If there were only Adam, Eve, Cain and Abel in the beginning, how was the world populated?
There are two answers to your question. How was the world populated before the flood is answered in a command God gave to Adam and Eve. The second part to your question is how did Abel find a wife? That answer is available from a previous question. So we will focus on the first one.
Command to Have Children
Genesis 1:24-31 tells us that God created Adam and Eve on the sixth day. After He created them, He commanded them to have children and to populate the world.
And God blessed them; and God said to them, “Be fruitful and multiply, and fill the earth, and subdue it; and rule over the fish of the sea and over the birds of the sky, and over every living thing that moves on the earth.” (NASB) Genesis 1:28
Adam and Eve were faithful to the Lord’s command and started populating the world. Cain and Abel were the first male children recorded in the Bible (Gen. 4:1-2). Seth came along later (Gen. 4:25). It was common to record the birth of only the sons and not the daughters. It was also common not to record all of the sons.
The world’s population continues to increase. It is currently estimated to be over 6.0 billion. That is a great number of people but it is not a difficult number to reach. A conservative calculation reveals that the world’s population by the time of the flood would have easily exceeded 6 billion.
The calculation is a rough approximation since we do not know the birth rate exactly. The calculation requires several steps.
Step #1 – Determine the time from Adam and Eve to Noah’s Flood. The ancestral line of the early families is given in Genesis 5:1-32 and 11:10-32. From the genealogical listings we can determine that Noah was born 1,056 years after the creation of Adam and Eve. Noah’s sons were born 500 years later and the flood occurred 100 years after Noah’s sons were born (Gen. 7:11). That means the flood occurred 1,656 years after the creation of Adam and Eve.
Step #2 – Ignore the initial years of population growth. Next we are told in Genesis 4:16-24 that an initial population of males and females were living on the earth. Since Adam and Eve were the first parents these humans were their offspring. Abel and Cain were named in scripture because they were involved in the first murder and sacrifice (Gen. 4:1-15).
Scripture reveals that Seth was born to Adam and Eve when they were 130 years old. Genesis 5:6 states that his first son was Enosh. He was born when Seth was 235 years old.
It is clear from Genesis that many children were being born who are not documented in scripture. If the first child of Adam and Eve were born when they were 30 years old and additional children were being born every two years, the world would have 21 children on the earth when Adam and Eve were 60 years old. Their first child would be 30 years old, using these assumptions. Assuming that this child, child A, married a brother or sister, say child B or C, within 2-4 years and started having children, this couple would produce 21 children on their 60th birthday or when Adam and Eve were 120 years old. If we go back to either child B or C, which did not marry child A, and we assume that child married child D or E, then that child’s marriage would produce 21 children when Adam and Eve were 124 – 128 years old. If we keep the process going it is easy to have 100 hundred children, at least, by the time Adam and Eve are 130 years of age, when Seth is born. Scripture typically does not record the birth of females or of all of the males. After 130 years only 1,526 years remain until the flood for children to be born. The flood started 1,656 years after the creation. Now there is a population giving birth to children.
Step #3 – Determine a birth rate for each couple. We will assume that each couple is giving birth to two children and then stops. This is unrealistic but it will make the calculation simpler. Realistically, they probably gave birth to at least 3 or 4 and probably more.
Step #4 – Determine a mathematical equation for population growth. To determine the population growth we will assume that Enoch has offspring about every 10 years. We will assume that each offspring does not have their first offspring until they are 117 years old and then they have a child every 10 years for only 117 years.
The number 117 years is the average age of the patriarchs when they had their first child as given in Genesis 5:1-32 and 11:10-32. Most likely there were other children who were born earlier but not recorded. Yet, we will ignore this factor. For example, Seth is the only child mentioned in the generations before Adam and Eve (Genesis 5:1-5), but Cain and Abel were born earlier. However, there not mentioned.
Using these assumptions, Enoch would have had 11 children in 117 years. Now we assume that each of these children had their first child at age 117 years and produced children about every 10 years, and their children followed the same pattern.
So if we divide 1,526 years (the number of years from Enoch to the flood), by 117 years (the period of procreation) we obtain 13. Now the formula for computing the world’s population by the time of Noah’s flood is given by the summation of,
This summation represents the number of children born to each descendant over 13 periods of 117 years each for a total of 1,526 years, starting from the birth of Seth when Adam and Eve were 130 years of age. The summation can be computed using the following well-known formula,
where a = 11, n=13. The result is 38 trillion people.
Thirty-eight trillion people is more than 6 billion people. We started only with Seth and ignored all of the other families on the earth. We ignored the death rate but that will not affect the total since we assumed they staring giving birth at 117 years of age and stopped giving birth 117 years after the first child was born.
How was the world populated? The answer is by two people – Adam and Eve and their children.
Reference Links:Where did Cain's wife come from?
How many kids did Adam and Eve have?