Incels always whine about looks or economic problems for why they can't get sex, but one thing I never see mentioned is how the natural human sex ratio is biased towards males at birth.

This makes sense from an evolutionary perspective, as boys are more susceptible to disease then girls due to the Y chromosome, and since childhood mortality was so high, the population that survived to adulthood probably had a nearly 1:1 sex ratio (see Fisher's principle, if you want to understand why natural selection favors an equal ratio https://en.wikipedia.org/wiki/Fisher%27s_principle ). But now with contemporary medicine, childhood mortality is much lower, so more males are surviving to adulthood, and the sex ratio for young adults is skewed in favor of men.

But how skewed is it? According to Wikipedia, estimates are that the ratio is about 1.05 or 1.06 https://en.wikipedia.org/wiki/Human_sex_ratio . That does not sound like a lot, but those numbers do not give you an intuitive understanding of just how many 'extra males' there really are. If we take the lower estimate, a more intuitive ratio is 21 / 20, meaning that for every 21 males that are born there are only 20 females https://www.google.com/search?q=21+%2F+20 .

We can actually see this ratio showing up in national census data. Looking at the demographics of the United States https://en.wikipedia.org/wiki/Demographics_of_the_United_States , you can see that the sex ratio for the population aged 0 to 14 and 15 to 24 is almost 1.05 . This gap narrows with age, as the male mortality rate is higher overall, with the national sex ratio even biased towards females, but the fact remains that a large amount of incels are within the 15 to 24 age bracket or are a decade or so older, and within that range there are more males than females, and that this imbalance could be a major contributing factor as to why there are so many incels: there are not enough women to go around.