So M2-1 would start producing in a non-human breeding population and after a number of generations displace most or all non-humans with heterozygous humans, and then, eventually, with entirely homozygous humans. If the above description is correct, we must begin with a single human, gradually increase the number of humans to a very small number, gradually increase that number to a larger number, and then eventually increase their number to displace the non-human population entirely.

The population must eventually become completely homozygous so that no possible non-humans are produced. Possibly only the homozygous are truly human since the heterozygous individuals may have non-human characteristics expressed if the non-human allele is dominant. If this were the case, this could provide a mechanism for removing the heterozygous primates and the non-mutated primates since they could not compete as well.

My question is, How can someone say there has always been at least several thousand humans if we must start with one individual human and gradually increase that number?

Whoever wishes to answer this, once you do so, I will have one or more questions for you, but relatively simple ones I think.

Thanks to whoever might help me with this.

  Welcome to the ASA and to the forum! As you have likely discovered, we're an organization with many diverse views and perhaps you'll get several here.

  You have raised a very important question on one of the hottest topics of the day.

  My primary response is to point out that evolution must be discussed in terms of populations and not of individuals. Secondly, speciation occurs gradually and not through a single individual.

  In other words, there is a sense in which, except for simpler organisms that reproduce asexually or other rare cases, there seldom is a "first of a species." That is, virtually every birth is of the same species as its parents. Speciation occurs over time as a population is isolated in some way (geographically or culturally) and separated from another part of the population. Or the entire population drifts genetically until it differs from its ancestral population. So evolutionarily speaking, one never has a first of a kind. No "first" zebra, no "first" giraffe, no "first" dog or cat, etc. Similarly, no "first" human.

  Perhaps it helps to think of a continuum of mutations and it is a composite set of many mutations that eventually leads to a recognition that the population now represents a new species. One would never recognize it in the snapshot of a mere thousand years.

In this perspective, it is easier to see that a population bottleneck would limit the diversity of mutations. Hence, quantifying the extent of diversity of mutations today can lead to an estimate of the degree to which the population might have shrunk in the past. Mathematically, the equations might lead to more than one solution--trading off time vs bottleneck. That is, the diversity could be explained by a bottleneck of 10,000 individuals say 500,000 years ago but also by a smaller bottleneck of 1,000 about 4 million years ago. (these are arbitrary numbers to make a point). But usually, as in the roots of a higher order mathematical equation, these alternative solutions can usually be shown to be unrealistic. Furthermore, population geneticists these days have a lot of different algorithms they can use and an increasing mountain of data, so the projections are getting more and more credible.

 But, in the end, no "first" human is a feasible solution in population genetics.

Does that help?

Randy

One can imagine that in some cases it might happen that a very few founder parents could give rise to a new species, in cases of founders to an oceanic island, for example. That would be a different mechanism, and again the changes giving rise to new species (think Galapagos finches) will not come suddenly from two individual parents having that new offspring, but rather due to the differential survival of the great grandchildren and great great great great great...etc grandchildren of those founder parents, with the selective pressures "molding" the direction of the changes over long periods of time. 

If you want to learn more about natural selection, you can do worse than actually reading (or listening to Librivox audio version) of On the Origin of Species by You know Who. It's actually a very understandable and quite remarkable book (that is an understatement). http://librivox.org/the-origin-of-species-by-charles-darwin/

Blessings, 

Craig Story

P.S. My response to you and Craig will be out soon re the "original human population size."

The story of Genesis obviously has elements both of allegory/poetry while at the same time speaking truth about God, and humanity and their relationships.   The fact that the human species (however it is defined) has an evolutionary origin should not negate the need of man for repentance, and obedience to God's law, which is "written on our hearts."  It also should not negate the truths about Christ's role in salvation. We are now free to better interpret the meaning of Genesis/original sin/the Fall, etc based on our better knowledge of nature, that should help us better interpret the scripture. Just like when observations led folks to realize the earth was not the center of the universe, that led to better theologies of heaven/hell and the like. (in other words, hell is not down there in the earth, very far from the "heavens." 

God Bless,

Craig

Would anyone be willing to critique the following? Comments would particularly be appreciated since it is very possible I have misunderstood some of the scientific information.

So what theology might we end up with concerning human origins given the new evolutionary evidence that has come to the fore? First of all, the new evidence is pretty clear that common descent is pretty much undeniable and that we never had a bottleneck of two individuals for a breeding population. This is quite compatible with a first human couple living in the midst of a population of several thousand or more non-human primates with whom they and their children could interbreed. Natural selection will eventually remove all non-humans from the population. Genesis does not mention this wider population which would soon become extinct for much the same reason it doesn’t mention dinosaurs. Since the Bible is concerned to give only a certain type of information, no one needed to know about them.

How would these non-humans differ from humans? Consider first how the Fall would affect their differences. A better theology than Schneider’s would have the human tendency to do evil inherited from our animal ancestors but suppressed and held dormant in the first couple until the Fall. Thus the first couple would not be perfectly good but rather completely morally neutral and innocent until a free choice could be made to obey or disobey God. With the first free choice of disobedience, that animal tendency to do evil was again activated in the human genome. The non-humans would lack spiritual characteristics found in humans. They could not relate to God as humans do. They would probably not possess the same intellectual abilities since this deficiency could provide a good means for gradually selecting them out and diminishing their population. They would not be significantly different from fallen humans since humans had returned to their prehuman, animalistic state with its natural tendency to selfish, sinful behavior. Nevertheless, humans would have a natural awareness of good and evil (via the Fall) not possessed by the non-human primates and humans would be responsible for acts the non-humans would not b responsible for. Humans would be capable of great moral acts of which the non-humans would not be capable.

Henri Blocher pointed out that Genesis 1 is a unique form of literature in the Bible. He called it prose-poetry. Thus it would be more appropriate to interpret it poetically. The strict symmetry of the the chapter suggests that it is not speaking of a chronology of events but a listing of categories of existence—of light (fire), air, water, and earth—and that which inhabits these realms. Thus we would have no problem with any chronology issues like the sun appearing on the fourth day.

But Genesis 2 is complimentary to chapter 1. Kenneth Kitchen has pointed out that the same kind of pattern we find in these chapters, a general history followed by a detailed description of a specific aspect of that history, is found in some Egyptian inscriptions. Thus each chapter is to be seen as a different aspect of the same type of literature and Genesis 1 is not the only chapter to be interpreted poetically. For poetic interpretation, there does need to be some correspondence between the poem and the meaning, it cannot be just anything one wants it to be. For example, for Eve to be taken from Adam as Genesis describes might mean simply that Eve was Adam’s daughter by a non-human primate (shades of Lillith), it cannot mean that they are completely unrelated. (I’ve suggested in the last blog that Adam and Eve would more likely have to be homozygous with the human gene in order for them to be truly human. If this is the case, Adam could mate with someone who is heterozygous with the human gene to produce Eve who would then have the homozygous gene.)

The Genesis myth is set in the milieu of the agrarian revolution. If, as seems very likely, humans did exist before the agricultural revolution, perhaps the myth is taken from an earlier oral account that was updated for agrarian societies. Since we have seen that it should be interpreted poetically anyway, the original story may involve a Fall in a hunter/gatherer paradise (there are such environments even today) with the curse involving a loss of resources and constant movement and migrations. This would be analogous to the curse of labor by the sweat of the brow. Actually, it wouldn’t be a hunter/gather paradise but gatherer only. Adam did not need to hunt since the paradisal setting supplied all of his needs and God commanded him not to kill animals. Other elements of the curse would remain the same: pain in child bearing, submission of woman to man, etc. The Tree of Life and the Tree of the Knowledge of Good and Evil could fit just as easily in a gatherer setting. Adam simply did not originally tend the garden. In any case, the essential story and message of the myth remains the same. God allowed it to change with time but not in any way that would alter the message. Neighboring Near Eastern cultures may have taken the oral tradition of the original gatherer society myth or the developed agrarian myth such as the Hebrews received or revised it and then the NE societies altered the story in ways that did remove and/or distort the meaning of much of the original message.

At the moment, so far as I can see, the only other change this new scientific information might imply for my theology involves my view of the Flood. I’ve found Hugh Ross’ arguments for a geographically local but populationally universal flood persuasive for many years. The new scientific information would now require that the Flood not be universal for the earth’s population. But Ross’ arguments can be seen to lead to a populationally local flood as well. He has noted that the word for earth often depicts only a limited expanse of land. If all the animals on this land are destroyed, likewise only all the people from this area of land are destroyed (Genesis 6:7). If the flood occurred on the Mesopotamian plain or perhaps a then dry Persian Gulf, it may be that God did not consider the more limited populations of hunter/gatherers outside of this area to be quite so wicked. When the source of this story says that God saw the wickedness of humanity and decided to destroy it, this writer/speaker was only concerned about those humans of which he or she was aware. Possibly an entire civilization was the focus of God’s judgment. Those living outside of the flooded area may have very soon moved into this area after the Flood and mixed with Noah’s descendants. The Flood may still have decreased the world’s population substantially to produce a bottleneck (not of eight people but of a few thousand). The bottleneck suggested by Y-chromosome analysis might have occurred at the Flood. The studies suggest a bottleneck much later than that of the mitochondrial studies. And of course, it might not have been a flood at all. If this portion of Genesis is to be considered part of the original poetic myth of Genesis 1 and 2, then the point of the story is that God destroyed a large number of people, however that was done.

  You raise many important issues to discuss. Let me focus here on one of your original issues that started this topic. You state that " In any case a single individual will always be responsible for getting a new gene going that will make the new organism substantially different than the others." But I think what Craig and Keith and I were trying to say is that while it is true that a mutation, or small set of mutations, can occur in one individual and eventually propagate to 100% of the population, such mutations in complex organisms seldom, if ever, define a species or subspecies of the type that might differentiate humans from non-humans. Of all the characteristics that biologists and paleontologists use to identify a "human", I don't think there is any single one where they would define a precise value above which is a human and below which is non-human. In other words, the transition from non-human to human is more than a single, or several, generation's worth of changes. It may be more helpful to think of a continuum in each characteristic trait.

 As a result, if one differentiates human from non-human in purely biological terms, then the notion of a "first human" or a "first couple" is hard to sustain in light of our observations and understanding. That leaves a spiritual definition, which is an interesting option and which raises its own set of questions.

Between Craig, Randy and Keith you've had good answers to your original questions, but I fill in a bit here and there.

One thing to note is that "new" mutations are not the only way to produce novelty in a population, nor the most common way. It is far more common to have recombination of previously existing mutations (genetic variation in a population) into new combinations. For humans and chimpanzees, for example, many of the differences we see between our two genomes were likely present as alternate alleles in our common ancestral population. These differences then sorted down to our two modern populations unequally - an effect known as incomplete lineage sorting.

Another thing to note is that single mutations do not, in general, produce large effects. Many mutations, combining and recombining over time in a population, can shift averages. When we compare the human and chimp genomes, for example, scattered small differences are the rule, not the exception. Yet these differences combine to give the differences we see.

I've written about these issues in more detail over on the BioLogos site (search under my name as an author search) and look for the "Understanding Evolution" series.

One last comment about your statement that "God-awareness" is either there or not there - what about our own development from infants to adults? Did we not become aware of God gradually through that process? Would not a similar progression be possible for our species over time?

Best,

Dennis

 There is a major aspect to your questions that I did not address in my earlier post. One assumptions you seem to be making is that their must be a physical (biological) component to being human in a theological sense (that is be able to be in communication with and image God). I believe that this in only the case in that there must be certain intellectual capabilities (self consciousness, empathy, awareness of past and present, creativity, logical reasoning, etc.) in place so that a creature has the potential to be in conscious fellowship with God. However, those mental capacities are not what make us God’s image bearers. It seems clear to me, that what defines our image bearing is relationships. That is we image God in that God has chosen to establish a relationship with us, and that relationship then extends out to other humans, and to the entire creation. The image is relational, not biological. It is not a consequence of our biology, but of God free grace in putting us in relationship.

Because of this understanding of being made in God’s image, I think that it is futile to try to discern the beginning of humanity in a theological sense from the fossil and anthropological record. I don’t see why there need be any biological difference at all between those individuals that God revealed himself to and made His image bearers. Becoming human was not a speciation event -- it was a divine act of grace.

I do not think that it is possible to define the beginning of the image of God through anthropology. It is also not a biological function that we can identify and that a person might lose through injury or genetic defect. We are images of God only because God is in special relationship to us.

All the best,

Keith

I said that humans must have certain physical capacities, that there is a minimum of intellectual abilities necessary for humanness. I agree with you that this is only a necessary and not a sufficient condition to have humanness. Any organism lacking these abilities and the genetic code needed to produce these mental abilities cannot be human unless God somehow miraculously intervenes to allow such abilities. Yet one who has these intellectual capacities is still not necessarily human. One may have the capacity to be aware of God and still not be aware of God should God not choose to allow one this awareness. This awareness need not be anything like what we might think of as a religious experience. It could be nothing more than the awareness that God could be there and that one has a moral obligation to this God should this God exist. This is more of a moral awareness though we might also call it a spiritual awareness.

So yes, it seems that God does have to specially act to give us our humanness, the image of God, and having all the right mental abilities is not enough. I could be wrong, but it does seem to me that this kind of moral awareness cannot result from mere physical capacities of the brain. I would certainly claim this of human consciousness (as well as animal sentience insofar as we can assume that animals do have sentience). J. P. Moreland, for example, develops an argument for God’s existence from human consciousness. No increase in complexity or in new arrangements of complex neural parts can produce consciousness in humans any more than making Star Trek’s android, Commander Data, more complex can actually give him consciousness. To claim otherwise is a category mistake. What I am questioning concerning moral awareness is whether, given human consciousness, this awareness can result naturally from some feature of human intelligence which in turn results from our complex brain structure. As I say, I don’t think it can.

You make the point that it would thus be very difficult to determine from studies in population genetic or archeology when the first humans came to be. But even if the characteristics I’ve suggested to be sufficient for humanness are genetically determined—that once we are physically made a certain way and behave and think accordingly, we must be human—it would still be just as difficult to say when the first human came on the scene. Might one in the line of common ancestors for the chimp and human line have been human? I claimed earlier that humans and non-human primates might have interbred until one line was left and the other became extinct or that both became distinct species. If all it takes to be human is a sense of God’s existence (or an awareness of the possibility of God’s existence), and an awareness of the obligation to relate to this God in a certain way (worship, obedience, etc.), and maybe a more general moral awareness also, then it seems very possible that the first human could be very early. I had mentioned the Upper Paleolithic Revolution as a likely starting point for humans because it seems that here the artifacts and other evidence indicate clearly modern human behavior whereas for any previous primates we can hardly tell the difference between their behavior and artifacts and that of any other higher animal. And I still think this is the more likely point at which humans appeared. But as I say, if we truly consider humanness to consist of moral and spiritual characteristics like those I’ve suggested, the first humans could have existed much earlier.

You have suggested some other characteristics such as creativity, logic, etc. which might put some rough limits as to when humanness could begin. But as you say, with this it is "futile to try to discern the beginning of humanity in a theological sense from the fossil and anthropological record.” I’m not sure if you are saying that to be human in a theological sense requires one to be in relationship with God. It should at least require the potential of relationship with God, that one may choose that relationship and God may allow it. But certainly those who refuse this relationship are (and were) no less human than those who choose it.  

You say, "I don’t see why there need be any biological difference at all between those individuals that God revealed himself to and made His image bearers. Becoming human was not a speciation event -- it was a divine act of grace.” Well, so long as they all have those minimal mental abilities and yet they still have that relationship with God (or, as I suggest, even the potential for that relationship), they certainly should all be considered human even though they be of different biological species. If there ever were more than one biological species of humans, then all must have become extinct except one.

 I will make only one comment.

 You stated: "But as you say, with this it is "futile to try to discern the beginning of humanity in a theological sense from the fossil and anthropological record.” I’m not sure if you are saying that to be human in a theological sense requires one to be in relationship with God. It should at least require the potential of relationship with God, that one may choose that relationship and God may allow it. But certainly those who refuse this relationship are (and were) no less human than those who choose it."

 Yes, I believe that being human (having the image of God) is based upon God's relationship to us.  We are human in the theological sense because God has graciously chosen to be in a special relationship with us.  However, that does NOT mean that it is dependent on our response.  We are God's image bearers regardless of whether we acknowledge or respond to that relationship or not.  That is why there is an historical redemptive story - God pursues those with whom He has established a relationship.

Our biology is NOT the basis of our humanity (except in the sense of possessing certain mental and social capabilities).  A creature capable of interacting with God could have as easily been evolved from the dinosaurs.  I think we place far to much emphasis on our biology in understanding our unique status before God and the rest of creation.

All the best,

 Keith