According to the Bible, God created no other people besides Adam and Eve. Adam was created from the dust of the earth, while Eve was created from Adam (perhaps his rib).
Genesis 5 indicates that Adam and Eve had quite a few children. We have names for Cain, Abel, Seth, other sons (plural) and daughters (plural). So, at a minimum, they had seven children. If we assume that the birthrate for women is just equal to that of men, then Eve may well have had five daughters, pushing the total to ten. The earth at that time was very fruitful, and people lived a very long time, so she may well have had more than that.
Genetically speaking, it is not impossible at all that one couple could give birth to all humanity. Just because one scientist asserts something to be true does not make it so.
See this article regarding skin tones and this article regarding a challenge to that claim altogether.