Sex Biology and the Gish Gallop
Forrest Valkai, self-described science educator and activist, is known for debunking young earth creationism. But when it comes to the biology of sex, he uses their same fallacious tactics.
This rebuttal appears in Binary, a book published by the Paradox Institute.
Imagine you are trying to win a debate, and instead of presenting your argument with relevant evidence, you gather an incredible amount of irrelevant data against your opponent’s position.
This is common with young earth creationists, who believe that the earth was created 6,000 years ago. To try and validate their beliefs, young earth creationists dump an incredible number of arguments one after the other onto the opponent, from the idea that the light coming from other stars was created in transit to make the appearance of age to the idea that radiometric dating and other objective methods of dating rocks and fossils are based on a host of incorrect assumptions (Peppe & Deino 2013). Some of these arguments seem complex (and they might be), yet they are all irrelevant, misinterpretations of the evidence, or just complete fabrications. The key is that they all take advantage of people’s ignorance.
This is known as the Gish gallop. It is a fallacy often found in pseudoscience, where you attempt to drown your opponent in a “flood of individually weak arguments” which take much energy to refute (Elsher). While it was and still is common with young earth creationists, the strategy is now being used by sex spectrum pseudoscientists.
The best example of this Gish gallop technique is “Sex and Sensibility,” a 30 minute video that argues male and female are unreliable categories. It is written and presented by evolutionary anthropology student Forrest Valkai. Practically every sentence is riddled with information about the biology of sex, from the simple to the complex. Some points are true, and others are complete misrepresentations. There are so many points of information that it would take hours to carefully respond to each one, something we painstakingly did, which you can find here.
Forrest’s argument strategy is not much different from that of young earth creationists. Ironic, considering he is best known for debunking none other than young earth creationists.
To try and overwhelm the viewer with irrelevant evidence, Forrest barrages the audience with biological information, showing the various genetics, anatomies, and behaviors between males and females in humans and across species. Using this information dump, he attempts to show that the two sexes are arbitrary. However, his argument relies on the constant conflation of diversity in genes, anatomy, and behavior with sexes. No well-studied biologist would argue that, for male and female to exist, they must have consistent genetic systems, anatomies, or behaviors across all species.
In biology, the two sexes are defined as the phenotypes that produce either the smaller gamete (sperm) or the larger gamete (eggs) [Lehtonen and Parker 2014]. They are universal across the plant and animal kingdoms, having evolved independently in nearly every lineage of multicellular species (Kirk 2006). Within this system of two, there is no constraint on the diversity of anatomy and behavior across species (Scharer 2017; Goymann, Brumm, and Kappeler 2022). This is the beauty of the binary.
Knowing this universal definition is enough to defeat Forrest’s Gish gallop, because it can be correctly applied to all of his examples on the biology of sex. As an educational tool, let’s analyze the examples he uses and show how they reinforce the two sexes. I’ve broken them into six categories:
1. Variation in sex allocation
2. Variation in gamete size
3. Variation in sex determination mechanisms
4. Variation in genetic networks
5. Variation in sex characteristics
6. Variation in sexual behavior
1. Variation in sex allocation
Sex allocation is the optimal allocation of male and female sexes to organisms, whether they are composed in the same individual or in separate individuals, and whether the proportion of males versus females is higher, lower, or equal (Scharer & Pen, 2013). The exact form of this allocation depends on the species and the environment. Forrest argues that the definition of sex is unreliable because of this diversity in sex allocation, that they can be composed in so many ways across species. He uses examples known as dioecious, monoecious, simultaneous hermaphroditism, and sequential hermaphroditism.
Dioecious
This applies to a male-female sexual system in plants where individual plants are either male or female (Muyle et al. 2021). This means that one plant will have all female flowers or all male flowers.
Monoecious
Forrest claims that monoecious refers to species with one sex. But this is wrong. Monoecious describes sexual systems in plants where a single plant has separate male and female flowers (de Jong et al 2008). It does not mean one sex. It means two sexes on one plant. In other words, the individual plant has two sexes. This is where he shows that he misunderstands the meaning of dioecious and monoecious. The suffix -ecious describes the arrangement of sexual organs. And so dio-ecious means that the sexual organs are separated into two different individuals: females in one individual plant and males on another individual plant. Mono-ecious means separate male and female flowers on one plant.
Simultaneous hermaphroditism
Sexual systems where male and female exist in the same individual (an individual produces both sperm and eggs). This is common in plants, where an individual plant has individual flowers with male and female sexes, known as perfect flowers (Avise 2011). It is also seen in slugs, where an individual is both male and female at the same time.
Sequential hermaphroditism
Sexual systems where individuals switch sex depending on environmental circumstances. One example of this is the clownfish. They are all born male but can switch to female if there is an absence of a female in the environment. Thus, environmental triggers change the gonads from testes to ovaries, and they go from producing sperm to producing eggs (Casas et al. 2016).
Gonochorism
Sexual system in 95% of animal species, including humans, where individuals are either male or female through their entire life cycle (Muyle et al. 2021; Holub & Shackelford, 2021; Pla et al 2022).
Rather than showing the definition of the sexes is arbitrary, the diversity of sex allocation reveals the many ways the male and female sexes can be composed across species. The only way we can know whether an organism is either male or female, or male and female, or having switched from male to female, is whether they have a phenotype that produces sperm or eggs, or a phenotype that produces both, or a phenotype that has switched from producing sperm to producing eggs.
2. Variation in gamete size
Forrest claims that the gamete size definition of the sexes does not work because there are some male-female species that have many different gamete sizes and huge sperm, and species with no gamete size.
Species with many different gamete sizes
Drosophila bifurca, a species of fruit fly, has one size of egg and three different sizes of sperm. Forrest claims this species should have four sexes. Here’s the problem: he’s missing the fundamental meaning of “sexes.”
When biologists say the sexes are defined by the difference in gamete size, this is a shorthand for what the size differences represent. The size differences represent the two different reproductive contributions in reproduction (Lehtonen and Parker 2014; da Silva 2018; Lehtonen 2021). Males produce the gamete that holds far less to no resources for the future zygote, like a payload, which fertilizes the resource-heavy egg produced by the female.
When the sexes were first evolving over one billion years ago, there was an evolutionary trade-off between producing many small, fast gametes with little to no resources and producing few large, slow gametes with most of the resources for the zygote. I wrote a short literature review about how this evolution occurred here.
It does not matter whether there are many different sizes of sperm within a species or across species, nor does it matter whether there are many different sizes of egg. What matters is the contribution to reproduction (fertilizer or fertilized). The size difference between the male and female gametes is a great way to distinguish the sexes. In the fruit fly, the three different types of males can be defined as male because they all produce the sperm (the fertilizer).
Huge sperm!!
Forrest also claims that the gamete size distinction is violated because the same fruit fly produces sperm that is bigger than the female’s egg. The definition is not violated because this large sperm still fertilizes the egg and contributes little to no resources for the zygote. But why is the sperm bigger? It’s actually not bigger in volume; its head is still far smaller than the female’s egg. It’s just that the sperm is bigger in length. The male fruit fly has sperm that is 20 times the length of its body (Gardiner 2016). It’s a wound up ball of string that unravels inside the female reproductive tract. Biologists think its immense length is due to a process called runaway sexual selection, where male to male competition is so strong that sperm length was selected for by the female fruit flies as an indicator for male quality (Hill and Eisenberg 2016).
Longer sperm can also displace competitor sperm inside the female’s reproductive tract. Female fruit flies have large seminal receptacles, and so the energy cost for such long sperm is outweighed by the increased likelihood of fertilization with high quality sperm. Thus, it is the female reproductive tract that, in part, drove the shape of the male’s sperm. A similar situation happens in mammals where the longer the fallopian tube length is in the females of a given species, the larger the testes will be in the males (Anderson et al. 2006).
What variation in gamete size teaches us is the expected evolutionary diversity of sperm and eggs, not that the sex divide is arbitrary. Even with sperm and egg variation, we define them as sperm versus eggs by the two different functional contributions in reproduction.
Species with no gamete size
Forrest claims that the gamete size definition for the sexes is problematic because there are species who have male and female sexes but their gametes are the same size. The biology literature is very clear that these are not male and female sexes. They are called mating types (Perrin 2011). And such species have no sexes. This is called isogamy, a more ancient form of sexual reproduction often found in fungi or algae where gametes are the same size and form. They contribute equally to the zygote, as opposed to anisogamous (male-female) systems, where the cellular contribution to the zygote is unequal (Lehtonen, Kokko, and Parker 2016).
No biology literature claims that species with isogamy have male and female sexes, because sexes imply anisogamy (differently sized gametes) and mating types imply isogamy (same sized gametes) [Perrin 2011]. Isogamous gametes are only different on the molecular level, regulating which gametes can fuse with other gametes (Lehtonen and Parker 2014). There can be thousands or tens of thousands of gamete types in isogamous species. But no serious biologist claims these are sexes.
What isogamy teaches us is that there was a more ancient form of sexual reproduction before male and female originated, where gametes were not differentiated, but it does not call into question what male and female are, because isogamy is an entirely different sexual system.
3. Variation in sex determination mechanisms
Sex determination mechanisms are the regulatory systems, genetic and environmental, that determine sex, a technical term in biology for the development decision that triggers development down the male or female path in the womb (Eggers and Sinclair 2012). Sex determination mechanisms answer the mechanistic question of “how does an individual organism become a male or female?” (Beukeboom and Perrin, 2014). Across species, there are many systems for developing an individual’s sex (Bachtrog et al 2014). But Forrest claims this diversity in sex determination mechanisms shows sex is a spectrum. It does not. He uses two main examples.
Z-W system in birds
Unlike mammals, birds use the Z-W chromosomal system to determine sex, where ZZ birds develop into males, and ZW birds develop into females (Ioannidis et al. 2021). How do we know that the males are ZZ and the females are ZW? Could it be due to the biological definition of sex? The gamete type they contribute in reproduction?
Temperature sex determination
Reptiles are unique in the animal kingdom in that many species determine sex by the temperature at which their eggs incubate. In crocodiles, for instance, a certain range of temps trigger development into a male and another range triggers development into a female (Woodward and Murray 1993; Cornejo-Paramo et al. 2020).
The fact these species of reptile do not have sex chromosomes like us yet still develop as either male or female should tell us something about the difference between the mechanisms that determine sex (genes, temperature) and sex itself. If sex determination mechanisms were sex, then with temperature sex determination, each temperature value would be its own sex. Crocodiles would have infinite sexes! But they do not, because sex determination mechanisms are different from “sexes.”
4. Variation in genetic networks
Forrest also argues that, because there are so many genes and potential pathways for developing into a male or female, the two sexes cannot be reliably defined. This relies on conflating gene networks with sexes.
Everyone has the genes for making testes vs ovaries
Developing into a male or female in mammals requires a complex genetic network (Eggers and Sinclair 2012). As Forrest correctly points out, we technically have all the genes required for developing testes versus ovaries, because almost all of the genes involved in sex differentiation of the gonads are located on the autosomes (non sex chromosomes).
Some genes upregulate testes development, and other genes upregulate ovarian development. However, these genes are mutually antagonistic (Warr et al. 2012; Bashamboo et al. 2017; Witchel 2017). Their expression blocks the opposite-sex pathway from being expressed. This means that the male-making genes suppress female-making genes, and female-making genes suppress male-making genes.
For example, the SRY gene on the male Y chromosome upregulates SOX9, which differentiates the gonads into testes. The upregulation of SOX9 then inhibits female-making genes like WNT4 from being expressed. Females do not have the SRY gene, and so WNT4 is able to suppress SOX9, and ovaries develop (Leon et al. 2019). The purpose of this mutually antagonistic system is to ensure that both genetic networks do not activate at the same time, which would most often result in infertility (Warr et al. 2012).
Sex reversal in mice
Forrest uses experimental genetic tests on XX and XY mice, where researchers removed or added sex determining genes during embryonic development, resulting in a phenomenon called sex reversal (Ottolenghi et al. 2007; Eggers and Sinclair 2012). Sex reversal occurs when the sexual trajectory of the gonad is changed to the opposing pathway, switching the sexual phenotype of the organism from what is expected by their chromosomes (Weber and Capel 2018).
For example, XX mice with loss of WNT4 and FOXL2 developed into males, and XY female mice without the upregulation of SOX9 developed into females. This happened during the critical window of gonadal differentiation before it is fully established, not after (Weber and Capel 2018).
But how do we define the sex of these XX males and XY female mice? Answer: by their gonad/gamete type. Gametes differentiate according to the gonad tissue environment, not the chromosomes (McClaren et al 1995; Kocer et al. 2009). This is one reason why the sexes are defined by their role in reproduction, not by chromosomes. These examples of sex reversal in embryonic mice reveal the genetic mechanisms that control male and female development; they simply reinforce the two sexes.
Without genetic tests, we have no idea where we land
Forrest claims that without having your chromosomes tested or your genes analyzed, we have no idea where each of us land when it comes to our sex. This is not true. Karyotype studies have been conducted on tens of thousands of newborns across different decades, showing repeatedly that a person’s sexual phenotype (their reproductive system) matches with what is expected from their chromosomes (XX develops as a female; XY develops as a male) in more than 99% of births (Maeda et al 1991; Hamerton et al 1975; Nielsen & Sillesen 1975). Karyotypes outside of the typical XX and XY almost always result in infertility. And when people with these conditions are fertile, they produce sperm or eggs, never both and never a third gamete type. Thus, they are not additional sexes.
From genetic networks to atypical chromosome combinations, it is odd that Forrest thinks this variation proves male and female are arbitrary. On the contrary, these examples reinforce the meaning of male and female and reveal the mechanisms controlling their development.
5. Variation in sex characteristics
Forrest argues that another reason why the definition of sex is arbitrary is due to variation in sexual characteristics, such as genitalia or hormone levels, within humans and across species.
Are we born male or female?
Forrest claims that the idea we are born male or female is deeply flawed, and that there are hermaphroditic species that are simultaneous (they produce both sperm and eggs) or sequential (they start out as one sex and then switch).
First, in humans, we can accurately and easily observe sex at birth or even in utero by observing external genitalia, which accurately correlates to sex in more than 99.98% of births (Sax 2002; van Zoest et al. 2019). Second, what do hermaphroditic species have to do with humans, whose individuals are either male or female? And third, hermaphroditic species still involve only two sexes: male and female. It’s just that they are composed in a single individual, where individuals are both male and female or can switch due to environmental circumstances (Avise 2011; Scharer 2017).
In humans, there has been no documented case of a hermaphrodite. You will see medical literature sometimes using the term hermaphrodite applied to a human with a sex development disorder, but this is a misnomer. Since 2005, scientists have pushed to abandon the term hermaphrodite for humans, as it is “scientifically specious and clinically problematic” (Dreger et al. 2005). The definition of a hermaphrodite is to develop both male and female systems and to be able to reproduce as both sexes. No case has been identified in any human (Rosenfield 2018).
Hyenas and the pseudo-penis
Forrest uses the hyena, where its females have large, external genitalia like the males. This is supposed to confuse the viewer into thinking that the definition of sex is arbitrary. But the female hyena is female not because of the incorrect assumptions of biologists, but because she develops the large gamete reproductive strategy (a phenotype that produces eggs). Her ‘penis-like’ structure is actually a giant clitoris through which she urinates, copulates, and gives birth (Cunha et al. 2005). The female hyena shows the unique sex characteristics within females of other species.
Male lactation in a fruit bat
In a Malaysian fruit bat species known as the Dayak fruit bat, the males of the species have been observed to produce milk. But their mammary glands and nipples were not as large as females, and the amount of milk was only about a tenth of that produced by females. Males were not observed nursing young.
What’s the cause? One reason might be related to diet. These fruit bats eat fruit, but they also eat leaves that can contain estrogen-like compounds called phytoestrogens, which can stimulate milk production (Houghton 2023). So, this ability for the males to produce milk could serve no functional purpose. Even if they lactated just like females, it would not call into question which bat is male versus which is female.
Forrest makes the fundamental error of conflating variation in sex characteristics within humans and across species with sex itself. But sex characteristics evolved from the two sexes. They are byproducts of the two sexes, not examples beyond them.
6. Variation in sexual behavior
The last major category Forrest uses is variation in sexual behavior. He dumps on the viewer many cool and interesting examples of unique behavior across the animal kingdom and attempts to use this as evidence that the male-female distinction is arbitrary.
Seahorse reproduction
One major example Forrest uses is the unique reproductive biology of seahorses. Unlike mammals where the females gestate the young, male seahorses become “pregnant.” Except this pregnancy is not like mammals. The female seahorse deposits her eggs into the “brood pouch” of the male, where the eggs are fertilized by his sperm and incubated, protected, and provisioned (Zhang et al. 2018; Stolting and Wilson 2007). Even though the male seahorse “gestates” the young in his brood pouch, he is defined as male because he develops the phenotype that produces the sperm, just like every other male across species.
Dominant females and submissive males
Bonobos, historically called the pygmy chimpanzee, have dominant, socially aggressive females who form close bonds with each other to form social power over other group members. This goes against the stereotype of male aggression and domination over females, because there is evidence that these female bonds actually reduce male aggression patterns in the bonobo (Clay & Zuberbühler 2012). Despite their unique sexual behavior, we define the bonobos as male or female by the phenotypes that produce sperm or eggs.
Males building nests; females getting the food
In birds, it is common for the male to build the nest. There are many different techniques for nest building across avians; its ultimate purpose is to provide protection against environmental stress and predation which can also reduce offspring mortality and the need for parental care. Female birds have been sexually selected to seek out males with excellent nest building skills.
For example, in the common goby, whose males build nests underneath mussel shells by excavating a sand cavity, females prefer males with larger nests and solid sand ceilings (Pärssinen et al. 2019). We do not define these individuals as male or female based on their sexual behavior; we define them based on the biological definition of sex: the phenotype that produces sperm or eggs.
It is odd that Forrest thinks variation in sexual behavior across species is evidence that the male-female distinction is arbitrary. Instead of showing that male and female sexes are social constructs, the wide variation in sexual behavior reveals the beautiful diversity within males and females, something Forrest should appreciate if he truly wants to eliminate sex-based stereotypes and arbitrary social expectations for the two sexes.
Conflation of diversity with sexes
Ultimately, Forrest’s constant theme throughout his 30 minute video is the conflation of diversity within male and female with male and female themselves. He uses this treasure-trove of biological facts about the diversity of sex-related traits across species and within humans as evidence that male and female are somehow arbitrary, social constructs, and that the definition does not stand up to scrutiny.
But the biological definition of sexes is universal: it applies to every species with male-female sexes, regardless of within-species diversity in sexual behavior, sex characteristics, genetics, or sex allocation (Lehtonen and Parker, 2014; Scharer 2017). It’s not that every point Forrest utilizes is wrong; it’s that these many biological facts are used incorrectly, misrepresented, or are completely fabricated.
Forrest’s Gish gallop of irrelevant or misleading biological information is meant to confuse and muddy the viewer’s knowledge of male and female, not broaden or strengthen it. Just like the young earth creationists who rely on the reader’s ignorance of physics and cosmology to be effective, Forrest Valkai relies on the viewer’s ignorance of biology to be effective, which is no fault of their own. It just means they are being taken advantage of by someone who should know better.
If Forrest wants to be effective at communicating topics in biology while combating young earth creationism and its rampant denial of evolution, he should first confront his own.
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