The Biological Underpinnings of Homosexuality

Image via Seattle Times

Existence of homosexuality has always been a matter of great confusion for heterosexuals. Many heterosexuals (I fell into this category in the not-so-distant past) believe that the sexual organ defines the sexual orientation.

This post is to question how it is possible to have different ‘wiring’ for orientation versus organs. This post is not about discussing the role of homosexuality in religion. There are a lot of things that happen in naturally, some of them are allowed by religion and some of them are forbidden; I am not getting into that debate here.

What I am discussing and clarifying here is that homosexuality is natural.

Let us take a layman’s look (‘layman’s’ because I myself do not have any background in genetics) at how genes get passed from parent to child.

Many of you must be aware that we have 23 pairs of chromosomes in our body. Here is a representation of our chromosome pair:

As you can see, the chromosome pair is comprised of two chromosomes. Using the diagram, the one on the left is from the father and the other is from the mother. Every chromosome contains genes (I have marked them in letters). It is the genes that decide your basic physiological and psychological under pinning, i.e. they primarily decide how you look and they provide the basis for your behavior.

In the above diagram A and A1, B and B1 and so on are called Allele. What it means is that A and A1 perform the same function but a different variation. For e.g. you might inherit gene for black hair from the father and say brown hair from the mother. Now this does not mean that you will have black-brown hair. This is so because there is a concept of dominant and recessive gene. Without going into a detailed discussion, let me just say that only one of the gene A or A1 is going to be active i.e. you are going to have either black hair or brown hair.

Something unusual happens while producing off springs. Recessive and dominant does not matter here. Biology (or god, take your pick) dictates that genes are going to be picked at random and create sperm or egg.

Here is another representation. First row has the parents, left side is father and right side is mother. Second row shows chromosome of an offspring where you can see both parents have randomly contributed to the genes from their own parents.

Let us assume that A1 is dominant to A2, B3 is dominant to B1, C is dominant to C2 and D2 is dominant to D. So the active genes are going to be A1 – B3 – C – D2

Coming back to our subject:

Which gene determines the sexual orientation? It appears that there is no single gene that makes this determination. Even in mice there are 54 genes that determine the sexual orientation and the sexual organs. In humans, chromosomes 7, 8 and 10 have received a lot of attention for this purpose.

In short what I am getting to is that (I do understand that I am being very speculative here) if a male receives a substantial part of his sexual genes from his maternal mother or paternal mother then is it not natural that the male will be attracted to another male? And vice-versa for females. Even if my interpretation is not correct — and most likely it is not — the above discussion should tell you that the whole business of inheriting genes is rather complex and not as simple as “if one has male organs then one is naturally attracted towards females and vice-versa”. What I can confidently say is that different wiring is expected and it must be serving some purpose since it survived the test of evolution.

Foot note: There is a special case of 23rd chromosome pair where one chromosome is passed from father to son (Y chromosome) and the other one is passed from mother (X chromosome). The difference is that there is no random selection of genes from the parent. Y chromosomes of grand-father – father – son – grandson (all males across generations) are identical (unless there is mutation). The same is true about the X chromosome that is passed from mother to daughter which is identical across generations.

The physical characteristics of the male sexual organs are determined by the SRY gene that resides exclusively on the Y chromosome. This is why we do not have half-men, half-woman in physical terms although there are cases in which some people are born with male and female organs. Incidentally, mutation of certain genes may cause this phenomenon; this is called 46, XX testicular disorder.

But what does all of this mean? Nobody chooses his or her genetic makeup. It’s natural. And homosexuality is an occurrence as natural as heterosexuality.

Chromosome images via


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    The Biological Underpinnings of Homosexuality