2011-05-24, 01:41 AM
Sun tanning is actually a really good example to use for this.
When you tan, your body is actually going through a cause-and-effect cycle. The increased exposure to UV light causes the pigment cells (melanocytes) in your skin to produce more melanin, the pigment that causes your skin to be darker. Without being tan, the amount of melanin your skin produces is genetic. DNA codes for, ultimately, proteins. These proteins shape your phenotype. More then one gene is responsible for skin color in humans and the combination of all these genes working together produces your skin color. A population evolves to become more tan in a high UV exposure environment when individuals who are genetically more tan end up surviving more then individuals who have genetically lighter skin, and having darker skin becomes more prevalent in the population. The darker individuals have more success because melanin blocks UV light from damaging DNA, so having that natural advantage is the key in this hypothetical scenario. The UV damaging the DNA and causing mutations isn't the source of variation and evolution (solely); the most successful individuals surviving and reproducing is.
The environment is what drives natural selection. Those individuals that can survive in the environment reproduce; those that cannot survive in their environment do not get that chance. New traits that arise from mutations are also subject to natural selection. If that trait is beneficial, it may become a dominant trait in a population. If it's not beneficial, it will probably die out. I hope I explained that ok.
When you tan, your body is actually going through a cause-and-effect cycle. The increased exposure to UV light causes the pigment cells (melanocytes) in your skin to produce more melanin, the pigment that causes your skin to be darker. Without being tan, the amount of melanin your skin produces is genetic. DNA codes for, ultimately, proteins. These proteins shape your phenotype. More then one gene is responsible for skin color in humans and the combination of all these genes working together produces your skin color. A population evolves to become more tan in a high UV exposure environment when individuals who are genetically more tan end up surviving more then individuals who have genetically lighter skin, and having darker skin becomes more prevalent in the population. The darker individuals have more success because melanin blocks UV light from damaging DNA, so having that natural advantage is the key in this hypothetical scenario. The UV damaging the DNA and causing mutations isn't the source of variation and evolution (solely); the most successful individuals surviving and reproducing is.
The environment is what drives natural selection. Those individuals that can survive in the environment reproduce; those that cannot survive in their environment do not get that chance. New traits that arise from mutations are also subject to natural selection. If that trait is beneficial, it may become a dominant trait in a population. If it's not beneficial, it will probably die out. I hope I explained that ok.