How Is Your Sex Determined?

At some point, I'm sure many of you have come across a list of famously non-relevant interview questions asked at Google. Questions like "How much would you charge to wash every window in Seattle?"—a seemingly silly question considering it never stops raining there.

Another question from the list goes like this: "Imagine a country where everyone only wants boys, so if a couple has a girl, they have another child. If they have a boy, they stop. What is the proportion of boys to girls in the country?" It's a challenging question with various debates over the answer, but most people tend to conclude that the ratio is a 50/50 mix of boys and girls.

But let's shift focus now and ask a different question: do you truly love sex?

Are there genetic or environmental factors that can influence this preference? And is the difference between genders really as straightforward as black and white, or should I say blue and pink?

As humans, we have 23 pairs of chromosomes, and 22 of these pairs are the same for both men and women. The 23rd pair determines our sex, where women have two X chromosomes, and men have an X and a Y chromosome, with the Y being much smaller than the X. The X chromosome carries over 2000 genes, while the Y has just 78. However, shortly after fertilization, one of the X genes in women nearly completely deactivates, so both genders end up with a similar number.

In the early weeks of fetal development, male and female embryos are fundamentally similar. It's only later that their genitals take separate paths, though they are more alike than we might realize. The gonads become either testes or ovaries, the phallus becomes either a penis or a clitoris (which actually extends a few inches but remains internal), and the labia and scrotum are quite similar, differing only in... let's say, origami.

Around the 16th week of pregnancy, or later, we can determine a baby's sex and realize whether we need to exchange the pink dresses we bought. This process of genital development reveals that it's possible for genitals not to fully develop in one direction since they begin as quite similar structures. Depending on the definition, a small percentage of people, between 0.1% and 1.7%, are born biologically "intersex," with their anatomy falling somewhere in between male and female.

Regarding genetic combinations, it's also possible to have XX and XY chromosomes. In extremely rare cases, the Y chromosome can even attach to one of the XX chromosomes. Many of these outcomes are rare because those individuals might face reproductive challenges, preventing certain characteristics from being passed on.

Now, let's explore how your cells initially determine your XX or XY combination. Do the sperm and egg arm wrestle for it? Can hanging a picture of Vin Diesel above the bed increase your chances of having a boy?

Currently, the global sex ratio is 107 boys for every 100 girls, and the gender is determined by the sperm. A man produces two different sperm cells: one containing an X chromosome and the other containing a Y chromosome. If the X sperm fertilizes the egg, you get a girl, and if it's the Y, it's a boy. As the X and Y sperm contain different amounts of genetic material, with the X being 1.03 times heavier than the Y, there are speculations that gravitational pressure during and after sex might influence the baby's gender, but this is not proven.

Many myths surround gender influence, such as the timing of ovulation during sex or the type of breakfast cereal you eat, but nothing reliable has ever been proven. The reason most species end up with a 1:1 sex ratio is attributed to Fisher's Principle, a natural balancing act where any tendency to produce more males is eventually counterbalanced by population dynamics.

It's fascinating to consider how environmental factors can alter the human sex ratio in a particular area. For instance, a report by Berkley professor Ralph Catalano suggested that ambient temperature could change the ratio, with a 1°C rise possibly resulting in 1 extra boy for every 1000 births. Additionally, after a war, the birth rate of males tends to increase, seemingly restoring balance.

Dr. Corry Gellatly proposes that the Fisher Principle may still play a role in these scenarios. If a man's family has more brothers than sisters, he's likely to produce more Y sperm, increasing the chances of having boys. When a war occurs and more men are sent to battle, families with more brothers might have a greater chance of having at least one son return alive, leading to a higher proportion of Y-sperm-biased offspring.

In the end, life can be boiled down to sperm and statistics. Regardless of a baby's sex, over their lifetime, they will produce a significant amount of waste, including about 600 large cans of garbage and over 10 million liters of wastewater.