What makes a person more hairy than another person? Where does hair usually grow during puberty? How come some men don't have chest or stomach hair at all? Is it because they shave it? Does stomach hair grow in a line or just in random places?
Body hair is a genetic trait just as skin tone, hair color, and eye color is determined by the combination of genes that you receive from your parents. Actually, if you simply measured the number of hair follicles on your body, you will find that you have great number of them, but almost all of them are vellus hairs, these are short, fine, unpigmented hairs that covers most of a person's skin. The hairs we normally take note of are called terminal hairs. These are the hairs that are longer, thicker, and have some sort of pigmentation.
Some hair follicles respond to androgens, the male hormones, and turn from vellus hairs into terminal hairs. From childhood we have terminal hairs on the top of our heads and as eyebrows. When puberty comes and the male hormones rise, other areas of the body begin to respond and change. Pubic hair and underarm hair usually form first. It is then followed by leg hair and arm hair. These are the most common hairs found across the world in adults. Facial hair, chest hair, and back hair is more variable between men.
Yes, some men shave their body hair as fashion might dictate. For example, the ancient Egyptians saw body hair as a sign of uncleanness (some suggested that it was because of lice) and totally shaved their bodies. This is why Joseph shaved before coming before Pharaoh (Genesis 41:14). God even required total body shaves when a person was cured of leprosy (Leviticus 14:8-9). But people generally do it today to make themselves look younger than they actually are. That is because the amount of body hair you have continues to increase even after you reach adulthood. It doesn't peak until you are in your thirties. Even in old age you will find hairs growing where you don't want them -- on your ear lobes, on the end of your nose, or on your forehead -- even while you are losing hair from the top of your head.
There is a strip of hair that is very common to men which grows from the pubic area up to the belly button, and some times beyond. It generally appears during stage 4 of development. Most body hair fills different regions of the body, but not necessarily in a line.