Why do the two sexes have different reproductive costs and capabilities?

Why do the two sexes have different reproductive costs and capabilities?

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Is there an evolutionary explanation that shows why the reproductive costs are mostly on the female sex? And therefore, why do males can potentially have more offspring?

Does that happen to create more competition in sexual selection?

I may have misunderstood your question, but there is no theory why usually reproductive costs are on the female, as this is a fact. Females have usually larger (and fewer) reproductive cells (gametes), they frequently have to carry the embryo until birth, and sometimes they have to attend to the offspring during the first stages of their lives. To put it very simple, females are stuck with their offspring from the moment of conception until they are born - sometimes even longer - while males generally can mate with many females in a short period of time, potentially having much more offspring.

A consequence of this is that, usually, females are choosy (they want good mates), whereas males just try to mate as much as possible. Female choosiness generates sexual competition, as females prefer to mate with males having certain characteristics that hint to a superior genotypes/phenotype that may be passed to their prole (e.g. beautiful plumage, social status, size of the wallet). Sometimes the costs of attending offspring after birth are higher than the costs associated with reproduction alone. In some of these cases, we may observe unusual behaviors, e.g. male-only parental care and choosy males.

This is a very broad and complex topic and a short answer here cannot cover all of it. John Maynard Smith developed the game theory approach most commonly used to investigate the consequences of different pay-offs for the two sexes and to explore how these can influence the behavior of the parents. Moreover, this topic is also covered in many behavioral biology textbooks. I have had very positive experiences with Krebs & Davis Behavioural Ecology (ISBN-13: 978-0865427310), which I would recommend.

Hope to have clarified some of your doubts.



Within a two-sex species, there are roughly three possible evolutionary strategies for reproductive investment: Sex A and Sex B invest equally. Sex A invests more than Sex B. Sex B invests more than Sex A.

The last two are practically equivalent if you don't project your assumptions about differences between the sexes.

So the only alternative to different reproductive investments is equal reproductive investments. That option is not stable since sex A can invest 10% less at only 5% (assuming a linear relationship between investment and reproductive success, which is not accurate) reduced viability since the partner is not investing more yet. This means sex A can use the saved energy to reproduce with 10% more partners. This is a constant evolutionary pressure, so eventually one sex will invest a lot less than the other.

The other sex will probably not invest 5% less too, since that drops offspring viability by another 5% meaning they gain 10% more partners at the cost of 10% less offspring. There is no advantage here, so there is no evolutionary pressure. Alternatively, they could invest 5% more leading to 5% more reproductive success. This also gives no advantage.

The only reason for any sex to increase investment is if the reproductive success gets so low that it it is worth a larger investment to keep reproducing. There is no reason to assume the investment will primarily come from the smaller investing sex, so that won't change the difference in investments.


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Cross-fertilization, also called Allogamy, the fusion of male and female gametes (sex cells) from different individuals of the same species. Cross-fertilization must occur in dioecious plants (those having male and female organs on separate individuals) and in all animal species in which there are separate male and female individuals. Even among hermaphrodites—i.e., those organisms in which the same individual produces both sperm and eggs—many species possess well-developed mechanisms that ensure cross-fertilization. Moreover, many of the hermaphroditic species that are capable of self-fertilization (q.v.) also have capabilities for cross-fertilization.

There are a number of ways in which the sex cells of two separate individuals can be brought together. In lower plants, such as mosses and liverworts, motile sperm are released from one individual and swim through a film of moisture to the egg-bearing structure of another individual. In higher plants, cross-fertilization is achieved via cross-pollination, when pollen grains (which give rise to sperm) are transferred from the cones or flowers of one plant to egg-bearing cones or flowers of another. Cross-pollination may occur by wind, as in conifers, or via symbiotic relationships with various animals (e.g., bees and certain birds and bats) that carry pollen from plant to plant while feeding on nectar.

Methods of cross-fertilization are equally diverse in animals. Among most species that breed in aquatic habitats, the males and females each shed their sex cells into the water and external fertilization takes place. Among terrestrial breeders, however, fertilization is internal, with the sperm being introduced into the body of the female. Internal fertilization also occurs among some fishes and other aquatic breeders.

By recombining genetic material from two parents, cross-fertilization helps maintain a greater range of variability for natural selection to act upon, thereby increasing a species’s capacity to adapt to environmental change.

Sex Change: Physically Impossible, Psychosocially Unhelpful, and Philosophically Misguided

Contrary to the claims of activists, sex isn’t “assigned” at birth—and that’s why it can’t be “reassigned.” As I explain in my book When Harry Became Sally: Responding to the Transgender Moment, sex is a bodily reality that can be recognized well before birth with ultrasound imaging. The sex of an organism is defined and identified by the way in which it (he or she) is organized for sexual reproduction.

This is just one manifestation of the fact that natural organization is “the defining feature of an organism,” as neuroscientist Maureen Condic and her philosopher brother Samuel Condic explain. In organisms, “the various parts … are organized to cooperatively interact for the welfare of the entity as a whole. Organisms can exist at various levels, from microscopic single cells to sperm whales weighing many tons, yet they are all characterized by the integrated function of parts for the sake of the whole.”

Male and female organisms have different parts that are functionally integrated for the sake of their whole, and for the sake of a larger whole—their sexual union and reproduction. So an organism’s sex—as male or female—is identified by its organization for sexually reproductive acts. Sex as a status—male or female—is a recognition of the organization of a body that can engage in sex as an act.

That organization isn’t just the best way to figure out which sex you are it’s the only way to make sense of the concepts of male and female at all. What else could “maleness” or “femaleness” even refer to, if not your basic physical capacity for one of two functions in sexual reproduction?

The conceptual distinction between male and female based on reproductive organization provides the only coherent way to classify the two sexes. Apart from that, all we have are stereotypes.

This shouldn’t be controversial. Sex is understood this way across sexually reproducing species. No one finds it particularly difficult—let alone controversial—to identify male and female members of the bovine species or the canine species. Farmers and breeders rely on this easy distinction for their livelihoods. It’s only recently, and only with respect to the human species, that the very concept of sex has become controversial.

And yet, in an expert declaration to a federal district court in North Carolina concerning H.B. 2 (a state law governing access to sex-specific restrooms), Dr. Deanna Adkins stated, “From a medical perspective, the appropriate determinant of sex is gender identity.” Adkins is a professor at Duke University School of Medicine and the director of the Duke Center for Child and Adolescent Gender Care (which opened in 2015).

Adkins argues that gender identity is not only the preferred basis for determining sex, but “the only medically supported determinant of sex.” Every other method is bad science, she claims: “It is counter to medical science to use chromosomes, hormones, internal reproductive organs, external genitalia, or secondary sex characteristics to override gender identity for purposes of classifying someone as male or female.”

In her sworn declaration to the federal court, Dr. Deanna Adkins called the standard account of sex—an organism’s sexual organization—“an extremely outdated view of biological sex.” Dr. Lawrence Mayer responded in his rebuttal declaration: “This statement is stunning. I have searched dozens of references in biology, medicine and genetics—even Wiki!—and can find no alternative scientific definition. In fact the only references to a more fluid definition of biological sex are in the social policy literature.” Just so. Dr. Mayer is a scholar in residence in the Department of Psychiatry at the Johns Hopkins University School of Medicine and a professor of statistics and biostatistics at Arizona State University.

Modern science shows that our sexual organization begins with our DNA and development in the womb, and that sex differences manifest themselves in many bodily systems and organs, all the way down to the molecular level. In other words, our physical organization for one of two functions in reproduction shapes us organically, from the beginning of life, at every level of our being.

Cosmetic surgery and cross-sex hormones can’t change us into the opposite sex. They can affect appearances. They can stunt or damage some outward expressions of our reproductive organization. But they can’t transform it. They can’t turn us from one sex into the other.

“Scientifically speaking, transgender men are not biological men and transgender women are not biological women. The claims to the contrary are not supported by a scintilla of scientific evidence,” explains Dr. Mayer.

Or, as Princeton philosopher Robert P. George put it, “Changing sexes is a metaphysical impossibility because it is a biological impossibility.”

Psychosocial Outcomes

Sadly, just as “sex reassignment” fails to reassign sex biologically, it also fails to bring wholeness socially and psychologically. As I demonstrate in When Harry Became Sally, the medical evidence suggests that it does not adequately address the psychosocial difficulties faced by people who identify as transgender.

Even when the procedures are successful technically and cosmetically, and even in cultures that are relatively “trans-friendly,” transitioners still face poor outcomes.

Dr. Paul McHugh, the University Distinguished Service Professor of Psychiatry at the Johns Hopkins University School of Medicine, explains:

Transgendered men do not become women, nor do transgendered women become men. All (including Bruce Jenner) become feminized men or masculinized women, counterfeits or impersonators of the sex with which they “identify.” In that lies their problematic future.

When “the tumult and shouting dies,” it proves not easy nor wise to live in a counterfeit sexual garb. The most thorough follow-up of sex-reassigned people—extending over thirty years and conducted in Sweden, where the culture is strongly supportive of the transgendered—documents their lifelong mental unrest. Ten to fifteen years after surgical reassignment, the suicide rate of those who had undergone sex-reassignment surgery rose to twenty times that of comparable peers.

Dr. McHugh points to the reality that because sex change is physically impossible, it frequently does not provide the long-term wholeness and happiness that people seek.

Indeed, the best scientific research supports McHugh’s caution and concern.

Here’s how the Guardian summarized the results of a review of “more than 100 follow-up studies of post-operative transsexuals” by Birmingham University’s Aggressive Research Intelligence Facility (Arif):

Arif, which conducts reviews of healthcare treatments for the NHS, concludes that none of the studies provides conclusive evidence that gender reassignment is beneficial for patients. It found that most research was poorly designed, which skewed the results in favour of physically changing sex. There was no evaluation of whether other treatments, such as long-term counselling, might help transsexuals, or whether their gender confusion might lessen over time.

“There is huge uncertainty over whether changing someone’s sex is a good or a bad thing,” said Chris Hyde, the director of Arif. Even if doctors are careful to perform these procedures only on “appropriate patients,” Hyde continued, “there’s still a large number of people who have the surgery but remain traumatized—often to the point of committing suicide.”

Of particular concern are the people these studies “lost track of.” As the Guardian noted, “the results of many gender reassignment studies are unsound because researchers lost track of more than half of the participants.” Indeed, “Dr. Hyde said the high drop out rate could reflect high levels of dissatisfaction or even suicide among post-operative transsexuals.” Dr. Hyde concluded: “The bottom line is that although it’s clear that some people do well with gender reassignment surgery, the available research does little to reassure about how many patients do badly and, if so, how badly.”

Arif conducted its review back in 2004, so perhaps things have changed in the past decade? Not so. In 2014, a new review of the scientific literature was done by Hayes, Inc., a research and consulting firm that evaluates the safety and health outcomes of medical technologies. Hayes found that the evidence on long-term results of sex reassignment was too sparse to support meaningful conclusions and gave these studies its lowest rating for quality:

Statistically significant improvements have not been consistently demonstrated by multiple studies for most outcomes. … Evidence regarding quality of life and function in male-to-female (MtF) adults was very sparse. Evidence for less comprehensive measures of well-being in adult recipients of cross-sex hormone therapy was directly applicable to GD patients but was sparse and/or conflicting. The study designs do not permit conclusions of causality and studies generally had weaknesses associated with study execution as well. There are potentially long-term safety risks associated with hormone therapy but none have been proven or conclusively ruled out.

The Obama administration came to similar conclusions. In 2016, the Centers for Medicare and Medicaid revisited the question whether sex reassignment surgery would have to be covered by Medicare plans. Despite receiving a request that its coverage be mandated, they refused, on the ground that we lack evidence that it benefits patients. Here’s how the June 2016 “Proposed Decision Memo for Gender Dysphoria and Gender Reassignment Surgery” put it:

Based on a thorough review of the clinical evidence available at this time, there is not enough evidence to determine whether gender reassignment surgery improves health outcomes for Medicare beneficiaries with gender dysphoria. There were conflicting (inconsistent) study results—of the best designed studies, some reported benefits while others reported harms. The quality and strength of evidence were low due to the mostly observational study designs with no comparison groups, potential confounding and small sample sizes. Many studies that reported positive outcomes were exploratory type studies (case-series and case-control) with no confirmatory follow-up.

The final August 2016 “Decision Memo for Gender Dysphoria and Gender Reassignment Surgery” was even more blunt. It pointed out that “Overall, the quality and strength of evidence were low due to mostly observational study designs with no comparison groups, subjective endpoints, potential confounding (a situation where the association between the intervention and outcome is influenced by another factor such as a co-intervention), small sample sizes, lack of validated assessment tools, and considerable lost to follow-up.” That “lost to follow-up,” remember, could be pointing to people who committed suicide.

And when it comes to the best studies, there is no evidence of “clinically significant changes” after sex reassignment:

The majority of studies were non-longitudinal, exploratory type studies (i.e., in a preliminary state of investigation or hypothesis generating), or did not include concurrent controls or testing prior to and after surgery. Several reported positive results but the potential issues noted above reduced strength and confidence. After careful assessment, we identified six studies that could provide useful information. Of these, the four best designed and conducted studies that assessed quality of life before and after surgery using validated (albeit non-specific) psychometric studies did not demonstrate clinically significant changes or differences in psychometric test results after GRS [gender reassignment surgery].

In a discussion of the largest and most robust study—the study from Sweden that Dr. McHugh mentioned in the quote above—the Obama Centers for Medicare and Medicaid pointed out the nineteen-times-greater likelihood for death by suicide, and a host of other poor outcomes:

The study identified increased mortality and psychiatric hospitalization compared to the matched controls. The mortality was primarily due to completed suicides (19.1-fold greater than in control Swedes), but death due to neoplasm and cardiovascular disease was increased 2 to 2.5 times as well. We note, mortality from this patient population did not become apparent until after 10 years. The risk for psychiatric hospitalization was 2.8 times greater than in controls even after adjustment for prior psychiatric disease (18%). The risk for attempted suicide was greater in male-to-female patients regardless of the gender of the control. Further, we cannot exclude therapeutic interventions as a cause of the observed excess morbidity and mortality. The study, however, was not constructed to assess the impact of gender reassignment surgery per se.

These results are tragic. And they directly contradict the most popular media narratives, as well as many of the snapshot studies that do not track people over time. As the Obama Centers for Medicare and Medicaid pointed out, “mortality from this patient population did not become apparent until after 10 years.” So when the media tout studies that only track outcomes for a few years, and claim that reassignment is a stunning success, there are good grounds for skepticism.

As I explain in my book, these outcomes should be enough to stop the headlong rush into sex-reassignment procedures. They should prompt us to develop better therapies for helping people who struggle with their gender identity. And none of this even begins to address the radical, entirely experimental therapies that are being directed at the bodies of children to transition them.

The Purpose of Medicine, Emotions, and the Mind

Behind the debates over therapies for people with gender dysphoria are two related questions: How do we define mental health and human flourishing? And what is the purpose of medicine, particularly psychiatry?

Those general questions encompass more specific ones: If a man has an internal sense that he is a woman, is that just a variety of normal human functioning, or is it a psychopathology? Should we be concerned about the disconnection between feeling and reality, or only about the emotional distress or functional difficulties it may cause? What is the best way to help people with gender dysphoria manage their symptoms: by accepting their insistence that they are the opposite sex and supporting a surgical transition, or by encouraging them to recognize that their feelings are out of line with reality and learn how to identify with their bodies? All of these questions require philosophical analysis and worldview judgments about what “normal human functioning” looks like and what the purpose of medicine is.

Settling the debates over the proper response to gender dysphoria requires more than scientific and medical evidence. Medical science alone cannot tell us what the purpose of medicine is. Science cannot answer questions about meaning or purpose in a moral sense. It can tell us about the function of this or that bodily system, but it can’t tell us what to do with that knowledge. It cannot tell us how human beings ought to act. Those are philosophical questions, as I explain in When Harry Became Sally.

While medical science does not answer philosophical questions, every medical practitioner has a philosophical worldview, explicit or not. Some doctors may regard feelings and beliefs that are disconnected from reality as a part of normal human functioning and not a source of concern unless they cause distress. Other doctors will regard those feelings and beliefs as dysfunctional in themselves, even if the patient does not find them distressing, because they indicate a defect in mental processes. But the assumptions made by this or that psychiatrist for purposes of diagnosis and treatment cannot settle the philosophical questions: Is it good or bad or neutral to harbor feelings and beliefs that are at odds with reality? Should we accept them as the last word, or try to understand their causes and correct them, or at least mitigate their effects?

While the current findings of medical science, as shown above, reveal poor psychosocial outcomes for people who have had sex-reassignment therapies, that conclusion should not be where we stop. We must also look deeper for philosophical wisdom, starting with some basic truths about human well-being and healthy functioning. We should begin by recognizing that sex reassignment is physically impossible. Our minds and senses function properly when they reveal reality to us and lead us to knowledge of truth. And we flourish as human beings when we embrace the truth and live in accordance with it. A person might find some emotional relief in embracing a falsehood, but doing so would not make him or her objectively better off. Living by a falsehood keeps us from flourishing fully, whether or not it also causes distress.

This philosophical view of human well-being is the foundation of a sound medical practice. Dr. Michelle Cretella, the president of the American College of Pediatricians—a group of doctors who formed their own professional guild in response to the politicization of the American Academy of Pediatrics—emphasizes that mental health care should be guided by norms grounded in reality, including the reality of the bodily self. “The norm for human development is for one’s thoughts to align with physical reality, and for one’s gender identity to align with one’s biologic sex,” she says. For human beings to flourish, they need to feel comfortable in their own bodies, readily identify with their sex, and believe that they are who they actually are. For children especially, normal development and functioning require accepting their physical being and understanding their embodied selves as male or female.

Unfortunately, many professionals now view health care—including mental health care—primarily as a means of fulfilling patients’ desires, whatever those are. In the words of Leon Kass, a professor emeritus at the University of Chicago, today a doctor is often seen as nothing more than “a highly competent hired syringe”:

The implicit (and sometimes explicit) model of the doctor-patient relationship is one of contract: the physician—a highly competent hired syringe, as it were—sells his services on demand, restrained only by the law (though he is free to refuse his services if the patient is unwilling or unable to meet his fee). Here’s the deal: for the patient, autonomy and service for the doctor, money, graced by the pleasure of giving the patient what he wants. If a patient wants to fix her nose or change his gender, determine the sex of unborn children, or take euphoriant drugs just for kicks, the physician can and will go to work—provided that the price is right and that the contract is explicit about what happens if the customer isn’t satisfied.

This modern vision of medicine and medical professionals gets it wrong, says Dr. Kass. Professionals ought to profess their devotion to the purposes and ideals they serve. Teachers should be devoted to learning, lawyers to justice, clergy to things divine, and physicians to “healing the sick, looking up to health and wholeness.” Healing is “the central core of medicine,” Kass writes “to heal, to make whole, is the doctor’s primary business.”

To provide the best possible care, serving the patient’s medical interests, requires an understanding of human wholeness and well-being. Mental health care must be guided by a sound concept of human flourishing. The minimal standard of care should begin with a standard of normality. Dr. Cretella explains how this standard applies to mental health:

One of the chief functions of the brain is to perceive physical reality. Thoughts that are in accordance with physical reality are normal. Thoughts that deviate from physical reality are abnormal—as well as potentially harmful to the individual or to others. This is true whether or not the individual who possesses the abnormal thoughts feels distress.

Our brains and senses are designed to bring us into contact with reality, connecting us with the outside world and with the reality of ourselves. Thoughts that disguise or distort reality are misguided—and can cause harm. In When Harry Became Sally, I argue that we need to do a better job of helping people who face these struggles.

The Quantity of the Hormones Make the Differences in Secondary Sex Characteristics

The obvious physical differences between the sexes are influenced by the quantity of androgens and estrogens, two chemicals from the steroid family of chemicals, released into our bloodstream. The biggest differences occur during the development of our secondary sex characteristics beginning at puberty. We know what they are and I will not go into any details about them here.

All the sex hormones in men and women originate from acetate and cholesterol molecules present in their bloodstream. The estrogens present in both sexes, more so in women than in men, are produced from the chemical breakdown of testosterone which is also present in the blood of both sexes. In case you didn&apost know testosterone is produced in both the testis and ovaries because the testis in the human male were once ovaries during fetal development until a chemical in the male body triggers the sequence to cause them to descend to the lower level into the scrotum to become the testis.

The testis make about 7 mg of testosterone a day and 1.75 mg of it is converted to small amounts of estradiol present in the blood of men while the ovaries in women only makes about 0.3 mg of testosterone and a little more than 0.15 mg of that is converted to estradiol. As we can see here it is the ratio of testosterone to estradiol and the potency of the two hormones that make the big differences between the sexes. Estrogens are 1000 times more potent than testosterone. The ratio of the amount of testosterone to estradiol found in men is 3 to 1 while the ratio of these two hormones in women is 1 to 1. Also, men make about 20 times more testosterone than women but the amount of testosterone converted to estrogens in women is 200 times more than men. It doesn&apost take much of either of these hormones to change the physical appearance of each sex to its opposite appearance.

Effect of Testosterone on the Male Body

Sex cells!

There is now a small international group of scientists racing to recreate the mouse formula and reprogram human iPS cells into sperm and egg cells.

One of the key players is Amander Clark, a stem cell biologist at UCLA. On a Friday afternoon, she walks me through her open lab area and introduces Di Chen, a postdoctoral fellow from China who’s working on creating artificial gametes. We enter a small room with a microscope, a refrigerator incubator, and a biosafety cabinet where students work with iPS cells. Chen invites me to peer down the microscope and shows off a colony of fresh iPS cells. They look like a large amoeba.

Getting cells like these to become viable eggs or sperm requires six major steps, Clark says. All of them have been accomplished in a mouse, but doing it in a human will be no easy feat. (In 2016, scientists reported that they had turned human skin cells into sperm cells, a development that Clark calls “interesting — but no one has repeated it yet.”) And no one has yet made an artificial human egg.

Clark’s group and other labs are essentially stuck on step three. After the steps in which a cell from the body is turned into an iPS cell, the third step is to coax it into an early precursor of a germ cell. For the work in mice, one Japanese researcher, Katsuhiko Hayashi, combined a precursor cell with cells from embryonic ovaries — ovaries at the very beginning of development — which were taken from a different mouse at day 12 in its gestation. This eventually formed an artificial ovary that produced a cell that underwent sex-specific differentiation (step four) and meiosis (step five), and became a gamete (step six).

Other researchers, Azim Surani at Cambridge and Jacob Hanna at the Weizmann Institute of Science in Israel, have gotten to step three with both human embryonic stem cells and iPS cells, turning them into precursors that can give rise to either eggs or sperm. Surani’s former student Mitinori Saitou, now at Kyoto University, also accomplished this feat.

It’s an impressive achievement: they’ve made something that normally begins to develop around day 17 of gestation in a human embryo. But the next step, growing these precursor cells into mature eggs and sperm, is “a very, very huge challenge,” Surani says. It will require scientists to recreate a process that takes almost a year in natural human development. And in humans they can’t take the shortcut used in mice, taking embryonic ovary cells from a different mouse.

At UCLA, Clark refers to the next three steps needed to get to a human artificial gamete as “the maturation bottleneck.”

Those amoeba-like iPS cells that Chen showed me are sitting in a dish that he lifts off the microscope and carries to the biosafety cabinet. There he separates the cells into a new dish, and adds a liquid with proteins and other ingredients to help the cells grow. He puts the cells into an incubator for one day then he’ll collect the cells again and add more ingredients. After around four days, the cells ideally will have grown into a ball that is around the size of a grain of sand, visible to the naked eye. This ball contains the precursors to a gamete. Clark’s lab and other international teams are studying it to understand its properties, with the hope that it will offer clues to getting all the way to step six — an artificial human gamete.

“I do think we’re less than 10 years away from making research-grade gametes,” she says. Commercializing the technology would take longer, and no one can really predict how much so — or what it would possibly cost.

Even then, same-sex reproduction will face one more biological hurdle: scientists would need to somehow make a cell derived from a woman, who has two X chromosomes, into a sperm cell with one X and one Y chromosome, and do the reverse, turning an XY male cell into an XX female egg cell. Whether both steps are feasible has been debated for at least a decade. Ten years ago, the Hinxton Group, an international consortium on stem cells, ethics, and law, predicted that making sperm from female cells would be “difficult, or even impossible.” But gene editing and various cellular-engineering technologies might be increasing the likelihood of a workaround. In 2015, two British researchers reported that women could “in theory have offspring together” by injecting genetic material from one partner into an egg from the other. With this method, the children would all be girls, “as there would be no Y chromosomes involved.”

Yet another possibility: a single woman might even be able to reproduce by herself in a human version of parthenogenesis, which means “virgin birth.” It could be the feminist version of the goddess Athena springing from Zeus’s head.

A complex mechanism

So will these rules apply in Rio? This is by no means certain since Indian sprinter Dutee Chand, who was diagnosed as hyperandrogenic following gender testing and forced to withdraw from the 2014 Commonwealth Games, brought her case before the Court of Arbitration for Sport (CAS). “At the request of this body, the International Association of Athletics Federations (IAAF) decided to suspend the regulations governing hormonal tests for two years. And the IOC is known to rigorously adhere to the positions of the IAAF,” notes Anaïs Bohuon, senior lecturer at the UFR STAPS at Paris Sud University. “Many observers question whether testosterone levels can be used to set the dividing line between male and female gender and as a basis for requiring that female athletes with hyperandrogenism must ″normalize″ their hormone levels.1 Dutee Chand, who feels she is a woman in all respects and has no desire to compete with male athletes, has unusually high testosterone levels that occur endogenously and without doping. Why then should a natural advantage comparable with that of large feet in swimmers or a high waist in jumpers be labeled as non-femininity?”

Intersex people Fermer People in whom male and female sexual characteristics coexist and who do not appear to belong unequivocally to one gender or the other. Numerous types of intersex conditions exist, such as chromosomal, gonadic, hormonal, etc. such as Chand are at the same time a source of unease for sporting authorities and a source of interest for biologists. Intersex traits, which are described in numerous mammals,2 appear to occur in between 1% and 2% of humans at birth. It is in fact the extreme complexity of the mechanisms involved in determination of biological gender that inevitably causes wrong notes.

This is why millions of individuals do not conform to the two gender types that characterize the immense majority of humans, namely the female type (two X chromosomes, ovaries, anatomical features favoring pregnancy and fetal development, breasts, and so on) and the male type (one X and one Y chromosome, a penis and testicles, internal ducts for the transportation of urine and sperm, etc.).

The diversity of forms of sexual development and the atypical types that occur are striking, whether of chromosomal, hormonal or environmental origin (caused by chemical products that disturb the endocrine system or by drugs taken during pregnancy, for instance). “The most extreme signs of sexual development disorders are those known as ‘sex inversions:’ ‘XY’ women with undeveloped testicles, as well as a vagina and a clitoris, and ‘XX men’ with testicles and a penis,” explains Francis Poulat, of the IGH in Montpellier.3 “In all recorded cases, these people are sterile. Furthermore, there is a strong risk of tumors (gonadoblastomas) developing in their gonads (ovaries and testicles). In addition to these examples, there are many other intermediate phenotypes in which both male and female sexual characteristics coexist in the same individual. Thus, XX babies with congenital adrenal hyperplasia (androgenic hyperproduction) are born with female reproductive organs and masculinized external genitalia (a hypertrophied clitoris resembling a small penis, fusion of the labia majora covering the vaginal entrance).”

Sex matters

Medicine has long worked on the assumption that women are essentially men with boobs and tubes – and so ‘women’s health’ became a term associated with the reproductive organs. It was only at the dawn of the 21st Century, with the emergence of evidence that women were experiencing heart attacks entirely differently from men, that the old ‘bikini medicine’ outlook began to be seriously challenged.

Heart researchers found that all those supposedly ‘classic’ symptoms – a tight pain in the chest, shooting pains down the arm, dizziness – were actually male symptoms. Women experience other signs such as shortness of breath, fatigue, nausea, and pain in the jaw or back. Yet these symptoms, which may be down to different patterns of obstruction in women’s coronary arteries, were not in the research literature, and were not being recognised by doctors. Women were dying of heart attacks as a result.

In the two decades since, a cascade of evidence has emerged indicating the deep-seated differences in male and female biology, and the need for different approaches to diagnosis and treatment.

For example, women have a faster and stronger immune response than men (so men are significantly more likely to die of infectious diseases), but women are more likely to have autoimmune diseases such as rheumatoid arthritis. Women’s and men’s metabolism, experiences of pain, and likelihood of developing Alzheimer’s disease are all different.

Here, it’s worth pointing out that sex and gender have different meanings, but are closely linked. ‘Sex’ refers to the biological differences between males and females. ‘Gender’ refers to a person’s characteristics or identity as shaped by society and the environment as well as biology. Gender medicine embraces both meanings, considering how women’s environment also affects their health and the way they are treated.

The differences between the sexes begin before birth, with male and female sex hormones such as testosterone and oestrogen helping mould brain and organ development from the embryo onwards. “Women experience constant fluctuations in hormones through every stage of life, which is an important difference from men, and has major implications for their health,” says Prof Alexandra Kautzky-Willer, head of the Gender Medicine Unit at the Medical University of Vienna.

The differences come right down to the sub-cellular level. Every cell, male or female, contains around 20,000 genes. Although these genes are virtually identical between men and women, research published by Israel’s Weizmann Institute of Science in 2017 found that around a third of them are activated (‘expressed’) differently in men and women. For example, the researchers found that the highly expressed genes in men’s skin were related to body hair growth. In all, there are an enormous number of factors at play.

“Gender health differences are the result of differences in genetic makeup, hormones, epigenetics – the effects of the environment on gene expression – and social factors,” says Kautzky-Willer.

Kautzky-Willer’s research specialises in diabetes, and she has found that men are more vulnerable to the condition later in life if their mothers endured hardship during pregnancy. She is also investigating whether separate blood tests are needed for men and women to diagnose diabetes and heart attacks. On the basis of new discoveries about differences in male and female blood chemistry, she is seeing an increasingly compelling argument that they are.

“There probably need to be different cut-offs or even different biomarkers for the same diseases,” she says. “Currently, to diagnose diabetes, you do an average blood glucose reading – HbA1c – plus a fasting glucose blood test. But we now know that women usually have lower fasting glucose and HbA1c readings than men, and you’re more likely to find women at risk if you additionally do an oral glucose tolerance test.”

By the Numbers

114,000 -- The number of same-sex couples who are raising children in the United States.

24% -- Amount of female couples who are raising children.

8% -- Amount of male couples who are raising children.

Find more articles, browse back issues, and read the current issue of WebMD Magazine.


Amanda Adeleye, MD, assistant professor of obstetrics and gynecology reproductive endocrinologist, University of Chicago Medicine, Chicago.

ASRM: “Is In Vitro Fertilization Expensive?”

Fertility and Sterility: “Lesbian, gay, bisexual, transgender content on reproductive endocrinology and infertility clinic websites,” “Recommendations for practices utilizing gestational carriers: an ASRM Practice Committee guideline.”

Jennifer Eaton, MD, division director of reproductive endocrinology and infertility, Brown University Medical School director of the Women & Infants’ Fertility Center, Providence, RI.

Mark Leondires, MD, founder and medical director, Reproductive Medicine Associates (RMA) of Connecticut, Norwalk, CT.

Mayo Clinic: “Intrauterine insemination (IUI).”

National Conference of State Legislatures: “State Laws Related to Insurance Coverage for Infertility Treatment.”

Planned Parenthood: “What is IUI?”

Suneeta Senapati, MD, assistant professor of obstetrics and gynecology, Hospital of the University of Pennsylvania director of third-party reproduction, Penn Fertility Care, Philadelphia.

The Sperm Bank of California: “How Much Does It Cost?”

UCLA School of Law Williams Institute: “How Many Same-Sex Couples in the US are Raising Children?”

Female Hormones

The control of reproduction in females is more complex. The female reproductive cycle is divided into the ovarian cycle and the menstrual cycle. The ovarian cycle governs the preparation of endocrine tissues and release of eggs, while the menstrual cycle governs the preparation and maintenance of the uterine lining (Figure 13.17). These cycles are coordinated over a 22–32 day cycle, with an average length of 28 days.

As with the male, the GnRH from the hypothalamus causes the release of the hormones FSH and LH from the anterior pituitary. In addition, estrogen and progesterone are released from the developing follicles. As with testosterone in males, estrogen is responsible for the secondary sexual characteristics of females. These include breast development, flaring of the hips, and a shorter period for bone growth.

Surrogate Motherhood

The most common form of surrogacy involves inseminating the surrogate with the husband's sperm--generally because the wife cannot carry a child through pregnancy. Such an arrangement should be avoided because a donor egg is involved, as explained above. Even when a donor egg is not involved--e.g., when the husband's sperm and wife's egg are joined in vitro--the bonding problems discussed below generally make such an agreement unwise. Particularly problematic are commercial arrangements in which surrogates receive payment for producing a child beyond expenses they incur. Like the selling of organs, such arrangements wrongly commercialize the body. In fact, financial contracts essentially entail the purchasing of the baby and imply an unacceptable form of ownership of human beings. Less problematic are altruistic surrogacies such as rescue surrogacies where a woman acts to save an embryo that would otherwise be destroyed.

UPDATE: A response to io9’s piece. (Here’s a direct link to this bit)

At io9, Annalee Newitz has written an interesting piece criticising much of the coverage of this story, including this post, and specifically the use of the term “female penis”. I disagree with many of her points and stand by the use of the term.

But first, to clarify, I absolutely agree with Newitz that cheap dick jokes are doing the topic a disservice, which is why you won’t find any here. The tone is as deadpan as I can muster—the only sniggering is reserved for the part of the study where one mating pair gets pulled apart and the male is accidentally bisected.

As to the other parts of Newitz’s critique, she repeatedly says that “female penis” is an inaccurate term that is “anthropomorphizing” Neotrogla’s anatomy—one should call the organ a “gynosome” (which I also do). I don’t agree that gynosome is accurate, while penis is not. As Diane Kelly, who studies penises points out: “As a technical term, a penis is a reproductive structure that transfers gametes from one member of a mating pair to another.” Which is exactly what is happening here.

Newitz points to differences. “When was the last time you found a penis that grew spines, absorbed nutrients, remained erect for 75 hours, or allowed its owner to get pregnant?” Actually spines are pretty common long sexual bouts are pretty common and the gynosome doesn’t absorb nutrients—it collects sperm packets that contain nutrients, which the animal then eats in the normal way. The key difference is that rather than delivering sperm, it collects it—as I stated right up top. And the only reason we think of penises as sending sex cells in that direction is that we never knew any other set-up could occur. Now we do, which either forces us to introduce a new term and demand that it be used, or to expand the bounds of our old term. I prefer the latter. I’m generally a lumper, rather than a splitter.

The gynosome is very much like a penis in both form and function. The authors highlight the differences by giving it its own specific name. But they also acknowledge its similarities to what we typically think of as penises by describing the organ as such, both in the title of their paper—“Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect”—and throughout its text. They don’t get any special privilege because of their authorship, of course—but I’m pointing out that you can either look at this discovery through the lens of difference or similarity. And similarities are actually critical here because evolution crafts organs that are convergently similar—though different in the details—thanks to similar selection pressures.

In fact, there is a long tradition in anatomy of describing organs with almost metaphorical names. A snail’s foot is not remotely the same as a human’s foot, but they’re both muscular locomotive organs that are kinda on the bottom of the body. We call them both feet. An octopus radula is not a human tongue, but they’re both mobile things inside the mouth that perform feeding functions, so we call them both tongues. “Eye” gets used to refer to all manner of light-detecting organs regardless of huge differences in their anatomy, evolutionary history, physiology, because they all share the common theme of detecting light. And in a similar vein, a Neotrogla penis/gynosome is not the same as a human penis but they’re both used during penetrative sex for the transfer of gametes. Other penetrating sexual organs, like the aedagus (insect) and gonopodium (fish) are also colloquially known as penises.

So, do we make a special case for sex-related terms? Newitz would say yes, because of the cultural and social baggage that “female penis” carries, in a way that “snail foot” does not. This is the strongest part of the argument, and the part that gives me pause.

But Newitz also argues that the term “erases one of the most beautiful things about life, which is its awe-inspiring diversity”, and there I disagree. The post above specifically references that diversity—not just in Neotrogla but other animals like hyenas and seahorses, and goes into detail about sexual selection. It ends deliberately with a quote about how the split between males and females comes down to sex cells, and everything else is labile. If that’s not celebrating the diversity of life, I don’t know what is. I don’t think that referring to Neotrogla’s female sex organ as a penis whitewashes that diversity. If anything, it forces us to realise that one of the traits we often link to a penis–that it lives on a male–isn’t a necessary truth. The usage expands what we know, rather than erases.

Watch the video: Ισότητα ανάμεσα στα δύο φύλα (June 2022).


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