Citations for the Gamete-Based Definition of Male and Female
A reference point for students, scientists, educators, and anyone interested in the biological understanding of “male” and “female.”
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Introduction
In recent years, a concerted effort has emerged to obscure the basic biology of male and female, often under the guise of inclusivity or rethinking science. Activists and many scholars now frequently portray sex as a spectrum or claim that being male or female depends on a complicated mosaic of traits—chromosomes, hormones, anatomy, identity—with gamete type presented as merely one of many “sex characteristics.” This framing is scientifically inaccurate.
In biology, the definition of male and female has never been arbitrary or culturally relative. It is grounded in the concept of anisogamy: the existence of two distinct types of gametes—sperm and ova. This fundamental reproductive asymmetry defines the two sexes across all sexually reproducing anisogamous species. An individual that has the function to produce small, motile gametes (sperm) is male; one that has the function to produce large, immobile gametes (ova) is female. This is not a social construct or a philosophical preference—it is a basic principle of evolutionary biology, established long before today’s cultural debates.
The historical and scientific record is clear: from the 19th century to the present day, biologists, medical professionals, philosophers of science, and evolutionary theorists have used gamete type as the defining criterion for sex. This document compiles citations from that record, providing a reference point for students, scientists, educators, and anyone interested in understanding what “male” and “female” mean in biological terms.
These citations span more than a century of scientific literature, showing that the gamete-based definition of sex is not a recent invention or a reactionary response, but a longstanding, fundamental biological principle. While sex roles and secondary sex characteristics can vary, the definition of the sexes does not: male and female are reproductive categories rooted in the type of gamete an individual has the function to produce.
This document is a work in progress. If you are aware of additional scholarly references—especially historical ones—that clearly depict the gametic definition of sex, please share them in the comments so I can continue to expand and improve this resource. I encourage readers to bookmark this page and return to it often as a reference in conversations, research, and advocacy.
Sincerely,
Colin Wright
CEO/Editor-In-Chief of Reality’s Last StandSCHOLARLY CITATIONS
19th Century
1888 – Charles Sedgwick Minot. “Sex,” in A Reference Handbook of the Medical Sciences Embracing the Entire Range of Scientific and Practical Medicine and Allied Science, Vol. 6, Alfred H. Buck (ed.) (New York: William Wood and Company), 436-438
As evolution continued hermaphroditism was replaced by a new differentiation, in consequence of which the individuals of a species were, some, capable of producing ova only; others of producing spermatozoa only. Individuals of the former kind we call females, of the latter males, and they are said to have sex.
20th Century
1903 – Robert Payne Bigelow. “Sex,” in A Reference Handbook of the Medical Sciences Embracing the Entire Range of Scientific and Practical Medicine and Allied Science, Vol. 7, Alfred H. Buck (ed.) (New York: William Wood and Company), 144-147
The ability to produce a macro- or microgamete constitutes the essential distinction of sex. The individual which produces the latter is said to be of the male sex, the individual producing the former is said to be of the female sex.
1911 – Encyclopedia Britannica (vol. 24), pp. 745-746.
An organism that contains the germinal tissue or mass of tissue known as the testis, and producing the sexual cells known as spermatozoa, is a male; an organism containing the tissue which produces ova is known as a female;…
1913 – Galloway, Thomas Walton. Biology of Sex for Parents and Teachers. (D. C Heath & Company), p 43
The egg is known as the female gamete, and the sperm is known as the male gamete. This difference of the gametes is the mark of sex.
1929 – Horatio Hackett Newman. Outlines of General Zoölogy (New York, The Macmillan Company), p. 448.
Any individual, then, is sexual if it produces gametes—ova or spermatozoa, or their equivalents. Thus we would be justified in calling any individual that produces ova a female, and one that produces spermatozoa a male. One that produces both kinds of gametes is a male-female or, more technically, a HERMAPHRODITE. Thus we may say that the PRIMARY SEXUAL CHARACTERS of individuals are the ova or the spermatozoa, and that maleness or femaleness is determined by the possession of one or other of these two types of gametes.
1949 – de Beauvoir, Simone. The Second Sex, translated by H.M. Parshley (New York: Vintage Books), 39
In the vast majority of species male and female individuals co-operate in reproduction. They are defined primarily as male and female by the gametes which they produce—sperms and eggs respectively.
1975 – Williams, George C. “Sex and Evolution.” Princeton University Press, pp. 127
The essential difference between the sexes is that females produce large immobile gametes and males produce small mobile ones.
1979 – Alexander, Richard D., and Gerald Borgia. “On the origin and basis of the male-female phenomenon.” Sexual Selection and Reproductive Competition in Insects, pp. 417-440.
Females are, by definition, those individuals in any gonochoristic (or dioecious) species which have specialized to produce a smaller number of larger and usually less motile gametes.
To say it another way, opposing selective forces operating before and after zygote formation may cause the evolution of two kinds of gametes, specifically, those that we call sperm and eggs; the same two kinds of selective forces may lead to the evolution of two kinds of individual organisms specialized to produce sperm and eggs, namely, males and females.
1986 – Dupré, John. “Sex, Gender, and Essence,” Midwest Studies in Philosophy 11(1): 441-457.
What it is to be male or female… is a property at a higher level of structural organization, that of producing relatively large, or small, gametes.
1987 – Kodric-Brown, Astrid, and James H. Brown. “Anisogamy, sexual selection, and the evolution and maintenance of sex.” Evolutionary Ecology 1, pp. 95-105.
The evolution of anisogamous gametes (small, mobile male gametes containing only genetic material, and large, relatively immobile female gametes containing both genetic material and resources for the developing offspring) not only established the fundamental basis for maleness and femaleness, it also led to an asymmetry between the sexes in the allocation of resources to mating and offspring.
1993 – Dupré, John. The Disorder of Things (Cambridge, MA: Harvard University Press)
What it is to be male or female… is a property at a much higher level of organization, that of producing relatively large or small gametes..
1994 – Charlesworth, Brian. “Evolutionary genetics: the nature and origin of mating types.” Current Biology 4.8, pp. 739-741.
The difference between male and female is manifested at the most fundamental level in the size and mobility of gametes: males produce many, small, motile gametes, whereas females produce a few, immotile gametes.
21st Century
2004 – Czárán, Tamás L., and Rolf F. Hoekstra. “Evolution of sexual asymmetry.” BMC Evolutionary Biology 4, pp. 1-12.
The primary difference between male and female is anisogamy, the differential size and mobility of gametes.
2009 – Futuyma, Douglas J. Evolution. 2nd ed., Sinauer Associates, Oxford University Press, pp. 389
Most sexually reproducing species have distinct male or female sexes, which are defined by a difference in the size of their gametes (ANISOGAMY).
2010 – Leonard, Janet L. “The evolution of sexes, anisogamy, and sexual systems.” The evolution of primary sexual characters in animals, Oxford University Press, Oxford, pp. 15-39.
The most fundamental and primary sexual character in animals is that of sex (=gender). In animals, the two sexes are defined by differences in the morphology and behavior of the two types of gametes and this anisogamy has been seen as the foundation and prerequisite of all sexual selection.
2011 – Parker, Geoff A. “The origin and maintenance of two sexes (anisogamy), and their gamete sizes by gamete competition.” The Evolution of Anisogamy: 17-74.
[I]n an anisogamous population, males produce microgametes and females produce macrogametes.
2011 – Lehtonen, Jussi, and Hanna Kokko. “Two roads to two sexes: unifying gamete competition and gamete limitation in a single model of anisogamy evolution.” Behavioral Ecology and Sociobiology 65: 445-459.
The two sexes, with the labels ‘male’ and ‘female’, only exist if gametes of two distinct sizes fuse to form a zygote. Why maleness and femaleness exists in the first place is a question of gamete size evolution: males by definition are the sex producing the small gametes in such anisogamous species.
2012 – Lehtonen, Jussi, Michael D. Jennions, and Hanna Kokko. “The many costs of sex.” Trends in Ecology & Evolution 27.3: 172-178.
“Anisogamous lineages produce two types of gamete. By definition, males produce the smaller type and females the larger type.”
2012 – Gamble, Tony, and David Zarkower. “Sex determination.” Current Biology 22.8: R257-R262.
Sexual reproduction in multicellular animals requires, at a minimum, male and female gametes. Indeed, these specialized haploid cells are how we define the sexes: in a given species individuals with big gametes are females and those with small gametes are males.
2013 – Roughgarden, Joan. Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press.
To a biologist, “male” means making small gametes and “female” means making large gametes. Period! By definition, the smaller of the two gametes is called a sperm, and the larger an egg. Beyond gamete size, biologists don’t recognize any other universal difference between male and female.
2014 – Beukeboom, Leo W., and Nicolas Perrin. The Evolution of Sex Determination. Oxford University Press.
“Male” and “female” functions will refer to the production of small or large gametes respectively (sperm and ova).
Individual gametophytes or sporophytes specializing strictly in one or the other sexual function will be referred to as males or females respectively…
2014 – Lehtonen, Jussi, and Geoff A. Parker. “Gamete competition, gamete limitation, and the evolution of the two sexes.” Molecular Human Reproduction 20.12: pp. 1161-1168.
…we must be clear about how the two sexes are defined in a broad sense: males are those individuals that produce the smaller gametes (e.g. sperm), while females are defined as those that produce the larger gametes.
2016 – Lehtonen, Jussi, Hanna Kokko, and Geoff A. Parker. “What do isogamous organisms teach us about sex and the two sexes?” Philosophical Transactions of the Royal Society B: Biological Sciences 371.1706: 20150532.
Separate sexes, gonochorism (in animals), dioecy (in plants): Systems in which the two sexes (males and females) are separate, and male individuals by definition produce small gametes and female individuals produce large gametes.
2018 – da Silva, J. (2018). “The evolution of sexes: A specific test of the disruptive selection theory.” Ecology and Evolution, 8, 207-219.
Gamete dimorphism, or anisogamy, in the extreme form of small motile sperm and large nonmotile eggs, or oogamy, defines sexes and is characteristic of plants and animals.
2021 – Franklin-Hall, Laura. “The animal sexes as historical explanatory kinds,” In: Dasgupta S, Dotan R, Weslake B (eds) Current Controversies in Philosophy of Science. Routledge, New York, pp 177–197
From a creature’s anatomy, to its behavior and genetics, biologists have uncovered no feature–save gamete size–perfectly distinctive of either sex.
2020 – Cotner, Sehoya, and Deena Wassenberg. The Evolution and Biology of Sex. University of Minnesota Libraries Publishing.
[S]exes can be distinguished, across the board, by gamete (or sex cell) size.
Scientists have created a definition of female that includes all the individuals that produce large gametes (eggs), those that produce small gametes (sperm) are male. Biologically, this large gamete/small gamete distinction between males and females is the only one that holds up well across many sexually reproducing species.
2021 – Lehtonen, Jussi. “The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness.” Cells 10.3: 573.
Biologically, the female sex is defined as the adult phenotype that produces the larger gametes in anisogamous systems.
Biologically, the male sex is defined as the adult phenotype that produces the smaller gametes in anisogamous systems.
2021 – Lehtonen, Jussi. “Gamete Size.” Encyclopedia of Evolutionary Psychological Science. Cham: Springer International Publishing. 3325-3328.
[I]n a system with two markedly different gamete sizes, we define females to be the sex that produces the larger gametes and vice-versa for males.
Gamete size is the defining feature of the male and female sexes.
2021 – Bhargava, Aditi, et al. “Considering sex as a biological variable in basic and clinical studies: an endocrine society scientific statement.” Endocrine Reviews 42.3: 219-258.
The classical biological definition of the 2 sexes is that females have ovaries and make larger female gametes (eggs), whereas males have testes and make smaller male gametes (sperm); the 2 gametes fertilize to form the zygote, which has the potential to become a new individual. The advantage of this simple definition is first that it can be applied universally to any species of sexually reproducing organism. Second, it is a bedrock concept of evolution, because selection of traits may differ in the 2 sexes. Thirdly, the definition can be extended to the ovaries and testes, and in this way the categories—female and male—can be applied also to individuals who have gonads but do not make gametes.
2021 – Griffiths, Paul. “What are biological sexes?” PhilSci Archive.
Male phenotypes evolved as part of a reproductive strategy focused on the production of large numbers of small gametes, such as human sperm. Female phenotypes evolved as part of a reproductive strategy focused on the production of smaller numbers of larger, highly-provisioned gametes, such as human eggs.
2023 – Hilton, Emma, and Colin Wright. “Two Sexes.” Sex and Gender. Routledge, pp. 16-34.
The majority of species, including humans, are composed of individual females and males, defined by reproductive role, describing their contribution of large, energy-rich gametes (like eggs) or small gametes (like sperm), respectively, to the next generation.
2023 – Goymann, Wolfgang, Henrik Brumm, and Peter M. Kappeler. “Biological sex is binary, even though there is a rainbow of sex roles: Denying biological sex is anthropocentric and promotes species chauvinism.” BioEssays 45.2, 2200173.
Biological sex is defined as a binary variable in every sexually reproducing plant and animal species. With a few exceptions, all sexually reproducing organisms generate exactly two types of gametes that are distinguished by their difference in size: females, by definition, produce large gametes (eggs) and males, by definition, produce small and usually motile gametes (sperm). This distinct dichotomy in the size of female and male gametes is termed “anisogamy” and refers to a fundamental principle in biology.
2023 – Byrne, Alex. Trouble with Gender (Cambridge, UK: Polity Press).
[F]emales are the ones who have advanced some distance down the developmental pathway that results in the production of large gametes. Similarly, males are the ones who have advanced some distance down the developmental pathway that results in the production of small gametes.
2023 – Rifkin, Maximiliana and Justin Garson. “Sex by Design,” Biology and Philosophy 38(13): 1-17
X is female if X has biological parts or processes that have the (proximal or distal) biological function of producing eggs.
X is male if X has biological parts or processes that have the (proximal or distal) biological function of producing sperm.
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Just a little footnote--also, in humans normal males have testes and penis, which cannot be manufactured through plastic surgery from female tissue. Normal females have the vagina, which cannot be manufactured from male tissue inverted and inserted in the pelvic floor through plastic surgery strategies. All sex trait modification surgeries are fraught with complications, some resulting in sepsis or necrosis and death. All sex organs are specific to either males or females as designated by chromosomes, determined at conception by the sperm (that is the little active one) that connects with the egg (that this the bigger less mobile one). No man can experience true female sexual sensations and no woman can experience true male sexual sensations. Vive la difference!
Up until 5 minutes ago I never would have dreamed that I would be bookmarking historical knowledge on the 2 sexes based on gametes. But these days I see so many posts on Facebook - in particular the one from a woke
biologist that talks about “chromosomal sex” and how we should believe people when they say who they are because biology is “complicated” and uses DSDs as so called proof. It’s frustrating and I can’t comment because .. well who’s going to listen to me. Thank you Colin and I wish more biologists would stand with you.