Biology is all about food and sex: one lets you live long enough to do the other. However, sex isn’t the only means of reproducing. Billions of your cells reproduce asexually every day to replace all the ones that have died within you!
The basic processes of reproduction are the same among most of your cells. DNA divides and replicates before condensing into a more manageable form and the copies are split between two new cells identical to the original. Other than nerve cells, you are constantly reproducing new cells to replace the old ones that die. You may have heard the phrase “every seven years is a brand new you!”
This section will go into detail about sexual reproduction, since it’s how two humans make another one. At some point in our evolutionary history, a random mutation occurred to cause some cells of an organism to divide an extra time. The four daughter cells would then have half the DNA as the parent cell. We call these types of cells haploid.
This proved to be an advantageous adaptation as it allowed organisms of the same species to recombine their haploid cells in order to form a single cell with the proper amount of DNA. It might not sound too advantageous but the recombination allowed for a huge amount of possible genetic diversity. More diverse organisms have a better chance of finding new niches and surviving.
The reproductive system is the only one in which males and females differ, beyond small differences in development. Because of that we’ll have to tackle each separately. We’ll start with females.
Girls, before you are born, you have produced all the haploid cells that you will ever make in your ovaries; we call your haploid cells eggs. However, not all eggs are created equally.
When the sex cells divide, they do so unevenly. One daughter cell will take almost all the resources, leaving behind a shriveled sibling cell. Those two cells will divide again; the bigger one will again take most of the resources to leave one large egg and three very small haploid cells. The reason is to give the offspring the best possible chance at survival. Those individuals that produced the most resource filled eggs had a better chance that the offspring would survive, even if it meant fewer eggs.
Once a month, girls will release an egg from an ovary and it will travel down a tube and hang out in the uterus, waiting for some sperm to come fertilize it. If no sperm fertilize the egg, the egg and inner wall of the uterus will be removed out the opening to make room for a new wall and a new egg. Ladies, you know this as your period. You have one because those individuals who had younger cells lining their uterus were better able to produce viable offspring.
Guys, you’re a lot simpler! When you hit puberty, your testicles will descend for cooler temperatures and begin producing haploid cells; we call those sperm. Those cells will then develop caps and tails before they are ready for their journey.
Men, when you are sufficiently stimulated, you’ll launch over 20 million sperm cells along with a mixture of secretions with a higher pH. This is to protect the sperm from the slightly acidic environment of the vagina, a defense mechanism females have to protect against stuff getting in there.
The sperm will then experience the first competition of their young lives: get to the egg first. It’s a mad dash and only the fastest one will make it, another way to ensure the strongest offspring. Once the first sperm reaches the egg, the cap will dissolve and release enzymes to dig a hole in the egg.
The sperm will wiggle its way inside and the tail will pop off as the entire egg goes into “lock-down mode.” Once a sperm enters an egg, the egg’s membrane will not allow any other sperm to reach it and will actually push exterior sperm away. Those individuals that kept the right amount of DNA were better suited to survive. Preventing over fertilization is an advantageous adaptation.
The sperm and egg hybrid changes names and is now called a zygote until it replicates for the first time and we change the name again to an embryo. That embryo will develop a tube that burrows into the bloodstream of the mother and steals nutrients. That tube is called a placenta. Pregnancy is just another name for a very specific kind of parasite. It will continue to develop and grow, stealing nutrients from the mother until it’s born. In the last stage of development, the parasite finally starts to look like a human, at this point we call it a fetus. After about 9 months, the fetus comes out through the same opening that the sperm entered and we change the name once again to a baby. Hooray for names!
We are mammals and mammals adapted to allocate a ton of resources toward carrying their developing offspring within the mother. Other organisms like plants, fungi, fish, reptiles, etc. will produce a huge amount of possible offspring and only the strongest, of those that are born, will survive. Mammals’ allocation of resources to carry their developing offspring is yet another way to ensure the offspring have the best chance at survival.
Sex isn’t all about sperm meeting the eggs. If it was, a lot less of it would be happening around the world. Like I said before, life is about food and sex. You gain pleasure when you eat food because you’re extending your life. Sex also gives pleasure for extending your genetic line but the act of sex requires a lot of energy. Spending lots of energy is usually something that organisms try to avoid. To counteract this, sexually differentiated organs developed to stimulate pleasure. These organs are called the clitoris and head of the penis, with the male organ protruding for the purpose of insertion.
A pleasurable release throughout the brain and body, called an orgasm, offers even further encouragement to the Organism. This is a reward for risking your energy management to participate in your biological purpose. It also comes with a refractory period which is why it’s so easy to fall asleep right afterwards; you just used a lot energy, you might as well rest.
From a broader view, reproduction is the most important part of life. You are alive because your parents reproduced and your species will live on as long as humans continue to reproduce. It’s a mechanism that’s seen among many living things and it always works the same, though the details might differ.
Sex is NOT an unholy thing and it is very much a natural tendency to be curious and want to explore more. In our society, talking about sex is shunned but it is a part of you just like your ability to see and think. Learn about yourself, all of yourself, and you will be better for it.