We tend not to see beyond the facial features that we use to identify "race," which is why we often think that the individuals belonging to a different group all look similar.
[Mapping human history, Steve Olson, p43]

Most human groups are the products of culture, not biology. "Racial" and ethnic groups are also products of culture.
[Mapping human history, Steve Olson, p49]

All humans everywhere in the world have exactly the same set of genes. But many of the genes come in slightly different versions. These differences in the DNA sequences of our genes lie at the base of our physical uniqueness.
[ Mapping human history, Steve Olson, p17 ]

Cells are the fundamental working units of every living system. Each cell has 46 human chromosomes, 2 meters of DNA, 3 billions DNA subunits (A, T, C, G), Approximately 30,000 gene code for proteins that perform most life functions.
[ U.S. Human Genome Program ] [ Image Credit: P164, DNA | The Secret of Life, James D. Watson ]

Except for the X and Y, the two members of each chromosomes pair are almost identical. Each chromosome contains a single strand of deoxyribonucleic acid, or DNA.
[ Mapping human history, Steve Olson, p15, p16] [ Image Credit: P11, DNA | The Secret of Life, James D. Watson ]

DNA carries the genetic information in the cell and is capable of self-replication. Each DNA molecule contains many genes — the basic physical and functional units of heredity.
[ Human Genome Project ] [ Image Credit: Cover, DNA | The Secret of Life, James D. Watson ]