@rocklee fun fact: Humanity actually has an age. It's very young. With simple mathematics, if we are assuming all human beings initially have identical mitochondrial DNA, then the human race is 300 generations old. Generations are often considered to be 20 or 25 years long, so if it's 20 then humanity is 6000 years old. If it's 25 then humanity is 7500 years old. But that's just one of the theories. The second one is an assumption that the human race is 40000 years old. However, chromosomes mutate much faster in males than in females. This means that the Y chromosome will mutate twice as fast as the X chromosome. So, it changes the age from 40,000 to 20,000.