Updated: Sep 6, 2020
When Adam had lived 130 years, he had a son in his own likeness, in his own image; and he named him Seth. After Seth was born, Adam lived 800 years and had other sons and daughters. Altogether, Adam lived a total of 930 years, and then he died.
It makes sense to me that Adam could live to be 930 years old. After all, he was fashioned directly by God. Same thing for Eve. Genesis doesn't say specifically, but it seems likely Eve was also around for centuries, giving birth to Seth and his many brothers and sisters.
(Another thing: Skeptics like to point out that Adam and Eve's children would have to marry their siblings—pretty creepy by modern moral standards. In fairness though, these early people would have had virtually flawless genetics, so inbreeding wouldn't have been a concern. I know it's a little weird to think about, but I'm just saying.)
Genesis tells us Seth went on to live a long life and have many descendants. Of course, Seth wasn't Adam's firstborn son. That was Cain, who infamously murdered his younger brother Abel and became an outcast. Genesis 4 tells a little about Cain's life as an outcast, including listing some of his prominent descendants. Between Adam and Eve, Cain, Seth, and all the named and unnamed descendants, it seems like the human population pretty much exploded back in those days!
In fact, let's see if we can estimate the world population when Adam, the First Man, died at the age of 930. If Adam and Eve gave birth to Cain when they were 30, and added another boy or girl to their family every 2 years (give or take) after that, then by the time they were 430 years old, they would have 200 children! (I know we counted Abel, who was actually murdered, but don't worry—it's just an estimate.) Let's say they stopped having children when they got to 200. (Eve: "Yeah, that's plenty!") That’s 100 new couples! (Sorry, still weird to me that in this scenario, siblings are becoming couples.)
Now what if we use 200 children as our estimate for what each of those 100 couples decided to produce? And then each of those children couple up and start producing 200 more children per couple over roughly the first 400 years of their married life? And so on. And let's also assume most everybody else (not Abel, of course) was still alive when Adam died.
So are you good with mathematics? What would be the approximate world population when Adam died?
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ANSWER: By the time Adam died, the world population would be more than 320,000 people!