Why do black people have nappy hair?

People predominately from Western Africa (not the entire continent of people have extra kinky hair - Eastern Africans like Ethiopians for example) have extra kinky hair as a defense mechanism against the sun. Same reason our skin is so dark.

Darker skin has more melanin (sp. sorry) and more concentrated this is, the more protection you have against the sun. That's not to say you are immune, but if you are living in an extremely hot climate like West Africa, and you're living before sunscreen was invented, you have way more of an advantage if your skin contains high levels of melanin.

Hair on the top of the head that coils and coils and is very dense and close to the scalp protects your scalp/head from the sun as well. So when you're out gathering food and water all day and/or hunting, the sun won't fry your brain. So the original man, because of where he was located, evolved to have extremely dark skin and extremely coily/kinky hair to protect him from the sun's exposure.

Thousands of years ago, as people started to migrate and populate the world, they evolved or changed, just like any other animal, to adapt to their environment. Those who moved to much colder climates needed more vitamin D in their skin and did not require or need so much melanin so they paled. Their hair got less kinky so it could help warm them as it was easier for the hair to show length the straighter it is.

If you look at the planet, you can pretty much see that people look the way they look in response to their environment. It's not perfect (because of other nations conquering other nations, producing different looking people than the original people that were there) because the adaption takes thousands of years, but that's why people look different in a nutshell. Once you know this it really makes racism look even more ridiculous.

Why are veins blue?

When someone asks the question "why are veins blue?" a likely response is that they're blue because the blood in veins is deoxygenated. While it's true that venous blood vessels carry a lower concentration of oxygen than their arterial counterparts, this isn't the reason for their blue appearance in your skin. Still, when someone invariably responds to the veins-are-blue-because-they're-deoxygenated argument with the observation that "I've never seen blue blood before" one might then hear the slightly more sophisticated-sounding but increasingly far-fetched claim that we don't ever observe blue blood because it is immediately oxidized upon contact with air.

Wrong. Blood is never blue. Ever. Period. (And, this is an excellent example of why you should never ingest information from Yahoo Answers uncritically.)

The bright red color of arterial blood stems from a complex that's formed between hemoglobin, iron, and molecular oxygen. This complex mainly absorbs higher energy (shorter wavelength) blue and green light, leaving behind primarily just red wavelengths for our eyes to detect. However, even when blood is largely depleted of oxygen, it is never blue: it's more of a deep maroon color. And, although I have not participated in a surgery myself, those who have (including my girlfriend, a veterinary student) assure me that in surgery, veins within the body do not appear blue either. So, not only is blood not blue, veins on their own aren't either. "Blue veins", then, are a phenomenon unique to the skin.

So, what's going on here?

The most comprehensive answer that I've been able to find comes from a paper by Kienle et al. published over twelve years ago in the journal Applied Optics and entitled "Why do veins appear blue? A new look at an old question". Based on the findings of the authors, three reasons emerge for the blue appearance of veins in skin. The first two are physical and stem directly from the way in which light interacts with blood (how it is absorbed) and with skin (in this case, how light is reflected). The final reason is psychological, dealing with the way in which our brain processes information relatively to generate color perception. (Greg Laden sort of hinted at some of this recently on his blog).

Since the paper in question is a study in optics, it is way outside of my area of expertise. So, just in case you wanted an in depth technical critique of its methodology, you're not going to find it here. However, I can give you a basic summary of the paper's major findings. And then, if you still have the desire (and the ability) to explore the subject in greater depth, you can parse through the paper yourself.

To tackle this problem, the authors measured how much light of various wavelengths was reflected from both real blood vessels in skin and imitation vessels in a skin-like environment, using a sophisticated technique that gave them spatially-resolved measurements. The synthetic vessel (which was a capillary tube filled with blood and placed in a milky substance with optical properties similar to skin) allowed the authors to experiment with a variety of parameters (particularly vessel depth and diameter), and they were then able to validate their results by taking measurements on actual vessels in skin. Using this set-up, they were able to demonstrate that the optical properties of skin and blood (combined with the influence of relative color perception) explain why veins in skin appear blue, despite not actually being blue.

Skin does not absorb much light at any wavelength, making it look white (depending on how much melanin is present, of course--making this discussion only really relevant to people with lighter skin). Blood, on the other hand, absorbs light of all wavelengths (but less in the red part of the spectrum). However, blue light does not penetrate the skin as well as red light. If a vessel is near the surface of the skin, almost all blue light is absorbed by the vessel, so even though only about 1/4 of the red light is reflected, the ratio of red light reflected to blue light reflected is about 10:1. This vessel appears red.

If the vessel is deeper (about 0.5 mm or more), not as much blue or red light will be absorbed. Importantly, this effect will be more pronounced on blue light than on red light since blue light doesn't penetrate skin very well (the ratio of red light reflected to blue light reflected is about 3:2 or less). This is the case for the "blue veins" observed in skin. Once the vessel is deep enough, though, it won't be seen at all, as light of all wavelengths will be reflected before it can interact with the blood.

Perplexingly, this 0.5-mm-deep vessel appears blue despite reflecting slightly more red light than blue light. This is where relative color perception comes into play. The surrounding skin reflects more red light than blue light (by a ratio of about 5:3), and it does not absorb as much of either type of light as a blood vessel does. Since vision is influenced in part by relative perception, if something purple is placed next to something red, the purple object will appear blue.

None of this, however, addresses the question of why veins specifically appear blue. To answer this one, I can fortunately once again rely on the expertise of Meredith, my vet student girlfriend. The reason why only veins appear blue is that veins are the only vessels we actually observe through the skin. This is due to the fact that veins are larger, have thinner walls, and are more superficial than arteries (and, no, I don't meant that veins prefer People or Us Weekly over The New Yorker--"superficial" is just medical speak for closer to the surface). All of these aspects of veins have clear biological rationales. Beyond just carrying blood back to the heart, the primary function of the venous system is as a blood reservoir. In fact, about two-thirds of your blood volume is held in your veins at any given time, hence their larger size. Because the heart has to push blood directly through arteries, their walls are subject to higher pressures than the walls of veins, so they need to be thicker. Finally, veins are located closer to the surface of the skin, because they also play an important role in heat exchange with the outside environment (to help cool the body). Arteries could perform this function just as well, but it's much more advantageous to keep those higher pressure blood conduits deeper in the body and protected from injury.

The take-home message here is that the bluish appearance of veins in the skin has everything to do with where they are located, and nothing to do with the concentration of oxygen within them. In fact, if we could see them through the skin as well, even arteries would look blue.

Why are men attracted to breasts?

Humans are from a family of animals called the Hominids. This includes other animals like the Chimpanzees. Second, Humans are the only Hominids where the breasts remain swollen at all times. All other Hominids have flat chests, except when lactating. Third, Humans are the only Hominids who walk upright at all times.

So, here's the answer. All other Hominids use the buttocks as their sexual attractor. But Humans walk upright and frequently are facing each other. So, Humans evolved permanently swollen breasts as an alternate sexual attractor. You will note that the general shape of the human breasts is similar to the buttocks: rounded with a cleavage between them.

Larger breasts more closely resemble the shape of the buttocks. This is the reason larger breasts tend to be more attractive, not because they "feed the babies better." Also, the breasts tend to swell a bit more when the woman is ovulating. So, larger breasts also suggest fertility.

Why are lips red?

First of all, did you know that the outline or the border of your lips (called the vermillion border) is a special feature of humans only? This transition line from your skin to the pinkish-red part of your lips is found only in humans—no one knows why.

The lips appear red because of the underlying blood vessels. Arteries are blood vessels that carry blood back to the heart. The arteries and veins are connected through a series of blood vessels called the capillaries.

These red-colored blood filled capillaries are close to the thin skin on your lips, so your lips appear red.

Why are all babies born with blue eyes?

You inherit your eye color from your parents, but no matter what the color is now, it may have been blue when you were born. Why? Melanin, the brown pigment molecule that colors your skin, hair, and eyes, hadn't been fully deposited in the irises of your eyes or darkened by exposure to ultraviolet light. The iris is the colored part of the eye that controls the amount of light that is allowed to enter. Some other animals are born with blue eyes, too, such as kittens.

Melanin is a protein. Like other proteins, the amount and type you get is coded in your genes. Irises containing a large amount of melanin appear black or brown. Less melanin produces green, gray, or light brown eyes. If your eyes contain very small amounts of melanin, they will appear blue or light gray. People with albinism have no melanin in their irises and their eyes may appear pink because the blood vessels in the back of their eyes reflect light.

Melanin production generally increases during the first year of a baby's life, leading to a deepening of eye color. The color is often stable by about 6 months of age. However, several factors can affect eye color, including use of certain medications and environmental factors. Some people experience changes in eye color over the course of their lives. People can have eyes of two colors. Even the genetics of eye color inheritance isn't as cut-and-dried as was once thought, as blue-eyed parents have been known (rarely) to have a brown-eyed child!