Microchimerism: Studies Show How Previous Sex Partners Can Affect Offspring

Maybe sex is a bigger deal than we thought. Studies on flies have found that the first mate can affect a mother's offspring – despite not being the dad.

By Nicole Dominique2 min read
Pexels/Юлиана Маринина

Is sex really just a physical act? Society has normalized casual hookups, one-night stands, and FWB relationships. While I’m not shaming these acts or condemning those who’ve done them, I do find it hard to believe that sex would have little to no effect on your health or biology. 

Researchers at the University of New South Wales, Australia, tend to agree and may have provided us with scientific findings to support the idea that offspring can resemble a mother's previous sexual partner – kind of. They did the study with flies, but let's not forget how flies are used as a tool in human disease research.

Research fellow Angela Crean reveals how offspring size is determined by the first male the mother mated with – emphasis on the first male, not the current dad of the offspring. “The genetic tests showed that even though the second male fertilized the eggs, the offsprings’ size was determined by the condition of the first male,” she says. “The cool thing is that the non-genetic effects we are seeing are not necessarily tied to the fertilization itself.”

This idea actually dates all the way back to Aristotle, who alleged that the characteristics of the one who “deflowers” the virgin will go on to pass to the direct – and indirect – offspring.

The implication of this is that previous sexual partners may leave a long-standing legacy in females. A previous study on fruit flies further supports this theory when researchers at the University of East Anglia discovered how semen could take control of female flies' genes. "It’s already known that seminal fluid proteins transferred from males during mating cause remarkable effects in females – including altered egg laying, feeding, immunity, sleep patterns, water balance, and sexual receptivity," lead researcher Professor Tracey Chapman explains. "We tested here the effects of one enigmatic seminal fluid protein, known as the ‘sex peptide,’ and found it to change the expression of a remarkable array of many genes in females – both across time and in different parts of the body."

Chapman also called the semen protein a "master regulator," meaning that males have a "direct and global influence on the behavior and reproductive system of the female," and that "such effects may well occur across many species." 

Fascinatingly (or disturbingly to some), this “theory” known as telegony is a wide-held belief among professional animal breeders. This idea actually dates all the way back to Aristotle, who alleged that the characteristics of the one who “deflowers” the virgin will go on to pass to the direct – and indirect – offspring. In the 19th century, Lord Morton bred a white mare with a quagga stallion, but when he later bred that same mare with a white stallion, the offspring apparently came out with striped legs like the quagga.

In 2005, an assessment published by The American Journal of Medicine proved that male microchimerism (the presence of a small number of cells or DNA in a person that originated from another) was found in women without sons. Levels of the male cells were significantly higher in the induced abortion group. 

Look this same topic up on Google, and you’ll find that many articles describe this theory as “false” and “understudied.” However, the funding of science is broken, and genuine studies with real results are few in number. For example, clinical trials funded by Big Pharma have a 27% higher odds of reaching "favorable results" compared to publicly funded trials, according to Scientific American. Research funding from other industries – like food, beverage, and automobile companies – is also growing in number, diluting the studies funded by well-intentioned individuals done by genuine investigators. What I’m saying is, perhaps the reason why there are few studies on promiscuity and its effects on people can be boiled down to this: Sex sells.

Don’t miss anything! Sign up for our weekly newsletter and get curated content weekly!