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Marriage Equality: Is ‘Biological Sex’ Only Defined by Chromosomes and Gametes?

Marriage Equality: Is ‘Biological Sex’ Only Defined by Chromosomes and Gametes?

Representative image. Photo: Interactive Content/Flickr CC BY SA 2.0

This is an edition of the Science & Gender column, which explores the intersection of these two realms in all their forms. Editions will be published once every six weeks.

On April 18 this year, while hearing solicitor general Tushar Mehta’s counter to the marriage equality petitions being argued in the Supreme Court, the five-judge bench headed by the Chief Justice of India (CJI) D.Y. Chandrachud astutely observed that “there is no absolute concept of a man or a woman at all[;] it cannot be the definition of what your genitals are[;] it is far more complex.”

A few days later, on April 21, Jawaharlal Nehru University biologist Anand Ranganathan, who doubles up as the consulting editor for the right-wing media platform Swarajya, retorted with a video on Twitter. In the video, which has amassed a massive 1.4 million views and has been liked by 20.3k Twitter users at the time of writing this report, Ranganathan finds the bench’s observation “deeply disturbing”.

According to him, the CJI is guilty of conflating “science with sociology” and “sex with gender”. He argues that a “biological man” is one who has XY chromosomes and produces sperm, and a “biological woman” is one who has XX chromosomes and produces eggs. Thus, he accuses the Supreme Court of participating in “anti-science quackery”.

In this edition of Science and Gender, The Wire Science investigates Ranganathan’s claims about “biological sex”.

Like table, like sex

In 2020, London School of Tropical Medicine and Hygiene professor Cicely Marston wrote that “the whole argument about gender and sex binaries is not an argument about science…it is an argument about classification and how we as a society choose to label people.”

In her blog post, Marston points out that “biological sex” is a label given to a set of characteristics that we, as a society, have decided to call so. As an example, Marston asks us to consider the label “table” given to a group of objects that show particular characteristics (for instance, having a certain number of legs). Yet, tables vary widely in their shape and size, in the number of legs they possess, and in the way they are used.

At times, this requires us to qualify the word “table”. For instance, a short table with four legs that people use to keep their coffee cups in a social gathering might be called a “coffee table”. On the other hand, a higher table with four legs that are used for people to work and study might be called a “study table”. 

That is, what we understand by the word “table” is not the same for everyone and what the word represents changes depending on the context in which it is used. 

In other words, the meaning of “table” is socially constructed. 

Importantly, recognising that the word “table” is socially constructed and might mean different things in different contexts does not, in any way, take away the reality of the table.

Representative image of a dining table. Photo: Jean van der Meulen/Pixabay

Using her deliberation on the word “table” as an analogy, Marston argues that the phrase “biological sex” is a “label used to describe a collection of indicators, biologies, and anatomies. Indicators (e.g. chromosomes, gametes) that have changed over time and with scientific discoveries.”

What are the “indicators” – that is, the set of properties/characteristics – that we call “biological sex”? More importantly, are they as simple as Ranganathan makes them sound – a pair of chromosomes, and a set of gametes?

In her 2012 book Sex/Gender: Biology in a Social World, biologist and gender studies scholar Anne Fausto-Sterling took a crack at explaining what sexologist and physician John Money called “layers of sex” in the 1950s. In Money’s paradigm, an individual’s encounter with their sex begins right after fertilisation, when the zygote – the product of the fusion between an egg and a sperm – acquires a particular chromosomal conformation. 

With respect to sex, the conformation of one particular pair of chromosomes appears to matter the most: the 23rd pair. For a large number of human beings, the conformation of this pair often tends to be XX or XY, while for a significant number of others, this conformation varies; it can be XXY or XO [The “O” stands for null, i.e., the person has only one chromosome in the chromosomal sex layer], or XYY, for example. This, in Fausto-Sterling’s words, is the “chromosomal sex layer”.

As one can see, even in the context of chromosomal composition, human “biological sex” is not binary.

Until about five weeks of embryonic development, the conformation of the 23rd pair of chromosomes matters little. When the foetus is about five weeks old, a few cells come together to form what is called the “bipotential primordium”. The bipotential primordium is neither male, nor female, but has the potential to be transformed into either testes, ovaries, or neither. Once the foetus has developed a bipotential primordium, it is said to have acquired an “indifferent foetal sex”.

At this point, the drama called “sex determination” begins. A gene in the Y chromosome – SRY (Sex Determining Region of Y) – is activated, raising the curtains for the bipotential primordium to transform into rudimentary testes. In its absence, the primordium develops into rudimentary ovaries. By 8-12 weeks of gestation, the foetus develops rudimentary gonads, and is said to have acquired a “differentiated foetal gonadal sex”.

The foetal gonads get to work quickly, sending hormones essential to foetal development surging through the body. At this point, the foetus acquires a “foetal hormonal sex”.

These hormones have different effects on the foetus. Notably, on the one hand, it helps in the development of the internal parts of the reproductive system (e.g. vas deferens, fallopian tubes, uterus, cervix, etc.), thus, granting the foetus an “internal reproductive sex”. On the other hand, it leads to the development of external genitalia in the foetus, at which stage the foetus is said to have a “genital sex”. 

Further, in a claim that has been contested, these hormones may also shape parts of the developing brain differently in foetuses of different sexes, thus granting the foetus an alleged “brain sex”.

By the time the foetus is born, it already has five sex layers. More get added as the newborn grows. For instance, at puberty, levels of the so-called “sex hormones” peak, leading to the layer of “pubertal hormonal sex”. As a result of these hormones, the teenager develops erotic sensations and desires – thus, acquiring a “pubertal erotic sex” – and sex-differentiated external and internal bodily features (i.e., a “pubertal morphological sex”).

From this discussion, two arguments become clear: one, “biological sex” is more complex than an individual’s chromosomal composition and the kind of gamete they produce. Two, what is considered an individual’s “biological sex” changes incrementally over time as the individual acquires new “layers of sex”.

Biological sex, therefore, is more than chromosomes and gametes. And, it is definitely not set in stone, even during an individual’s lifetime.

Also Read: A Pathway for the Supreme Court in Ensuring Marriage Equality

Fifty shades of (biological) sex

That biological sex is layered is one layer of complexity. That these layers of sex do not always fall in line with each other is another.

Consider a watercolour artist armed with three primary colours – red, blue and yellow. Now, the artist has an arduous task ahead – to create the colour brown. Here are the three ways the artist might go about it:

  1. They might first combine blue and yellow to make green, and then add red to the mix to produce brown.
  2. They might first combine blue and red to make a shade of purple, and then mix purple with yellow to make brown.
  3. Finally, they might begin by adding red to yellow to make orange, and then mix blue to make brown.

Thus, there are multiple processes that can take us to the same end product – the colour brown, in this case. Similarly, multiple processes can take us to the same indicators of biological sex.

Consider one indicator of the “female” biological sex: the external genitalia (what, in Money’s paradigm, is “genital sex”). Typically, such individuals are expected to have an XX chromosomal configuration and a uterus.

However, in certain cases, people who have an XY chromosomal configuration might show the same indicator. This is because such individuals possess ‘atypical’ forms of the “androgen receptor”, a protein required by the hormone testosterone to make its effects visible. 

(Testosterone is one of the hormones responsible for differentiating the bipotential foetal reproductive structures to their “male” forms.)

Since testosterone is unable to act in such individuals, – who are often clinically referred to as people with “Complete Androgen Insensitivity Syndrome” – they have “typical female external genitalia”, along with rudimentary and undescended testes. They also lack a uterus and do not menstruate.

The term “intersex” is used for people who are born with sex indicators that do not conform to the typical medical definitions of “male” or “female”. They may have chromosomal conformations other than XX or XY, or/and different anatomical and morphological variations. Estimates for the number of intersex people in the world vary widely, but the range is usually believed to be across 0.02%-1.7% of all live births.

Hence, not only is biological sex defined by more than an individual’s chromosomal composition or the gametes they produce, but it is also not a binary.

The X and Y chromosomes, also known as the sex chromosomes. Photo: Jonathan Bailey/National Human Genome Research Institute/National Institutes of Health/Flickr

8000 years of support for marriage equality?

At one point in the video, Ranganathan declares, “What’s beautiful, our 8000-year-old civilization has always supported homosexuals and transgenders [sic].”

While on the face of it, Ranganathan appears to support marriage equality (the video is peppered with other statements like “homosexuality is as natural as heterosexuality”, “gay rights are human rights”, etc.), his belief in his “8000 year-old-civilisation” (presumably, Hinduism) is perhaps unfounded.

Consider the ancient Hindu text Manusmriti. It prescribes the following “cleansing” ritual for men who have sex with men: “If a man has shed his semen in non-human females, in a man, in a menstruating woman, in something other than a vagina, or in water, he should carry out the ‘Painful Heating’ vow.” (Chapter 11, Verse 174)

Further, the sexual union of a man with a man is said to cause the “loss of caste”: “Causing an injury to a priest, smelling wine or things that are not to be smelled, crookedness, and sexual union with a man are traditionally said to cause loss of caste.” (Chapter 11, Verse 68)

In this text, not only is there no support for homosexuality, but homosexual relationships – especially between men – are punishable.


Ranganathan’s video, therefore, neither sheds light on the reality of biological sex nor does it point to any key fallacy in the Supreme Court’s verbal observations. On the contrary, it weaponises science, albeit with a veneer of benevolence. 

The Supreme Court is not indulging in “anti-science quackery”; in stark contrast, it is upholding what science tells us about “biological sex”.

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