Number of Possible Humans

Assuming single nucleotide polymorphisms* account for all genetic variation**, the number of possible humans is roughly equal to 2 to the power of the number of single nucleotide polymorphisms in the human genome. This is 2 to the power of 10,000,000 to 30,000,000 which is 10 to the power of 3,010,000 to 9,030,000. (For comparison, the number of atoms in the universe is about 10 to the power of 80.) This also assumes that people with the same genes e.g. twins, are the same person.

* where there is only a one molecule difference between people at a particular spot on the genome

** Single nucleotide polymorphisms actually account for about 90% of human genetic variation.