How closely related are people to each other? And how closely does our genome match up with those of other primates?
Mark Napier, Frederick, Maryland
Jonathan Marks, a biological anthropologist at the University of North Carolina at Charlotte, replies:
Biologists estimate that any two people on Earth share 999 out of every 1,000 DNA bases, the “letters” of the genetic code. Within the human population, all genetic variations—the inheritable differences in our physical appearance, health, and personality—add up to just 0.1 percent of about 3 billion bases. This uniformity implies humans descended from a relatively small group of ancestors. Chimpanzees and gorillas (humans’ closest primate relatives) are roughly 5 to 10 times as genetically diverse, even though they have much sparser and more localized populations.
Overall, the genetic gap between a human and a chimpanzee or a gorilla is estimated to be about 20 times as great as the gap between any two people. That is still not a huge disparity: When we write out the DNA sequences of a human and a chimpanzee and place them side by side, we find that 98 to 99 percent of their bases match perfectly.