Biological sex is not as simple as male or female

Sex is messy.

It is not just about chromosomes. Or reproductive cells. Or any other binary metric. Many genetic, environmental and developmental changes can produce those that are thought of as masculine and female traits in the same person. And so sex, scientists say, must be seen in all its complex glory.

“Sex is a multifaceted feature that has some ingredients that are present at birth and some ingredients that have developed during puberty, and each of these ingredients shows changes,” says Sam Sharpe, an evolutionary biologist at Kansas State University in Manhattan.

However, a definition of biological sex presented by US President Donald Trump appoints people as male or female based solely on the size of the reproductive cells they make.

Millions of Americans do not fit this close definition without their fault – and many do not even know it.

In an executive order signed on January 20, the president claims that there are two unchanging human sexes and that women are designated as persons “belonging, in conception, the sex that produces large reproductive cell”. Men, in order, make the cell smaller.

On February 19, the newly created secretary of human health and human services Robert F. Kennedy Jr. announced that the agency, which oversees the most funded health research by the Federation, will use these definitions of policy making.

In a slight difference from the executive order, HHS defines men as people “of sex characterized by a reproductive system with the biological function of sperm production”. And women as people with egg -making systems.

“For me, the definition is really painful because it reduces a human being in their chance to reproduce,” says Anna Bason-Lauber, a pediatric endocrinologist at the University of Friborg in Switzerland.

Moreover, Trump’s definition is not biologically accurate and leaves people who hold certain genetic variants and do not make any reproductive cells, or gametes. The order does not make exceptions to them. “Does what does this mean to people who don’t have a gamete?” Ask Sharpe. “That is, now, an unanswered question. But it’s an important question to answer because you can’t have a sex definition that doesn’t be worth it for everyone.”

Every sex definition used to determine who can get an identification card or use a public bathroom must account for changes, they and other researchers say.

Sex is complicated

One thing that Trump’s order gets right is that there are two sizes of reproductive cells, or gametes, known as eggs and sperm. Egg cells are much larger than semen. This is almost as close to a real binary as nature takes, says Nathan Lens, an evolutionary molecular biologist at John Jay of Criminal Justice in New York City.

But sex is much more than the size of reproductive cells, researchers say.

“Biology does not work very often on the rails,” says Lens.

On the contrary, most of the features attributed to men and women fall along a two -yeast spectrum, an average for women and the other average for men. For example, on average, men are longer than women and have more muscle mass, more red blood cells and a higher metabolism.

But almost no one fits at the peak for all those measures for their sex, says Lens. “There are many women who are higher than many men. There are many women who have higher metabolic rates than some men, although the averages are different.

“If you determine the biological sex simply in the gametes, you will ignore most of what really matters to your daily life, including in your social life,” he says. “Lowering sex on a binary really doesn’t make much sense about how we actually live.”

Sex does not start in conception

No sex cell is produced in conception. Fertilized eggs “cannot produce gametes because they are single cells,” Sharpe says.

In fact, sex development does not start up to a few weeks after conception. The exact time is difficult to determine in people because it occurs in the abdomen, often before people know they are pregnant, says Basonon-Lauber. About six weeks in gestation, cells appear that will eventually create gonads: ovaries to make eggs or tests to produce semen. But for several weeks, she says, those cells are “absolutely indistinguishable” from one another.

Scientists thought that embryos were automatically developed as females unless there were specific guidelines to become male. But in the last decade, researchers found that for embryos to develop as females they need to actively dismantle men’s productive structures and build those that support women’s reproduction.

In about eight weeks of gestation, some cells in those that will be done tests begin to make testosterone hormone, which is important for the development of scrotum and penis and other male reproductive organs. But men still do not produce semen at this point. This is partly because testosterone production falls around the 20th week of pregnancy and does not again get back to puberty, when it begins once again, allowing immature cells to morphite.

The ovaries do not produce any sex hormone in the fetus. And the uterus, the fallopian tubes and the vagina develop without any contribution from the hormones, says Basonon-Lauber. Women are born with all the eggs they will ever make, though those cells are stuck in suspended animation to puberty, when they can be baked and released.

Sex chromosomes change

These developmental processes are directed in part from what are often called sex chromosomes. The name is somewhat wrong because these two chromosomes – called X and Y – have a wide range of responsibilities beyond sex.

Chromosome X contains hundreds of genes, including many involved in processes throughout the body, such as blood clotting, color vision and brain development. The much smaller Y chromosome contains important genes for the development of masculine sex and fertility, but also plays a role in immunity, heart health and cancer.

Women generally have two X chromosomes, while men usually have an X chromosome and a Y. But there are many changes in the subject, says Basonon-Lauber. For example, in Turner syndrome, women lack an X X. chromosome. “They have no gametes,” she says. On the contrary, these women have what are called ribbon gonads. “They have a piece of collagen instead of the ovaries.” They have a uterus.

This leads the bason-lauber to ask herself, “If a woman’s definition is the presence of large cells, what are these [people]? “Turner’s syndrome is not so rare, she says, occurring at 1 from every 2,000 to 2,500 babies born. Some people are not diagnosed until adulthood or can never be diagnosed.

About 1 in every 650 male babies born have two or more X chromosomes and one Y. Those men who have Klinefelter syndrome do not produce semen. Many are not aware that they carry an additional chromosome until they go for fertility treatments, says Basonon-Lauber. These people have tests and penis, but they do not make small reproductive cells, and thus do not fit the administration’s definition for men.

The Y chromosome contains a gene called fuck This is important, but not essential, for the development of male sex. Sometimes, when chromosomes are separated before sperm production, fuck It is thrown from the Y chromosome and attaches to itself on an X or another chromosome. When hitchhiking fuck Gene, but not the rest of the Y chromosome, passes to offspring who can result in people who have two x chromosomes plus a stroller fuck finds those people often develop as men.

Some people have an X chromosome and a y but hold a version of fuck or other genes that do not promote typical male development. Those people develop like women, but do not make gametes.

Other people with an X and AY may have genetic variants that prevent their bodies from responding to testosterone and other male sex hormones, called androgens. Those people with androgen insensitivity have tests within their abdomen, but the rest of their bodies develop as women. “These people would have small cells, but they are not men,” says Bason-Lauber.

Variants in many other genes can also prevent the production of large or small reproductive cells. Some people even have different combinations of sex chromosomes in different cells in their body.

Being intersex is not so rare

About 1.7 percent of the population is intersex and does not fit masterfully into male and female boxes, according to Interract, an advocacy organization for young Intersx. This is as common as having of course red hair. People intersex can have a wide variety of sex development changes, including Turner syndrome, androgen insensitivity, Klinefelter syndrome and others.

Some may arise with ovarian and testicular tissues, and thus can be classified as male and female under the conditions of the executive order, says Sylvan Fraser Anthony, the legal director and interact policy.

Intersexual individuals are often subject to surgery as infants or young children to make their genitals or internal organs in accordance with the sex their parents choose. They may also need to take hormones such as estrogen or testosterone to maintain their health, says Sharpe, who worries that a binary sex definition can be used to deny people intersex access to health care.

Such sexual hormones also “play an important role in many aspects of development, including whether your skin is dry or not, or how long you grow during puberty, or if you are able to maintain bone density,” They say.

The choice of any single sex determinant is obliged to plant confusion.

“If [they] Use chromosomes, there are many individuals who will be surprised to learn that they are men, “says lennts.” If they use gametes, they will exclude some individuals … but they will also potentially open the door to include people who do not They intended. ”For example, people who have X and Y chromosomes but make female gametes would be acceptable under the definition to compete in women’s sports.

“Biology of sex and gender makes it very clear,” says Lens. “These are not difficult categories with clear definitions.”