Some experiments, though, make one wonder just what, at the end of the day, the researchers were trying to prove. Granted, sometimes results come about unexpectedly; an old college professor of mine once told me that most great scientific breakthroughs were marked not by shouts of "Eureka!" but more often a muttered, "Huh, that's weird."

So when we read a story about an experiment wherein pregnant mice were subjected to abnormally low iron levels, and those mice produced offspring with the XY chromosomes and female reproductive systems, one has to ask, "OK, and therefore, what?"

Textbooks have always taught that this process is 100% dictated by genetics: males have one female and one male chromosome, XY, and females have two female chromosomes, XX. But on Wednesday, the results of a bold experiment with mice were published, showing that very low iron levels in the mother can transform males into females, regardless of their genetics.

“To our knowledge, this is the first demonstration that an environmental factor can influence sex determination in a mammal,” Makoto Tachibana, a biologist at Osaka University in Japan and leader of the research, published in the journal Nature, tells EL PAÍS. “The most important implication of this finding,” he adds, “is that environmental and metabolic conditions influence fundamental developmental decisions that until now were thought to be strictly determined by genetics.”

Well, we've known that for some time, even in mammals. Reptiles and amphibians are far more slippery when it comes to sex than mammals, with some species showing an alarming alacrity in changing dance partners. Some snakes and lizards can even give birth without having mated, in a process called parthenogenesis. 

In the case of this particular experiment, the relevant environmental factor was iron.

The researchers discovered that if iron concentration is reduced by 60% at the cellular level, the testicular gene is switched off. When they reproduced this iron deficiency in pregnant female mice carrying males, they observed that six out of 39 XY offspring were born with two ovaries, a complete sex reversal. Another mouse was born intersex, with one ovary and one testicle.

Now, speaking purely from a biological standpoint, that rates a "wow." The "intersex" example is actually less surprising, as sexual ambiguities can arise from extreme conditions while an embryo is developing. The six mice that had two ovaries are more surprising, but the question is, can these mice reproduce? Almost certainly not; the article is mute on the topic, but I would note that it only mentions testes and ovaries, not the various accessories that go along with those to produce a fully functional reproductive system. And the enzyme mentioned is only related to the production of testes.

Here's the mechanism involved:

Extremely low iron affects the enzyme KDM3A, which modifies a chemical change that turns off the testis-producing gene SRY right at the moment of sex determination. The result is genetically male mice with two ovaries that lived apparently healthy up to eight weeks, although it has not been studied whether they could reproduce — in humans, sex reversal usually leads to infertility.

Ay, that's the rub.

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Nothing like this, to my knowledge, has been observed in humans, and it's not like we can test it; the ethical problems there are staggering. The closest natural correspondent in people is Swyer Syndrome, where a person with an XY chromosome pattern has what appear to be female genitalia, but who never develops testes or ovaries and who never goes through puberty.

Strictly from a biological standpoint, this is one of those things you read and shrug, thinking, "OK, that's mildly interesting." Or at least, that's what I did. But I'll make a prediction here. Once this study finds its way into the hands of the gender theory/transgender activist crowd, it will be ballyhooed as showing that human sexual bipolarity isn't as clear-cut as we know it really is.

That is, of course, horse squeeze. Gender dysphoria, which most, if not all, the "transgender" crowd claim to have, is a psychological, not a genetic, condition, and can and historically has been resolved with therapy, not hormones or surgery. There is a chance-a vanishingly small chance-that at some point in human history, this may have occurred naturally, but the odds are low, especially when you consider that severe anemia, caused by iron deficiency, is dangerous to the point of being life-threatening. But then, like most of the "progressive" left, the gender theory people have never been known for a strict adherence to facts, in biology or anything else.

This was a mildly interesting study performed on mice, with no real practical outcome. And that's all it is.