Human descent is a difficult research area with various theories as to its nature. The Bible seemingly teaches common ancestry of the entire human species. We will see if and to what extent this can be in line with current scientific research and theory.

The Birth of and Propagation of Homo Sapiens

We are told in the Bible that while Adam had Seth born to him when he was 130 years of age, he also had “other sons and daughters” (Gen5:4).

(footnote- A Christian geneticist Joshua Swamidass has written his version of this in The Genealogical Adam and Eve: The Surprising Science of Universal Ancestry, 2019. Only having heard interviews related to it, it just seems too complicated for me to wrap my head around, though I haven’t made a massive attempt, I have to say. In it Dr. Swamidass seemingly postulates that although Adam and Eve were the couple from which all modern day humans are descended and indeed a mere 5000 years ago, yet there were other human generations before them, merely that they did not pass down their genes and that their bloodlines died out).

Monogenic Descent

In my view, genetics would have worked to bring forth the first man and first woman. This should be true of every new species- the mating pairs of the members of new species do not all spring up simultaneously, indeed it is even possible that an entire new species be populated from only a single mating pair. After all, workable mutations are extremely rare, the vast majority of mutations are deleterious to the health of the progeny. We see this in human biology all the time, babies are still-born when they incur mutations that are not compatible with life, this is why approximately 1 in 8 pregnancies ends in a still-birth (rather than result in super-powers!) The fact that we have never seen new speciation in humans in living memory, rather only archaeologically, tells us something of how rare they might be.

What this means is that if homo sapiens is to transform into some new futuristic species, it is likely to result from a single incidence of a mutation that manages to get passed on. Plenty of these “one-offs speciation” likely die off because they did not meet a similarly mutated partner, (or were not found attractive by them).

Once there is a mating pair, though, they hypothetically quietly re-populate the rest of the world through their superior adaptability. This seems like an odd hypothesis because we do not ever seem to see anyone that we might point at and say “that’s a new superior species!” All that has seemingly changed since ancient times seems to have been a possible gradual average increase in height. We might by faith hold that the first two homo sapiens did meet and did pass their genes on, these were Adam and Eve, and in this manner, there was none before them.

Polygenic Descent runs into Problems with Traditional Original Sin Doctrine

The doctrine of Original Sin is held to by most of the traditional churches in Christianity, and this doctrine does not allow room for the possibility of polygenic descent. The problem is that being not of Adam’s lineage themselves, they would not inherit Original sin from him.

In this regard, the Roman Catholic Pope Pius XII stated:

“When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains either that after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parents of all, or that Adam represents a certain number of first parents. Now, it is in no way apparent how such an opinion can be reconciled that which the sources of revealed truth and the documents of the teaching authority of the Church proposed with regard to original sin which proceeds from a sin actually committed by an individual Adam in which through generation is passed onto all and is in everyone as his own” (Humani Generis 37).

The Catechism of the Catholic Church states:

“The story of the creation and fall of man is a true one, even if not written entirely according to modern literary techniques. The Catechism states, “The account of the fall in Genesis 3 uses figurative language, but affirms a primeval event, a deed that took place at the beginning of the history of man. Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents” (CCC 390).

The Soul of Homo Sapiens

Only Adam and Eve are given a soul, because of all the homo, only he/she could appreciate the existence of a Creator. That is the main essence of the new species homo sapiens, “made in the image and likeness of God”. Can this be proven archeologically? It is unlikely that we will never knew whether other homo species knew God or not. The most I have seen in the literature is evidence that some may have buried their dead and even had burial rituals, though this too is not definite. Although this might sound impressive at first, it also true that an animal like an elephant tends to its dead too, as well as some other members of the animal family.

The Kane Question

We really have a fixed number of possibilities when it comes to the issue of the progeny of Adam and Eve and harmonizing it with the issue of Kane going out into a world that is inhabited at least to some extent.

Accommodating for Single Descent

There were other peoples when Kane was banished into the world. In order to adhere to strictly monogenic descent of all human beings which we proposed in the previous section, these peoples would have to be either the product of marital relationships between Adam’s own offspring, else they would have to be other homo species.

We consider the first of these two possibilities here. The problem with single descent is really the timeline. For a “people” were to arise from Adam and Even would take a minimum of between of 45 and 50 years, at the least up to the generation of the adulthood of their great-grandchildren, according to rough calculations I performed in the next section.

Seth seems to have been the third son of Adam, born to him when he was 130 years of age (Gen.5:3). Genesis 4:25 seems very clear that he is born after Cain and Abel. It would then seem that any people that arose would have to do so from the loins of Abel alone from relations with daughters of Adam. It would seem unreasonable to posit that they were from Kane, given that he gives no indication of kinship with them (rather seeming to fear them greatly). The alternative is that the “other sons and daughters” born to Adam, which is mentioned following the birth of Seth (Gen.5:4) might actually be interspersed in reality prior to Seth’s birth, since their times of birth are not explicitly mentioned.

This is why the “other species” hypothesis (below) seems to hold more ground, and is also able to give a more complete picture of the evolution of genus homo.

Trying to do some numbers…

Were every girl child born of Eve’s line to give birth aged 15, it would take the great-grandchildren 45 years to grow to adulthood, or 50 years were they to do it aged 17 (and only 35 years aged 12). This is taking into the account the fact that Eve herself is already of child-bearing age.

I would estimate that for a sizeable and self-sustaining population of Adam and Eve’s inbred descendants to come into existence would take at the very least four generations (the great-grandchildren grown to adulthood). This is my rough calculation of the numbers:

I come from a large family on my mom’ side and the number of cousins in all runs into around 40. Were my grandma to live to 100, she might have seen a 120 of her great-grandchildren grown to adulthood. However our reproductive rates all declined with each generation. Had the “rate of 8” continued, that number would have been 64 and 500 in the 2nd and 3rd generations respectively.

And if Eve had continued to be reproductive for centuries as with her children, then then one would probably add half that number over again, so that the number is 750. Of course, in the case of my grandma, the children required to take wives outside the family tree, which doubles the number of parenting couples. So perhaps we need to halve that number again.

What we’re relying on here at every step to sustain this early exponential growth is the veritably super-human fertility and strength of the women of old starting with Eve, and the vastly increased lengths of their reproductive spans prior to menopause.

Descent of the other Peoples from other Homo Species

An alternative explanation is that the other peoples really are the the previous homo species. This would seem to be the most workable hypothesis. If any of these did survive into the Flood, they are all wiped out in it anyway- I am agnostic with regards to the literalist view of the “Global Flood” account. the option seems much more feasible. The surrounding peoples were non-human species. This would mean that were humans to mate with them, likely the offspring would be still-born. While it is true that one of the criteria for differentiating species is that members of different species would not be able to mate, I’ve seen some references in articles to the possibility that homo sapiens did and could mate with other homo species. I do not know any way to verity of possibility nor the veracity of this. This only solves the problem of the other people whom Kane comes across, it still requires that the human population was initially inbred. When you go down sufficient generations, inbreeding ceases to be relevant. We are certainly not told of any sibling mating couples in the Bible, so this is reading into the text.

Kane’s wife and lineage

Were Kane to marry from Adam’s lineage, he would need to meet his spouse in his exile, which is not impossible. It would not seem acceptable that he married into non-homo species, since the names of his progeny are mentioned in the Bible for a few generarions (Gen. 4:17-22), and we would assume they were all homo sapiens.

Other Articles

this is a copy of a good article from bible.org:
“While some understand the reference to Adam in Genesis to be a general reference to mankind as a whole or the creation of more than one couple, most conservative scholars reject such a view and understand the Genesis account to refer to the creation of a literal Adam and Eve as a single couple. This is further supported by the NT. For instance Paul understood the OT to refer to a literal Adam and Eve (see Rom. 5:14; 2 Cor. 11:3; 1 Tim. 2:12-13). He clearly understood the reference to Adam and Eve to the first man and woman.

As to incest, it was not considered a sin and was not prohibited for Adam and early man. If the race was to populate and fulfill the command of Gen. 1:28, there is little doubt that Adam’s sons and daughters had to have married their own sisters and brothers if the race was to populate the earth, but due to the purity of the race as evidenced also by the long length of life, there were no adverse effects as we see happening today. Gradually, as the effects of sin took its toll on the human race, marrying one’s own sister, etc., began to create hereditary problems.

Here is Ryrie’s comment on this issue from his book Basic Theology (1986 ed) which I would highly recommend.

Though by many inerrantists the question of where Cain got his wife would not be considered a problem at all, this question is often used by those who try to demonstrate that the Bible is unreliable in what it claims. How could it claim that Adam and Eve were the first human beings who had two sons, one of whom murdered the other, and yet who produced a large race of people? Clearly, the Bible does teach that Adam and Eve were the first created human beings. The Lord affirmed this in Matthew 19:3-9. The genealogy of Christ is traced back to Adam (Luke 3:38). Jude 14 identifies Enoch as the seventh from Adam. This could hardly mean the seventh from “mankind,” an interpretation that would be necessary if Adam were not an individual as some claim. Clearly, Cain murdered Abel and yet many people were born. Where did Cain get his wife?

We know that Adam and Eve had other sons and daughters in addition to Abel, Cain, and Seth (Gen. 5:4), and if there was only one original family, then the first marriages had to be between brothers and sisters. Such marriages in the beginning were not harmful. Incest is dangerous because inherited mutant genes that produce deformed, sickly, or moronic children are more likely to find expression in children if those genes are carried by both parents. Certainly, Adam and Eve, coming from the creative hand of God, had no such mutant genes. Therefore, marriages between brothers and sisters, or nieces and nephews in the first and second generations following Adam and Eve would not have been dangerous.

Many, many generations later, by the time of Moses, incest was then prohibited in the Mosaic laws undoubtedly for two reasons: first, such mutations that caused deformity had accumulated to the point where such unions were genetically dangerous, and second, it was forbidden because of the licentious practices of the Egyptians and Canaanites and as a general protection against such in society. It should also be noted that in addition to the Bible most other legal codes refuse to sanction marriages of close relatives.

But here is another issue to consider. If one accepts the evolutionary hypothesis as to the origin of the human race, has that really relieved the issue of incest? Not unless you also propound the idea of the evolution of many pairs of beings, pre-human or whatever, at the same time. No matter what theory of the origin of the human race one may take, are we not driven to the conclusion that in the early history of the race, there was the need for intermarriage of the children of the same pair?”

the full article here: https://www.catholic.com/tract/adam-eve-and-evolution