Mitochondrial Eve is the maternal ancestor of all living humans. Mitochondria are the tiny organelles inside of human cells that contain their own genome. Each person's mitochondrial genome is inherited from his or her own mother making mitochondrial lineages maternal. The is one type of DNA within a humans body along with chromosomal DNA. Every human's mitochondrial DNA can then be traced back to one source so all humans would then be related. It is important to emphasize that there was not only one woman living at that time. This woman has been estimated to have lived 150,000 to 200,000 years ago. Many other women are believed to have lived during this time. It is not known why there is only one mitochondrial DNA strand of humans today.
With all humans being related genetically, why then do we have a diversity of looks ago people such as skin color, hair color, eye, color, face shape, etc? We would attribute human differences to evolution. Just like the evolution we can study in species, humans have adapted to different environments over time. The mutations that occur in DNA through reproduction affect the next generation of species. We have natural selection, genetic drifts, bottleneck effects, and the founder effect from geographic isolation that plays into these changes. Overtime, the traits humans carry have been mutations that have survived over time as well as adaptations to our new environments.