Our careful scientific assessment of basic human sexual physiology—an evaluation completely consistent with our commonsense understanding of human sexual development—clears up the confusion that many experience regarding sex and gender.

On August 9, 2024, Algerian boxer Imane Khelif won the gold medal in women’s boxing at the Paris Olympics. The celebration was clouded, though, by allegations that Khelif wasn’t a woman, but a man boxing against women. If true, at bare minimum, this was unfair. At worst, it was assault. Those defending the boxer countered that since Khelif had no male genitals, the athlete was, therefore, a woman.

Khelif’s sex was a matter of controversy for weeks leading up to and following the gold medal match. The boxer’s medical records were private, however, making a definitive public assessment impossible at the time. Misinformation on sex and sexual development coming from all quarters added to the confusion.

For the first time in history, a precise answer to the question “What is a woman?” is beyond the reach of many otherwise intelligent and educated people. Even U.S. Supreme Court Justice Ketanji Brown Jackson balked when asked during her nomination hearing to provide a definition for the word “woman.” “I’m not a biologist,” she said,^[1] as if biologists were the only ones qualified to distinguish between the sexes.

Yet even some scientists squirm when pressed for a definition. The commonsense definition of “woman” as an adult human female has the consequence of disqualifying biological males who “identify” as females. In the current political climate, this kind of candor ends careers.

The question “What is a woman?” raises other questions. What is a man? Are those the only choices—male or female? If so, why? What distinguishes a male from a female when there are ambiguities in sexual anatomy?

In spite of the current confusion, clear answers to these questions are not difficult to come by. Indeed, the technical criteria have been well known for a long time. The only ones truly confused are modern gender theory advocates and those who listen to them.

How Many Sexes?

Up until the last few beats of human history, there’s been no confusion on the divisions between the sexes, for good reason. The distinctions were obvious. For Homo sapiens, sex is binary. People are born—indeed, conceived—either male or female.

Not so today. Now some biologists and psychologists say there are more than two sexes—even a spectrum of sexual variations often referred to as “sexual identities.” Pop publications push this new narrative. USA Today, for example, tweeted that there are “three different types of sexes.”^[2] Egale, a Canadian LGBT advocacy group, uses a clever rhyme to teach kids that, when it comes to men and women, “You can be both or a mix of the two, or you can be neither if that’s what suits you.”^[3]

To most people, however, these new claims are at odds with common sense. Still, many wonder if they’re missing something. Have there been new discoveries disqualifying what we thought we knew about human sexuality? The answer is no.

Though pockets of our culture are confused about fundamental human nature, there’s no excuse for Christians to be confused. Our Maker confirms through special revelation—Scripture—what we already know from observational common sense: God made humans male and female. Full stop.

Here is the biblical record of God’s sexual design for humanity: “God created man in His own image, in the image of God He created him; male and female He created them” (Gen. 1:27).

When God fashioned the human race, he created two sexes and only two sexes. Jesus confirms this design when, in Matthew 19:4, he cites God’s created order described in Genesis: “Have you not read that He who created them from the beginning made them male and female?” According to both Jesus and Genesis, our Maker made only males and females. Scripture never hints at the possibility of any other variation.^[4] That’s why God’s people have spoken with one voice on this for thousands of years.

We have confirmation of God’s intention for the created order through another source. Scientific research^[5] also verifies the fact that human sexuality is binary, either male or female. During my training as a physical therapist in the 1990s, my professors taught that human sexuality is binary. They weren’t Christians—in fact, one was an outspoken atheist—yet they still understood what nature had made obvious.

Characteristically, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). The Y chromosome contains a specific gene, the SRY gene or “male-determining” gene, that triggers a cascade of genetic events in the human embryo that cause the development of a male body with a penis and testes. Without the SRY gene, the embryo develops into a female body with a vagina and ovaries. This relationship between genes and sex has been understood since its discovery over 100 years ago by biologist Nettie Stevens in 1905^.[6]

That human bodies develop either testes or ovaries is the key to understanding why there are only two sexes. There are only two sexes because there are only two kinds of reproductive cells (gametes) a human can produce. Human bodies are designed to produce either sperm or eggs. There is no other possible gamete—no intermediate “spegg” combination of sperm and egg—that a human body can produce. If there were a third gamete, there would be a third sex. But there isn’t. There are, therefore, only two sexes.

Granted, some human bodies, regardless of chromosomal makeup, are incapable of producing sperm or eggs. This shortcoming, however, doesn’t change our basic understanding of human physiology. For example, human beings walk on two legs; they’re bipedal by nature. However, if someone with a congenital defect is born with only one leg, or if someone loses a leg through an accident, we don’t conclude that humans manifest a spectrum of forms of human locomotion rather than being bipedal. No, humans are still bipedal by nature despite the abnormalities.

In the same way, when people are born with sexual anatomical anomalies that interfere with or prohibit the natural development of male or female sex organs, that doesn’t mean they represent an entirely different sex. The sexual binary classification is not falsified because of biological irregularities.

Intersex

Gender ideology advocates disagree. Not every person can be easily classified as male or female based on chromosomes, they point out, since not all males are XY and not all females are XX. Some people are born intersex, a condition that covers a broad range of chromosomal or anatomical variations that affect a person’s external sex characteristics. A number of variants fall under this heading.

For example, although males typically have XY chromosomes, it’s possible for a male to have XX chromosomes. In de la Chapelle syndrome, the SRY gene is translocated to the X chromosome. The result is a human embryo with XX chromosomes where the male-determining gene triggers the body to develop a penis, testes, and, eventually, sperm. It’s also possible for a female to have XY chromosomes. In Swyer syndrome, a female has XY chromosomes, but a mutation deletes the SRY gene from the Y chromosome. With no male-determining gene directing sexual development, the embryo with XY chromosomes develops a vagina, ovaries, and eggs and is, therefore, female.

Some males are born with XXY chromosomes (Klinefelter syndrome). Some females are born with only one X chromosome (Turner syndrome). Some women over-produce or under-produce sex-related hormones, while others might be born without a vagina (vaginal agenesis). The list goes on, prompting gender theory advocates to conclude that sex is not binary since not all people fit neatly into male or female categories with XY or XX chromosomes or either a penis or a vagina.

Even so, neither chromosomal variations nor the existence of intersex people nullifies the sexual binary or our ability to categorize people as either male or female. Rather, those born with atypical genetics or biology represent variations within the sexual binary categories of male and female, not a negation of them.

Agreed, in rare cases when a child is born, it’s not immediately obvious whether the baby is male or female. According to a 2018 study researching intersex conditions, only one in 2,000 births to one in 4,500 births produces a child with ambiguous genitalia.^[7] In rare conditions where a child’s sex is unclear at birth, it can often be discovered with genetic testing, ultrasound, and other evaluative tools. Note, though, that these methods discover the child’s actual sex that was merely obscured during the initial observations. There is no inherent sexual uncertainty.^[8]

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