This paper will analyze some of the limitations of using male and female gender classifications when examining an animal’s biological sex and argue that these categories define gender through too narrow a lens and have little biological or scientific validity. The paper will explore gender variations within the animal world that challenge the strict definitions of male and female sex. It will demonstrate how the conventional notion of male and female among humans was imposed on the animal kingdom. However, it is here that this conventional grouping can easily be challenged. The paper will provide the ways in which reproduction can vary from the conventional model, such as genitalia variation, intersex, and biological and chromosomal expression that can also differ based on many environmental and hormonal factors.
Before discussing the specific examples that challenge the common model of sex and gender within the animal kingdom, we will look at how this model became the central method of classification. The study of human sex and gender is centered around the human dimorphic model. Humans are generally grouped into two phenotypic types: male and female (with some exceptions). Researchers brought this understanding of human biological sex into the study of sexuality in the animal kingdom (despite its primary applicability to primates) (Udry, 2000). Our understanding of human sexual dimorphism (male, female, xx or xy) has become the standard model for understanding sex and gender within the animal kingdom. Unfortunately, the human model falls apart when applying it to other species due to the variations of sex and gender among the animal kingdom. Some animals do not use x and y chromosomes to determine their sex biologically which is one of the key factors of human sexual dimorphism. Studies have shown how the influence of hormones in early developmental stages can drastically alter an animal’s sexual expression and gender in development and behavior, creating even more variety between the male and female genders (Barchunova, 2003).
Asexual and Homosexual Reproduction
With this understanding that the limited dimorphic model was brought to research in the animal kingdom, we will now examine some strong examples in animal reproduction that demonstrate a contradiction between the heterosexual reproduction model and what occurs in nature. One good example is the asexual reproduction of sharks. According to a journal article in Scientific Reports, a captive female shark in Australia who had been isolated from males for three years gave birth by switching from sexual reproduction to parthenogenesis (asexual reproduction). DNA testing proved this was a virgin birth, making the zebra shark the first to switch reproductive sexuality (Dudgeon, et al. 2017).
Fluidity of unisexual and asexual reproduction
Unisexual species also exist, thus challenging again the idea that there is only a male and female gender. One example of a unisexual species is the all-female whiptail lizards. These lizards reproduce through parthenogenic cloning, an ability that allows them to cross their own chromosomes to give birth (Cole, et al., 2016). Another animal, the Maine Flatworm changes its gender role for reproduction, sometimes reproducing asexually, and other times sexually. Maine Flatworms reproduce by engaging in penis fencing where one flatworm overpowers the other to impregnate the other. At the point the receiving flatworm becomes female. However, despite this mating ritual, flatworms can reproduce asexually as well (Ramm, 2017).
Pseudohermorphroditsm and Reproduction
Additionally, factors such as gender roles and sexual dimorphysical (genitalia) can vary from the perceived norm (male and female). Examples of unusual sexual dimorphism among the animal kingdom include instances of pseudohermorphroditsm (genitalia where appearance is opposite to the animal’s sex). According to an article in the Journal of Mammalogy, a 1988 study suggested that somewhere between 10- 20% of female brown bears have a penis-like structure in place of a vagina like the pseudopenis found on female hyenas. These intersex female bears can mate and give birth through the tip of their penis. Female pseudohermaphroditism may be caused in the fetus by the introduction of androgens of endogenous or exogenous origin causing an occurrence of genital abnormality fitting characteristics of both male and female (Cattet, 1988).
Pseudohermaphroditism in Humans
During the past 30 years, sexual ambiguity was an occurrence in parts on the Dominican Republic. Referred to by locals as “guevedoces” (Penis at 12), children would be born sexually ambiguous, later becoming men at puberty. Generally, these children were classified as girls due to the visible characteristics of their genitalia. However, this unique gender expression has been proven by research to be a genetic phenomenon, which became more common within a given area through genetic drift. This particular phenomenon is caused by an abnormality of the body’s production of estrogen which stabilizes itself when puberty occurs. Thus, influencing the formation of sexual organs in the affected person (Imperato-McGinley, Guerrero, Gautier, & Peterson, 1974; Marks, 2004; Money, 1976). Previously, it was believed that the sex of a child was established by the age of three years of age. As a result of this unique sex changing phenomenon, many of these men were raised as girls. More studies are needed to provide enlightenment on the psychological differences from this social differentiation.
Variation of Gender Roles
Seahorses demonstrate a complete gender role reversal. Instead of the male injecting his genetic material into the female, the opposite occurs, where the female injects her eggs into the male’s pouch where they are fertilized. A male pregnancy can last anywhere from 10 to 25 days (C. Kvarnemo, 2000).
Multiple Sexes
Like the brown bear, the Bluegill Sunfish also has extra genders. The Bluegill Sunfish has three different male genders, all which reach sexual maturity at different ages and vary in appearance. These fishes are classified as male even though there is a big difference in their physical appearance and differentiation in gender role. It seems that their differences in gender roles are biologically predetermined since their size, age of maturity, and behavioral pattern differ yet remain consistent (Ketterson, 2005). This consistent diversity in the male sex suggests a biological predisposition within the species which governs their distinctive sexual expression, development and features. A sexual tetramophic distinction is expressed in the Bluegill Sunfish that contradicts the standard dimorphic understanding of sexual expression. This demonstrates how male and female labels can be an over simplification.
Factors that Influence Sexual Expression
Finally, the most important reason why the use of just male and female categories when grouping animals by sex is not biologically or scientifically valid is revealed when looking at variations of sex chromosomes and inconsistent expression of sex determining chromosomes that exists in the animal kingdom. Also, the ability of some animals to change sex in adulthood makes the categories of male and female questionable. Examples of this include birds and butterflies which use W, Z and O (ZZ, ZO, WZ) for determining gender instead of X and Y(XX, XY). The W chromosome in these animals is usually associated with the development of female characteristics. When the W chromosome is absent, ZZ develops into males and ZO develops into females (Hake & O’Connor, 2008). Having a W chromosome to develop as a female is not even a necessity for some species.
Gender expression and environment,
In the absence of the W chromosome, a moth known as Talaeporia tubulosa uses the ambient temperature to control sex determination (Hake and O’Connor, 2008). This is true of most insects that can be influenced into developing into a female (instead of male) by the ambient temperature. The temperature (a determent in ideal breeding conditions) influences the presence of hormones which then influences chromosomal sexual expression, thus influencing the sex of these insects. Some species of reptiles’ gender can also be influenced in the same manner in fetal development.
Social status and gender
Along with chromosomes playing a role in determining the sex of an animal, other factors could also influence the developmental process. Clownfish gender, for instance is governed through social status. Despite consisting of both male and female genders which play a similar reproductive gender role as humans, Clownfish are significantly different biologically from humans regarding their sexual development. Clownfish are born with both sexual organs. Once Clownfish mature, their gender role in their community determines their sexual expression. Once the Alpha Female is gone from their school, the largest Alpha Male takes the place of the female. At this point the active genitalia switches, and the male becomes a functioning female who can reproduce with other males.
Chemicals that alter gender
Another example of environmentally influenced gender-switching is from a lab in Japan where an experiment was done on the Rana Rugosa frog. Different doses of testosterone were introduced to female frogs at early developmental stages. Because of the influence of the testosterone, female genitalia expression and sexual behavior changes occurred. More male behavioral patterns developed, as well as smaller female genitals. Depending on the amount of testosterone, a more male-like appearance developed in the female frogs. In extreme exposure, the sex of the Japanese frog Rana (R.) Rugosa even changed from female to male, demonstrating that sex determining chromosomes may not be the main factor in sexual development and determination in animals (Okie, et, al., 2016).
Conclusion
Although the terms male and female have been used widely to describe sex and gender in the animal kingdom, these terms are of limited use. The only situation where these terms are useful is in defining the two extreme ends on the sex and gender spectrum. This paper has cited many examples of animals that differ from the textbook definition of male and female. Using the term male and female has perhaps for many years blinkered our ability to even recognize different sex and gender expressions. It appears it is time to come up with new terms to better describe the variations in gender dynamics and roles in nature, as apposed to the essentialist idea of unchangeable ideal forms. From what has been observed in nature, it seems that various combinations of traits from both male and female sexes can be present in a species, while male and female sex remains the basis of the spectrum. Hopefully this would expand thinking when observing the animal kingdom and lead to new insights in this field.
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Things of Interest 