Microchimerism

Microchimerism is a term that refers to the phenomena of cells or genetic material from another organism being present and integrated into an organism's body. Specifically, when referring to humans, it is often used to refer to the idea that women's bodies are infused with the DNA of their previous male sexual partners (that they engage in unprotected sexual intercourse with), or their male offspring (carried to term or not). Technically, this is called male microchimerism.

Microchimerism can also occur in infants of both sexes due to them absorbing maternal tissue from the placenta in the womb, which is known as maternal microchimerism. It is also highly plausible that it can derive from stem cells in breast milk. This form of chimerism is hypothesized to confer several benefits to the infant, including superior immune system functioning and faster tissue healing, benefits that may accrue throughout the infant's life cycle. Organ transplants and blood-transfusions are other likely sources of microchimerism in humans.

It has been speculated that this male DNA or RNA could influence their subsequent offspring's traits and possibly also influence the women's own phenotype, which is known as telegony. The evolutionary advantage would be that the genes would replicate in a different organism, increasing reproductive success via a separate pathway than direct fertilization of the egg cells. It has also been claimed that maternal microchimerism can even promote greater reproductive success among the mother in a non-mendelian fashion by attenuating the immune system of female offspring to paternal immune system antigens they share in common with the mother of the offspring, thereby reducing the rates of fetal rejections among the female offspring partnered with such men.

Microchimerism continues to be a contentious and taboo concept in humans, especially when linked to claims that unprotected sexual intercourse as a source of male chimerism in females. It is often derided as a long-debunked example of pseudo-science. However, new research hypothesizing that unprotected sexual intercourse is a potential source of male microchimerism in women has led to the idea that this is a potential mechanism via which telegony can operate in humans, thereby promoting a resurgence of widespread interest in the topic.

History of the concept

The idea of telegony was first formally developed by the Greek Philosopher and proto-scientist Aristotle. Telegony is the notion that females and their offspring acquire traits from their mothers' prior sex partners, particularly their first partner. These traits were thought to stem from the 'impression' a woman's first sexual partner would make upon her, with this impression sometimes believed to be metaphysical in form. The theory of telegony was thus closely linked to the once widespread notion of 'maternal impressions' (the idea that a strong psychological shock experienced by a woman during pregnancy could affect the phenotype of her subsequent offspring).

The concept of telegony was well known to animal breeders throughout history, and was mentioned obliquely in the story of Jacob's spotted sheep in the book of Genesis. However, this tale is more of an example of the concept of sympathetic magic than telegony proper (a form of magic involving representations of the object(s) one wishes to influence, voodoo dolls being an example of this).

This ancient concept was first subjected to some level of empirical scrutiny in the Victorian era with the famous case of Lord Morton's Mare. Charles Darwin mentioned this case in his 1868 book The Variation of Animals and Plants Under Domestication, in which Darwin introduced a more scientific theory of telegony mediated by sperm molecules. Lord Morton had bred a thoroughbred chestnut coloured Arabian mare with a quagga (a now-extinct subspecies of Zebra) and then bred it with a black stallion. The two foals born to the stallion were heavily striped, which was widely thought to be definitive proof of telegony.

In his 1893 work, An Examination of Weissmanism, the Canadian evolutionary biologist George Romanes outlined a number of supposed 'confirmed cases' of telegony he had examined, including in pigs, dogs, donkeys and horses. Romanes raised these alleged cases via reference to two competing theories of heredity popular at the time, namely, Darwin's pangenesis theory that the male germ cells contained 'gemmules' that would be integrated into the mother's body and would henceforth influence the character of subsequent offspring borne by her, and the German biologist August Weissmann's theory of 'germ plasm' which delineated the germ cells and somatic cells of the body via a 'Weissman barrier', which was thought to have abrogated the concept of non-heritable traits being passed on (basically a nascent concept of genes). Romanes claimed this effect was most pronounced 'when the first sire is of a relatively stable and also of a markedly different ancestral stock from the dam' and was otherwise exceedingly rare.

Later, after Gregor Mendel's experiments on inheritance, the concept of non-inherited characteristics being passed on was believed to be debunked, with the case of Morton's Mare thought to be an example of an atavism or a product of dominant and recessive genes causing traits to skip one or more generations. The concept of telegony was largely discarded in scientific circles, together with Lamarck's theory of evolution via acquired traits. Though some still held to the idea, with the Philosopher Otto Weininger briefly mentioning telegony in his magnum opus Sex and Character as being caused by the overwhelming influence a woman's "absolute sexual complement" exerts on her when she engages in intercourse with him.

In modern times, chimerism (alien cells being found within an organism) increasingly became a topic of research in the medical community after the advent of successful organ transplantation methods. It was in this context that the term 'microchimerism' was coined in 1974, referring to the observation that a small portion of donor bone marrow cells survived long-term in mice who had previously been infused with the bone marrow of donor mice.

Since then, further research into the phenomenon found that microchimerism can be persistent and not just temporary in both animals and humans and could be spread by other ways than organ or tissue transplantation, such as the two-way transfer of cells that occurs during pregnancy in several mammalian species, including humans.

Further research into the potential origins of male microchimerism in women and the potential role of male microchimerism in the etiology of several diseases led to speculation that unprotected sexual intercourse is one potential source of microchimerism in mammals. This led to further speculation that microchimerism is one possible mechanism via which telegony may operate in humans, along with hypothesized epigenetic changes in the mother being induced by the absorption of DNA and RNA contained in male germ cells into the somatic cells of the body after unprotected sexual intercourse, with the latter being essentially a modern version of Darwin's pangenesis theory.

Sexual intercourse as a possible source of male microchimerism in women

In the early 2000s, after the discovery of male DNA inside the bodies of women, researchers crafted several hypotheses to explain this phenomenon. These included transfer from previous male sexual partners (that they engage in unprotected sexual intercourse with) and transfer from male offspring (carried to term fully or not), which is called fetal microchimerism. The first known study published on this was in October 2002, with research into the subject still ongoing.

A good critique of studies trying to determine the causes of male microchimerism in women is that these studies have only looked at parity (whether any offspring have been carried to full term, regardless of whether the child survives or not, particularly sons when it comes to this subject) and not gravidity (total offspring conceived) among women.

To rule out fetal transfer as the only source of male microchimerism in women, you can only look at cases of nulligravida: women or girls who never even conceived a fetus. The easiest way to get female subjects confirmed to be completely nulligravid would be to examine prepubescent girls, since they cannot conceive a fetus.

Müller et al. (2015) examined a cohort of Danish girls that were stated to be nulliparous (not having borne children) aged 10-15 (n=154) and discovered evidence of male microchimerism in 13.6% of the sample. They found a higher likelihood of male chimerism in females whose mothers had received blood transfusions or had previously given birth to male offspring but stated that only half of the male chimerism found could be attributed to these factors. It was also discovered that there was a positive correlation between the age of the girls and their likelihood of testing positive for male microchimerism.

Despite these trends, they claimed that not all instances of male chimerism in the girls could be explained via prenatal exposure to prior male microchimerism on behalf of their mothers, and they concluded:

• "We speculate that sexual intercourse may be important but other sources of male cells likely exist in young girls."

Other studies

There have been scarce studies validating the concept of sexual intercourse resulting in the microchimerism of male DNA and RNA in the female body. This area represents a relatively novel field of research that is likely being hindered by the potential political and social implications of these phenomena being common in humans. A brief overview of some of the relevant research into the matter follows:

• Jørgensen et al. (2012) examined (n=272) female participants in a separate Danish longitudinal dietary study for evidence of male microchimerism. They commented: "We assumed male microchimerism to originate from pregnancies with a male fetus. Contrary to what we expected, we found no obvious association between the number of live-born boys and detection of male microchimerism." They stated that: "Also, a prior study of male microchimerism and breast cancer by Gadi et al. reported 33% of healthy control women without sons to test positive." They left the question open regarding the potential sources of this male chimerism in their female subjects, writing: "Although not yet studied, sexual intercourse without pregnancy has also been hypothesized as a source of male microchimerism. Information on sexual habits was not collected in this study, which is why we could not pursue the possibility that either current or past sexual activity could predict male microchimerism positivity."
• Chan & Nelson (2013), utilizing real-time polymerase chain reaction technique, found that 63% of the women in their sample exhibited male microchimerism. They also found a very tentative link between this male chimerism and Alzheimer's disease, concluding, "We found brain Mc (microchimerism) to be relatively frequent in humans and widely distributed in this organ. Our data also suggested a lower prevalence of brain Mc in women without Alzheimer disease than women without neurological disease."
• Zagoskin MV, Davis RE, & Mukha DV (2017) studied the semen samples of 'three 30 year old men' and found: "We have shown that human seminal plasma contains a repertoire of cell-free dsRNA. We do realize that the identity, source, and functioning of these dsRNA are yet undetermined. We hypothesize that these dsRNAs could influence the implementation of genetic information or gene regulation in offspring." They also speculated, based on the previous research by Crean et al. (in fruit flies), that nucleic acids found in human semen may possible penetrate in the immature oocytes (egg cells) found in the women's ovary, and therefore potentially allow the women's subsequent offspring to inherit characteristics of her prior male sex partners, writing "We suggest that one of the possible functions of dsRNA in human seminal plasma may be to influence human oocytes and therefore, influence the offspring. They called for more research to be performed on the subject of telegony, (e.g. in other mammalian species such as dogs).
• Crean et al. (2014) conducted a study that demonstrated the existence of telegony in flies (Telostylinus angusticollis) finding: "Although the second male sired a large majority of offspring, offspring body size was influenced by the condition of the first male". They concluded that this finding of non-parental genetic transmission had important implications for evolutionary theorists: "The potential for such effects exists in any taxon characterized by internal fertilization and polyandry, and such effects could influence the evolution of reproductive strategies."

Potential Implications

If microchimerism transferred through the emission of semen, thereby resulting in telegony, was proven to exist in humans, it would demonstrate provide an example of very tangible and lasting consequences to unrestricted female promiscuity. Some women however, see the concept of telegony as arousing and amusing—it would mean that their prior desirable sexual partners have potentially left a permanent impression upon them and their offspring. Men would also potentially become jealous at the likelihood of being 'micro-cucked' by their wives or girlfriends prior sexual partners.

Traditionalists also frequently use the purported existence of telegony as a rhetorical point to emphasize what they view as the strong drawbacks of widespread female sexual license. The concept is cited by some traditionalists as evidence that women that aren't virgins are irredeemably "tainted", and they claim that the concept if validated, proves the wisdom of traditionalist practices that insisted (and still do in some regions) on the virginity of the woman before marriage. The concept of telegony is apparently promoted in Traditionalist Russian Orthodox circles, with the current Children's Rights Commissioner for the President of the Russian Federation, Anna Kuznetsova, being an outspoken prominent proponent of the theory. Though she backtracked somewhat when she was subjected to widespread vituperation due to her views on the subject.

There is also tentative evidence possibly linking male and fetal microchimerism to a host of health problems, including auto-immune disease (increased risk only found after "induced abortion"), increased risk of certain cancers (though it may actually be associated with an increased chance of surviving certain cancers), and evidence linking greater levels of male chimerism in the female brain with Alzheimer's disease.

The concept—if validated—would also be of interest in the fields of evolutionary biology and evolutionary psychology since it would possibly be a factor in explaining the male urge to 'mate-guard', and would potentially also influence the reproductive strategies pursued by organisms of either sex. It would likely also be of interest to those in the field of medicine and psychology, as the male chimerism (found in the brain) may potentially influence the psychology and, therefore, the behavior of the females who have been chimerized by male cells.

Theoretically, it could also be possible to discern a woman's number of prior sexual partners (that she had unprotected sexual intercourse with) by examining her DNA for signs of male microchimerism and extrapolating the total amount of male chimerism in her genome.

See also

• Reproductive success
• Mutation
• Paternity assurance