNA primers (short strands of DNA chosen for their complementarity with the sample being tested) and DNA polymerase -- a magic enzyme which, given a primer, goes to work and replicates the strands of the samples exactly. By successive heatings and coolings, more and more copies of the sample are created, separated into single strands, cooled, and then duplicated again, and again, and again, with the number of DNA copies roughly doubling each time -- hence the "chain reaction."
In running a PCR analysis on their samples from the Shroud and the Sudarion, the Italian researchers included a set of highly particular DNA primers generated from the gene for amelogenin, which plays a role in the building of tooth enamel. This gene appears on both the X- and Y-chromosomes in humans, but in distinctive forms: the allele (gene variant) on the X-chromosome is six base-pairs shorter than the allele on the Y-chromosome. ("Base pairs" are the pairings between the four fundamental nucleotides, or building blocks, of DNA.) And this very slight difference can be used to determine whether any given DNA sample comes from a male or a female, as a result. (Here is a link to a diagram of the genetic code for amelogenin, which shows precisely where the missing base pairs on the X-version differ from the Y-version; note that there are other slight differences between their codes, as well.)
Because of the difference in their respective lengths, the two alleles will show up at different places when the analysis is run on the results of the PCR amplifications (these are the amplicons I mentioned earlier) of the original sample. (In order to understand fully how the analysis produces its results, I highly recommend that those who have the time run through this interactive simulation of the process of gel electrophoresis in the lab.)
The results from female DNA will have only one band of the shorter base-pair length, while the results from male DNA will have two bands, one of the shorter, X-chromosome length, and the other from the longer, Y-chromosome variant of amelogenin. This was the DNA test for gender which was developed by two expert members of the 1995 Italian research team, as mentioned earlier.
The Italian team knew what they were doing. They took steps to eliminate "DNA noise" from contamination of the samples which might have built up from handling of the cloths by various people over the years. Even so, they apparently could not trust the results they ended up with, after all their careful analysis: the genetic signature of both samples, the one from the Shroud, the other from the Sudarium, showed only one band -- for the shorter (106 base-pairs), X-chromosome variant of amelogenin. (Depending on the length of the gene segment used as a primer for the PCR analysis, the X-allele of amelogenin will have either 106, or 212, base pairs, or "bp" -- see the diagram again for a depiction of the different segments used as primers in the test. The extra six base pairs for the Y-allele of amelogenin results in either 112 bp or 224 bp, depending again on the primer that is used for the test.)
With the foregoing as background, we are now ready to appreciate the results of the analysis by the Italian team, as reproduced by Professor Tipler in his book. Here are the results in tabular form, as he arranged them -- according to increasing base-pair length (click on the image to enlarge):
Professor Tipler does not elaborate on this tabular layout, and I have had to deduce, from my earlier experiences with forensic DNA analysis in court, just what the individual columns show. (If I err in any respect in what follows, I trust a knowledgeable commentator will correct me.) The left-hand column shows the index-mark, varying by time of retention, where the band in question appears in the results; in general, a higher index number means a longer retention time, because the segments with the greatest number of base pairs move slowest through the gel. The second column shows the average number of base pairs in that particular band, to a specified tolerance determined by the analysis software. The third column shows the height (intensity) of the band in question, which is proportionate to the amount of that particular allele in the amplified test sample; the total area of the band given in the fourth column also varies proportionately with the intensity. Finally, the number in the fifth column relates to the particular scan of the data run by the computer analyzer.
It is the numbers in the second column with which we are most interested. Both the analysis of the Shroud sample and of the Sudarium sample show results within the range expected for the 106 bp allele of amelogenin: 107.28 for the Shroud, and 105.27 for the Sudarium. (The variation of 1 in either direction from the specific bp number is due to a phenomenon called stutter which can occur during the PCR process -- see the article linked earlier for a more detailed explanation.) But there are no corresponding bands appearing in the 112 bp (+/- 1) range of the data.
This would ordinarily be the genetic signature of a female, with two X-chromosomes, and undoubtedly accounts in part for the reluctance of the Italian researchers to explain or comment on their results. With all of the precautions they took against contamination of the blood samples, how could the Y-allele of amelogenin have completely vanished from both samples, independently, over the years?
As Professor Tipler is at pains to point out, however, the presence of a single X-allele band, and the absence of any Y-allele band, is also consistent with another conclusion: that the person whose blood stained both cloths was that most rare of humans, an XX-male:
I propose that Jesus was a special type of XX male, a type that is quite rare in humans but extensively studied.17 Approximately 1 out of every 20,000 human males is an XX male. Such males are normal in behavior and intelligence but have smaller teeth, shorter stature, and smaller testes than normal males. They are usually identified as XX males because they cannot have children and ask doctors to cure the infertility. Normal males are XY, but there are only twenty-eight genes on the Y chromosome, as opposed to thousands on the X chromosome. Of these twenty-eight genes, fifteen are unique to the Y chromosome and thirteen have counterparts on the X chromosome.18 The genes with counterparts on both the X and the Y chromosomes are called homologous genes. 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 tum off genes was active on these inserted Y genes. (There is an RNA process that can tum off an entire X chromosome. This is the most elegant turnoff mechanism.) Jesus would then have resulted when one of Mary's egg cells started to divide before it became haploid and with the Y genes activated (and, of course, with the extra X genes deactivated)._______________17 Chapelle, Albert de la. 1981. "The Etiology of Maleness in XX Men." Human Genetics 58: 105-116; Guellean, Georges. et al. 1984. "Human XX Males with Y Single-Copy DNA Fragments." Nature 307: 172-73; Page, David C., et al. 1985. "Chromosome-Specific DNA in Related Human XX Males." Nature 315: 224-26; Andersson. Mea. et al. 1986. "Chromosome Y-Specific DNA Is Transferred to the Short Arm of the X Chromosome in Human XX Males." Science 233:786-88; Petit, Christine, et al. 1987. "An Abnormal Terminal X -Y Interchange Accounts for Most but Not All Cases of Human XX Maleness." Cell 49:595-602; Chapelle, Albert de la, et al. 1988. "Invited Editorial: The Complicated Issue of Human Sex Determination." American Journal of Human Genetics 43:1-3.
18 Jegalian, Karin, and Bruce T. Lahn. 2001. "Why the Y Is So Weird." Scientific American, February, 56-61.
Because the full-body image we have from the shroud does not match the parameter of the usual type of XX-male (the 1-in-20,000 example mentioned in the text, in which only the SRY gene is inserted in the X-chromosome, with a resulting smaller stature than other males), Prof. Tipler believes that Jesus may have been an even rarer exemplar -- indeed, a one-time-only species -- of XX-maleness, in which most, if not all, of the fifteen Y-specific genes were inserted into the X-chromosome:
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, between 55,000 and 80,000 years ago. . . . 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/[20,000][20,000] = 1/120 billion.)
How could it be determined if Jesus were in fact such a unique individual? Unfortunately, the tests run by the Italians in 1993 did not search for any Y-genes other than the Y-allele for amelogenin. (Their black-and-white reproduction of their computer data also unfortunately left out the information from the different dye colorings, which would have enabled one to determine just how many different alleles were present, and the degree to which any contamination might have occurred. As it is, their data from just the Shroud show fourteen different alleles present in addition to that from the X-variant of amelogenin, where one would expect at most eight from the four other specific genes for which they tested. Without more data, it is simply not possible to account for the extra six which they show.) Prof. Tipler recommends that more modern tests be conducted on the stains on the two cloths, which could help to determine whether the DNA contains more than just one Y-specific gene, or only one, or two, and could also help to pinpoint any possible sources of contamination. Such tests could moreover dramatically enhance the likelihood that the blood on the separate cloths is from one and the same genetic source. (As it is, the data shows they share three specific alleles already.)
What is one to conclude from all of this? (As I say, I hope that those who are more expert in these subjects will be stimulated to comment, or to write about it on their own blogs.) The point, I emphasize again, is not that science can offer any absolute "proof" or "disproof" of the Virgin Birth. (How God works His miracles will never be fully comprehensible to mortal understanding.) Instead, what fascinates in this investigation of artefacts which are in all likelihood at least two thousand years old is that they hold up so remarkably well to ever closer scrutiny and more extensive examination. There is plenty of room for skeptics to disagree, and for believers to find encouragement. With an open and contrite spirit, not being stubborn or willfully contrary, each individual must form his or her own conclusions, based on what is at hand at the moment. Such is the essence of the grace which God bestows upon us.
A Merry Christmas to all!