If we start with two humans and the population doubles every generation, we can use exponential growth to determine the number of years it takes to reach 8 billion people.

Assuming a generation is around 30 years, we can use the formula for exponential growth:

N = N0 x 2^(t/g)

where:

• N0 = Starting population (2)

• N = Final population (8 billion = 8,000,000,000)

• t = Time in years

• g = Generation time (30 years)

Plugging in the values, we get:

8,000,000,000 = 2 x 2^(t/30)

Simplifying, we get:

2^(t/30) = 4,000,000,000

Taking the log base 2 of both sides, we get:

t/30 = log2(4,000,000,000)

t = 30 x log2(4,000,000,000)

t ≈ 305 years

Therefore, it would take approximately 305 years for the population to reach 8 billion people, assuming a doubling every generation of 30 years.