Steph

In our world, it doesn't matter anymore. Vit. D deficiency is irrelevent in developped countries so darker people won't die of it (no natural selection). second, skin cancer when caught early is rather easy to cure, so if you are pale and live in an area at risk (like australia), you just go see the doctor and get checked often. of course, you would have the odd death, but that wouldn't be statistically significant. Of course, going to underdevelopped countries, you have a different dynamic, but we are talking about thousands of years of evolution, whereas the time gap between poor and rich countries is at most 100 years (and i think i'm exaggerating).

All that your friend said is true but we are talking about Normal Flora, bacteria that won't usually cause disease. I may have worded it badly but what I meant is that bacteria shouldn't usually be found in the blood. This doesn't mean that no bacteria can grow, just that if they do, you are in trouble. Also, blood is not always sterile: for example, you can get cut and bacteria like C.tetani enter your bloodstream. btw, I am also a microbiologist.

You have three kind of cells (cones) that detect light at a specific wavelength. So to have a color deficiency, you can have: -Missing cell types (VERY rare) -The peak wavelength that the cells are sensitve to are shifted, or you have decreased sensitivity. for some reason, insensitivity to blue light is also rare.

Hi... I'm new here, but I just want to add something. Blood is sterile. There has been reports of bacteria and other microorganisms in blood, but those are controversial at best. If you aren't sick you shouldn't have any bacteria in your bloodstream. this said, I also think that in nature, you can never say never so...