From Genesis, God created Adam and Eve. How come we have so many races on earth if we came from the same parent? Is it because people changed physically by adapting to various climates? Or races were made when different languages were introduced in Genesis 11 vs 6-8? How can I explain the human race diversity given the literal Biblical account?
Based on the wording of your question, I assume you want a literalist/young earth creationist perspective. This isn't the only perspective in Christianity. Plenty believe in evolution, or one form of Old Earth Creationism or another. The last portion of this answer, on particular, will likely be jumped on by the OEC and Evolutionist crowds, as it's specifically a literalist/young earth creationist view.
Technically, from many Creationists point of view (Kent Hovind, Ken Ham, Henry Morris, me) there is only one "race" . The "human" race. The idea of dividing up God's people into an artificial grouping based on superficial differences is wrong, anti-Biblical, and offensive in and of itself.
The thinking described above is known as "scientific racism", and is generally denounced today, for good reason.
An interesting observation, taken from http://www.bible-truth.org/race.htm
The concept of "race" isn't Biblical, either.
The differences in skin color, hair color, curliness/straightness of the hair, and other traits that we, in our society call "different races" are minor variations. They can easily be attributed to simple genetic complexity -the same mechanism that causes my children to not look exactly like me, but similar to me, multiplied over many generations. As families became more spread out over the globe after the flood, the differences became more pronounced within the groups.
People have many genetic attributes. Of course genes are passed on to your children.
It's a well-understood biological phenomenon that small populations can lose material from the gene pool. For example: Suppose we have a genetic trait that has possibilities, called "alleles", big-A and small-a. We have two people who each have both alleles, that is, they both have Aa. Each passes one of the two on to their children. Which the child gets is basically a toss-up. Say that just by the luck of the draw they both pass the big-A to all their children. Then the small-a is lost. If no one from outside joins the community, the small-a is lost forever. Or if they manage to pass both A and a to their children, but more A than a, than in the next generation there may have yet fewer a's, and in the next fewer still, until it dies out. This can happen just by chance, or if there is something in the environment that favors A. Like if a gene makes you allergic to oranges and oranges are the main source of vitamin C in this particular place, then that gene will tend to die out. This is called natural selection. (And by the way, while natural selection is often associated with evolution, it was actually first described in a scientific paper by a creationist, Edward Blyth.)
After the Flood, Noah and his family must have had the genetic material for all the races that exist today. Perhaps, for example, Japheth was white and Ham was black and Shem was yellow, or perhaps they had the genes for all the races more mixed together between them. Either way, after the Tower of Babel people started to spread out across the world in different directions. The population at that time was still small, and little subgroups that went out would have been smaller still.
So, for example, the people who went to Africa either happenned to all have the genes to be black and so all their descendants were black, or the people among them with white, yellow, and red genes all died out and only the blacks survived to pass on their genes. It's commonly argued that black skin is better for survival in hot jungle environments and white skin is better for colder environments, so the white gene survived in Europe and the black gene in Africa. I used to think that was established fact, but lately I've heard it argued that it's just an assumption based on the fact that people in Africa are mostly black, etc. I don't know enough about the biology of it to have an informed opinion. Either way, whether non-blacks died out because of environmental factors or pure chance or were never there to begin with, Africa ended up black and Europe white.
So as people spread out and sub-populations separated, some genetic diversity in the various communities was lost. Blacks separated from whites separated from asians.
Note that genetically, the difference between races is pretty minor. I read somewhere that race is controlled by just 4 genes. (Sorry, can't give a reference on that, can't swear that it's true.) In India it's not uncommon for families to have a broad range of skin colors, and it's becoming increasingly common in the US as marriage between people of different colors becomes more common. There's no need to theorize that the genes for different skin colors somehow came along later, whether by mutation or some miracle. It would not have been at all difficult for 8 people to have all 8 alleles. Two people could have all the genetic material for all races, as long as they don't have any common alleles between them. (i.e. Adam could have been coal black and Eve lily white or vice versa, or each could have been a middling brown, or some other combination.)
The historical answer to this question has been that Noah's three sons - Shem, Ham, and Japeth - represent the three major races - the Whites, the Blacks, and the Asians. Here, for example, is a reference showing this understanding. Hal Lindsay's Late Great Planet Earth also made reference to this common myth that Noah's son's were the progenitors of the races. The Table of Nations is Genesis 10 is considered a "map" of the various races, and is used to pin the various movements of Noah's children.
(If you haven't figured this out by now, I most definately do NOT believe any of this. I'm just trying to reflect what would have been considered a fairly normal 18th / 19th Century understanding of where the idea of race came from. I feel obliged to say "Thank You, God for changing our understanding!!)
According to the YEC perspective, races were created (or at least furthered; see AffableGeek's excellent answer) at the Tower of Babel. In Genesis 11:6 it states "The Lord said, 'Behold, they are one people, and they all have the same language...'" Then in verse 7 and 8, it states "'Come, let Us go down and there confuse their language, so that they will not understand one another’s speech.' So the Lord scattered them abroad from there over the face of the whole earth; and they stopped building the city."
This scattering thus resulted in different races.