What causes the change in DNA for evolution to occur?

"Evolution and genetics are the primary factors which have caused some 90% of the earth's population to not have enough room in their mouth to allow the wisdom teeth or third molars to come in as normal healthy teeth.





Evolution over millions of years has been one theoretical cause. As the human diet has changed, we have in general developed smaller jaws."


http://www.mrllc.net/procedures/wisdom_t...





Is something directly causing genes to change or something else- I always thought evolution occurred solely by mutations.





Sorry if this isn't clear I'm not really sure how to phrase the question

What causes the change in DNA for evolution to occur?
Compared to our ancestors, modern humans have evolved slightly smaller skulls yet slightly larger brains. In the process, our face has flattened, and our jaws have shortened and moved lower and further back on our skulls. There are several interconnected reasons for these anatomical changes - all of them are the result of selective traits that contributed to our species’ survival (at the cost of impacted and infected wisdom teeth).





The wisdom teeth helped our evolutionary ancestors chew and digest a rougher diet - big strong teeth had a selective advantage - but as pre-humans moved to new environments and learned to use fire, their diet changed and big teeth were no longer an advantage.





What gradually became more important than big teeth in pre-human society was communication. The ability to rapidly convey complex ideas allowed them to hunt in groups, better defend themselves, and, perhaps even more significantly, pre-humans that were genetically predisposed for better communication, reproduced more. Speech undoubtedly contributed to survival and favored a larger brain for processing language as well as a reduced human jaw that allowed distinct vowel and consonant sounds. The rise of speech and the flattening of the face also caused a reduced nasal cavity and a decline in the human sense of smell - this also encouraged a larger brain that allowed observation and higher reasoning to make up for less olfactory input. In addition, the use of tools and the evolution of more dexterity in the fingers also contributed to larger brains.





What drove these changes was evolution – the favored reproduction of individuals with more suitable traits for the environment at hand. The way this proceeds is through variation in human traits - genetic differences in brain size, tooth size, etc. These genetic differences occur during random recombination and crossing-over at inception. When our genes are shuffled in this way it produces a huge array of genetic possibilities or variation. When a new variation of a gene is produced (say genes that encourage smaller rather than larger teeth), it’s called a mutation - mutation in the evolutionary sense refers to a novel genetic difference, it does not mean a monster or some sort of disfigurement. If the genetic mutation becomes fixed in a population (because it’s advantageous) it becomes part of that population’s normal variability and is no longer considered a mutation (people with smaller teeth, or different colored eyes, or taller individuals are not considered mutants although these traits are often the result of genetic mutation). In the case of wisdom teeth, certain random individuals were born with wisdom teeth genes that never turned on; the genes were still there but they were never expressed. These people survived better than others because they never experienced wisdom tooth decay and infection (which untreated will often lead to necrotic bacterial infection and death). That’s why some modern humans never grow wisdom teeth – the gene has spread that much in our population. Of course modern dentistry has now removed the selective advantage of the genes that suppress wisdom tooth eruption so the spread of these genes is slowed.
Reply:Mutation and genetic drift are the mainstays. Genetic drift is why you don't look like your sibling.





But, we keep looking for and hope to find a sort of pseudo-Lamarckian mechanism. Some way for environmental changes to back feed into the next generation in some directed, useful fashion. So far, I haven't seen any convincing example, but it would be handy and would give evolution just enough of an extra push in the right direction to explain it's apparent speed at times.





Although it has been anathema in the past, some feedbacks can be imagined. There maybe mechanisms that weed out some, randomly formed sperm in the same sort of fashion that the immune system is 'informed' by what we are exposed to.





It could be as simple a thing as a sort of 'mutate more' command. Some way for information you weren't born with to feed back into your progenetor cells in some useful manner.
Reply:Yes, you are right. Mutations lead to evolution. Prehistoric human with mutations for smaller jaws are able to survive better than those with larger ones because they are able to chew better. Maybe their food required less tearing and chewing with the advent of fire and cooked food. So, those that have smaller jaws will be more likely to pass on the feature to future generations and eventually the whole population aquired small jaws. And so we are here, small jaws and all!
Reply:It is survival of the fittest. If a creature's environment is constant it tends to reject genetic mutants. If the environment changes genetic mutants that are more adaptable to the new environment will be the ones chosen for mates. On a very large scale we see that many mammals that live in the oceans once had four legs that mutated into flippers so the mammals could live in water for what ever need that met. We find that polar bears and grizzlies are the same creature with different colors to accommodate their environment, etc.