New Defender's Study Bible Notes
6:1 multiply. God had commanded Adam and Eve to “multiply” (Genesis 1:28). With each man and woman enjoying hundreds of years of parental productivity plus almost ideal environmental and climatological conditions, the earth could well have been “filled” with people long before the Flood. For example, an initial population of two people, increasing at the rate of 2% annually (estimated to be the annual growth rate at present) would generate a population of well over ten trillion people in 1656 years (the time span from Adam to the flood).