eli5: How does the population ratio between women and men keep so equal? (A Different Approach)

Question

Hey! I’m wonderin that how does the population ratio is still more or less %50-50 (%49.5 female vs %50.5 male) even that the knowledge we know;

1- Men is being killed, and killed in past in wars.

2- Men is working on heavy-duty jobs that killed men.

3- We also know that the expected life span of a female is higher than men.

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So, there should be some imbalances, right?

Men dies in wars, in dangeroues jobs and has less life time.

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So, how does the ratio keep its balance?

In: Biology

Answer 1

Before we talk about death, let’s talk about birth, more specifically, genetics (what makes male and female).

The formation of a baby requires a female egg (which always has an X chromosome) and a male sperm (which could have either an X or a Y chromosome). You probably know that it takes an XY combination to make a male and an XX combination to make a female. So how is it that we know it should be about 50/50 male:female sperm? In very simple terms, the DNA in an egg and a sperm creates a cell with half the DNA of a standard human cell and when put together a fertilized egg has all the DNA needed to make a human (pretty cool actually).

When making the egg the female only has X chromosomes, so in oogenisis (the formation of the egg in a female) when the cells split up they only have x chromosomes to “choose” from, that’s where the first X comes from. For spermatogenesis (the formation of sperm in the male) each single cell that is used actually forms 4 sperm cells (long story short, 1 full cell splits into two full cells and each of those two cells split in half cells, aka sperm, making a total of 4). When you split the DNA into 2, one half will have an X chromosome and the other half will have a Y chromosome. This makes it a 50/50 chance of the sperm that reaches the egg will be male or female.

As far as death goes, I haven’t looked into the actual numbers so I can’t really say anything on that. But at this point in time the world is relatively peaceful (I know there are wars that are going on around the world, but nothing anywhere near the scale a world war, which would actually cause a percent decrease in the population). That being the case it would make sense to have a slightly higher percentage of woman in the world than man, given that they live longer.