 In the first few years of a child's development, you see the fragile body of the baby quickly growing and becoming stronger. You see its height and weight start to increase rapidly. This makes sense because the initial priority of the body is to become strong enough so that it can survive. So all the energy is diverted to making you stronger and bigger. But then once you reach an age of about 10 to 12 years, that particular kind of development slows down. Now you don't see your height, for example, increasing as quickly as before. Why? Because now the priority changes. Now most of the resources and energies are used to mature the reproductive organs or the sexual organs. And this period of time, which is usually around teenage, where the sexual organs are maturing, we call that period the puberty. So let's explore the different changes that start happening in the body during the time of puberty. So let's start by writing down what puberty is. As mentioned, puberty is an age where the reproductive organs start to mature. So reproductive organs start to mature. Start to mature. And this usually happens around the teenage. For some people it could be a little bit earlier, like maybe around 11, 12 years. But for some people it can be a little bit later also, maybe for about 15 to 16 years. So it varies from individual to individual. And if you're wondering, what do we even mean by this statement? Well, basically it's during this time your body starts to produce sex hormones. Hormones like testosterone or progesterone, etc. We have talked a lot about this in great detail in our previous videos called endocrine system. But anyways, it starts producing sex hormones which can affect your behavior. That's what happens for teenagers at times. And these hormones also cause mature gametes to be produced. Let's write that. They cause mature gametes to be produced. Basically, sperm cells and ex-cells. Spombs are produced in the testes and ex-cells are produced in the ovaries. That starts happening during this time. And as a result of this, we start seeing some physical changes in our body. So there are physical changes that start happening. And these are visible during the same time. Now, why do they happen? Well, there are a couple of reasons for that. One is that it signals a potential mate that the body's starting to sexually mature itself, right? So it's a signal that the body has started the sexual maturity. And another reason for these changes that start happening in your body is basically to prepare to prepare for a baby. And here's what I mean by this statement. For sexual reproduction, we know that the sperms have to go and unite with the ex-cells. We call this fertilization. But in some cases, fertilization can happen externally, like in some fishes. Here, the female fishes would lay the eggs first. And then the male fishes would go and fertilize that egg. So fertilization happens outside of the female body, right? But in humans, the fertilization happens internally, meaning inside the female body. So for this, the males have to release the sperms into the female body. And to do that, a very intimate act is needed called the sexual intercourse, right? And for that sexual intercourse, some physical changes need to happen in the bodies. And also after fertilization, once the baby starts growing, we know in humans the baby stays in the mother's womb for about nine months. So the mother also needs to prepare her body to be able to take care of that baby. So basically, a body is trying to signal for a potential mate and prepare for reproduction. So now let's see what are these physical changes that happen. Let's talk about those physical changes, physical changes. Now some of these physical changes are common to both the males and the females. So let's start with them. Let's start with the common ones. What are the common changes? Well, one common change that you will find is you'll start growing hair in different parts of the body. During this time, usually around armpits, around armpits, genitals, you also start growing very thin hair on your hands and legs and face, etc. So basically, these will start growing hair, they grow hair. You also see that the genitals, the skin near the genitals will start to darken. So the skin of the genitals darken. So the skin darkens over here. And another thing that happens because of the hormones that get secreted over here is that a lot of oil might get secreted and the skin ends up getting oily sometimes. So you might have oily skin. And that could result in pimples and acne that we usually see in teenagers during this time. But of course, that's not a necessary thing. Some people are lucky to not have those pimples. I remember I had a lot of pimples. All right, now let's talk about the changes which are exclusively for males and females. So let's make two columns, males here, females here. Let's start with the males. What changes do we see only in the males? We see their voice starts to crack. Their voice kind of starts becoming a little deeper, so voice cracks. We see facial hair growing, like beard and moustache. I'll just write beard over here. And we also see the penis starts to become larger. So penis enlarges. And the penis will be capable now of erection. Again, this is important for sexual intercourse. Now what are the changes that happen only in females? The breast starts to enlarge. So breast enlarge. The skin at the center of the breast near the tip of the nipple, that's starts to darken. So the skin darkens at the tip of the breast, all right, at the tip over here. And another thing we see is they will start to menstruate, menstruate. And of course, if you're wondering why this happens, we'll talk about this in a little bit more detail when we talk about the female reproductive organs in the future videos. So that's about it. Let's quickly summarize. What did we learn? We learned in first 10 to 12 years, the human babies grow to become stronger and protect themselves, but then the priority changes and now their normal growth slows down and their reproductive organs start to mature. This time is what we call puberty that happens usually around the teenage years. And as a result of this, some physical changes start to happen in the body. Some changes are common, whereas some changes are exclusive for males and females. And why did they happen? Well, they happen, one reason for that would be to signal a potential mate that the body has started is sexual maturity. And another reason is to prepare for a baby and to prepare for the act of sexual intercourse.