Pedro de San Patricio
Gold Member
The origins of sex
Probably the easiest way to start is at the beginning. The first life forms were what we call "asexual". They reproduced (that is, made more of themselves) through non-sexual means, such as division. To imagine that, think of a cell pulling itself in opposite directions until it rips apart and becomes two brand new cells. That's not exactly what was going on, but it does illustrate the idea sufficiently for our purposes. This continued from the origin of life (which I may or may not get into in a follow up thread for the Creationists' sake) to approximately 2.1 billion years ago, when a new type of cell came about which reproduced in a sexual manner. Rather than dividing to create two new cells out of one old one, in this new method two cells would attach themselves to each other and combine genetic information to create a third cell with traits of both. This was useful because it enabled genetic diversification.
To understand why that's important, just think about two of the old single celled organisms trying to escape predation (which is a fancy word for "being eaten"). They're genetically identical so neither would be any faster in getting away. The new sexual method of reproduction allowed individuals to possess unique genetic information and so some would be faster in escaping than others and the faster ones would tend to survive to create new fast ones. This is something we call "natural selection". A population adapts to the challenges of its environment as the more adapted individuals pass along their genes and the less adapted ones fail to do so.
Why does any of that matter to us?
I'm hoping that this is making sense so far. I've never actually gotten the opportunity to give this talk before. Let's presume I am and continue. The reason all of the above applies to us as human beings is that we as animals are descended from those first sexually reproducing cells and reproduce through the same method - sex. Of course we don't do it the exact same way they did but the basic idea of joining genetic information hasn't changed. I may be getting a little ahead of myself though. As humans, we come in two sexes: male and female. You've probably noticed the differences between them up until now, but as I have no way of knowing what you personally know already I'm just going to explain them anyway.
The differences between the sexes
The primary differences come down to a set of organs unique to each sex. The male reproductive organs are the penis, which is a long shaft-like organ having down from the middle of the waist; two testicles, which are ball-shaped organs residing within a sack-like container hanging directly below the penis called the scrotum; and another organ within the torso called the prostate. The female reproductive organs are the vagina, which is a long tubular organ beginning at the hole called the vulva which is approximately where the penis is on the male body; the uterus, which is where the vagina leads and is divided into a lower area called the cervix and a main chamber; and two organs called the ovaries, which connect to the sides of the uterus by things called fallopian tubes. Two other important parts of the female body are called the breasts, which are the fatty organs hanging from the chest region. They aren't part of the reproductive tract itself but they do play a role after pregnancy which I'll explain in the relevant section.
Fertilization
You may be wondering why I explained this to you. That's okay. We're starting from a clean slate. Basically those organs - the penis, testicles, prostate, cervix, uterus, and ovaries - are how we combine the genetic information and raw materials which go into making babies. At periodic intervals the mature female body releases something called an "egg cell" into the uterus.The testicles and prostate create a fluid substance called semen, which is composed of things called "sperm cells" and various elements things like fructose in which those sperm cells "swim". This substance is introduced into the vagina by the insertion of the penis. It requires a significant, mutually pleasurable stimulation to release that substance. Once that substance has been released, it travels through her vagina and to her uterus where a sperm cell merges with the egg cell in a process called "fertilization" to create a zygote.
It feels good, so isn't that what it's for?
This was the common objection in the last thread so it may be a good idea to address it now. The problem with this line of reasoning is that it presumes that what you're using it for and why it exists must be the same thing. As explained above, the biological purpose of the act is to enable fertilization. It's true that it's pleasurable. The reason the pleasurable aspect evolved was to further encourage individuals to reproduce. Think about it. The more an individual enjoyed the act the more they would seek out opportunities to do it which would lead to more offspring also wired to enjoy it. Nature likes rewarding positive behaviors. (Note that I'm not actually saying that nature is a sentient being that physically pats people on the back. It's metaphorical. It's sad that I need to stress this, but we all know the shitstorm that would come from trusting people's reasoning abilities.)
Pregnancy 101
Continuing from fertilization, the zygote undergoes a process called cleavage in which it asexually reproduces (remember that concept from the first section?) to create new cells called "blastomeres". They continue to divide. At eight cells they form a structure called a "morula", which becomes a hollow call called a "blastula". The blastula further develops to become a "blastocyst". The blastocyst develops into an "embryo" and "placenta". The placenta is the organ which connects the embryo to the uterine wall. The embryo uses the nutrients obtained from the uterus to continue development and becomes called a fetus around nine weeks post-fertilization. Approximately nine months later that fetus is born and is known as an infant.
Wait, but that would mean that a fetus is alive...?
Well yeah. Any discussion of that fact beyond acknowledging it will cause a train wreck of a derail though. Let's just accept it and move on.
No. That's fucktarded. My women's studies professor said it's not alive until it's born!
MOVING ON...
Further reading
Hopefully you've found this informative despite its basic nature. It really is a fascinating subject. If you would like to learn more about it and get all the details then I highly recommend the links below.
Medical Embryology - Difficult Concepts of Early Development Explained Simply
Embryology
Evolution of Sex
Evolution of sex data
Scientists peek at the early evolution of sex chromosomes
Probably the easiest way to start is at the beginning. The first life forms were what we call "asexual". They reproduced (that is, made more of themselves) through non-sexual means, such as division. To imagine that, think of a cell pulling itself in opposite directions until it rips apart and becomes two brand new cells. That's not exactly what was going on, but it does illustrate the idea sufficiently for our purposes. This continued from the origin of life (which I may or may not get into in a follow up thread for the Creationists' sake) to approximately 2.1 billion years ago, when a new type of cell came about which reproduced in a sexual manner. Rather than dividing to create two new cells out of one old one, in this new method two cells would attach themselves to each other and combine genetic information to create a third cell with traits of both. This was useful because it enabled genetic diversification.
To understand why that's important, just think about two of the old single celled organisms trying to escape predation (which is a fancy word for "being eaten"). They're genetically identical so neither would be any faster in getting away. The new sexual method of reproduction allowed individuals to possess unique genetic information and so some would be faster in escaping than others and the faster ones would tend to survive to create new fast ones. This is something we call "natural selection". A population adapts to the challenges of its environment as the more adapted individuals pass along their genes and the less adapted ones fail to do so.
Why does any of that matter to us?
I'm hoping that this is making sense so far. I've never actually gotten the opportunity to give this talk before. Let's presume I am and continue. The reason all of the above applies to us as human beings is that we as animals are descended from those first sexually reproducing cells and reproduce through the same method - sex. Of course we don't do it the exact same way they did but the basic idea of joining genetic information hasn't changed. I may be getting a little ahead of myself though. As humans, we come in two sexes: male and female. You've probably noticed the differences between them up until now, but as I have no way of knowing what you personally know already I'm just going to explain them anyway.
The differences between the sexes
The primary differences come down to a set of organs unique to each sex. The male reproductive organs are the penis, which is a long shaft-like organ having down from the middle of the waist; two testicles, which are ball-shaped organs residing within a sack-like container hanging directly below the penis called the scrotum; and another organ within the torso called the prostate. The female reproductive organs are the vagina, which is a long tubular organ beginning at the hole called the vulva which is approximately where the penis is on the male body; the uterus, which is where the vagina leads and is divided into a lower area called the cervix and a main chamber; and two organs called the ovaries, which connect to the sides of the uterus by things called fallopian tubes. Two other important parts of the female body are called the breasts, which are the fatty organs hanging from the chest region. They aren't part of the reproductive tract itself but they do play a role after pregnancy which I'll explain in the relevant section.
Fertilization
You may be wondering why I explained this to you. That's okay. We're starting from a clean slate. Basically those organs - the penis, testicles, prostate, cervix, uterus, and ovaries - are how we combine the genetic information and raw materials which go into making babies. At periodic intervals the mature female body releases something called an "egg cell" into the uterus.The testicles and prostate create a fluid substance called semen, which is composed of things called "sperm cells" and various elements things like fructose in which those sperm cells "swim". This substance is introduced into the vagina by the insertion of the penis. It requires a significant, mutually pleasurable stimulation to release that substance. Once that substance has been released, it travels through her vagina and to her uterus where a sperm cell merges with the egg cell in a process called "fertilization" to create a zygote.
It feels good, so isn't that what it's for?
This was the common objection in the last thread so it may be a good idea to address it now. The problem with this line of reasoning is that it presumes that what you're using it for and why it exists must be the same thing. As explained above, the biological purpose of the act is to enable fertilization. It's true that it's pleasurable. The reason the pleasurable aspect evolved was to further encourage individuals to reproduce. Think about it. The more an individual enjoyed the act the more they would seek out opportunities to do it which would lead to more offspring also wired to enjoy it. Nature likes rewarding positive behaviors. (Note that I'm not actually saying that nature is a sentient being that physically pats people on the back. It's metaphorical. It's sad that I need to stress this, but we all know the shitstorm that would come from trusting people's reasoning abilities.)
Pregnancy 101
Continuing from fertilization, the zygote undergoes a process called cleavage in which it asexually reproduces (remember that concept from the first section?) to create new cells called "blastomeres". They continue to divide. At eight cells they form a structure called a "morula", which becomes a hollow call called a "blastula". The blastula further develops to become a "blastocyst". The blastocyst develops into an "embryo" and "placenta". The placenta is the organ which connects the embryo to the uterine wall. The embryo uses the nutrients obtained from the uterus to continue development and becomes called a fetus around nine weeks post-fertilization. Approximately nine months later that fetus is born and is known as an infant.
Wait, but that would mean that a fetus is alive...?
Well yeah. Any discussion of that fact beyond acknowledging it will cause a train wreck of a derail though. Let's just accept it and move on.
No. That's fucktarded. My women's studies professor said it's not alive until it's born!
MOVING ON...
Further reading
Hopefully you've found this informative despite its basic nature. It really is a fascinating subject. If you would like to learn more about it and get all the details then I highly recommend the links below.
Medical Embryology - Difficult Concepts of Early Development Explained Simply
Embryology
Evolution of Sex
Evolution of sex data
Scientists peek at the early evolution of sex chromosomes
