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original human population size
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7/8/2012 at 9:21:59 PM GMT
Posts: 12
original human population size
I’m new on the forum page and, not being a scientist, I’ve recently joined ASA as a follower. Because I generally lack contact with specialists in the sciences, my hope is that this forum page will be a means of answering some questions that have been bothering me.

My question at the moment involves the current evidence that there was no original first human couple but rather a population of several thousand at least. The Sept 2010 issue of PSCF covered this and related topics such as the increasing evidence for common descent. Still, I’m not sure I even understand the meaning of this claim concerning the number of the first humans.

If in the following description I’m entirely off base, please correct my misunderstanding.

My understanding of the orthodox Darwinian view is that for evolution to occur an individual has a genetic mutation that happens to be beneficial in the sense that it bestows some survival advantage in the particular environment one finds oneself. Assuming some mutation brought about the first modern human (hereafter, human), this mutation would have to occur for one individual. Technically, one individual would produce the mutation, mate with another non-human primate who lacks the mutation, and potentially produce an heterozygous offspring. Suppose the offspring were a male, call him M2-1. (M2-1 would mean, M: male, 2: second generation, and −1: heterozygous; −2 would indicate homozygous, −0 would indicate no mutation for the given gene.) M2-1 would mate with F2-0 and one or more of their offspring could maintain the heterozygous mutation. Or M2-1 could mate with a sibling who happens to have the mutation, F2-1, and possibly produce one or more homozygous, heterozygous, or non-mutated offspring. The selective advantage of this mutation will gradually increase these humanly mutated individuals in the breeding population.

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.



7/8/2012 at 9:48:52 PM GMT
Posts: 130

Dennis,

  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



7/10/2012 at 7:46:40 PM GMT
Posts: 6
Good approach to this question Randy

I would agree with Randy that it is important to consider that in a given population there is always variation, and not just single gene changes that lead to this variation. Two siblings differ at a number of genes, not just one. Between any two species there are many diferences, and speciation can result from a number of different mechanisms. Two parents having a new species offspring is generally not one, at least for large complex organisms. A great example of speciation occurring among salamanders in California illustrates the point. You see that the parent species is at one end of the state, whereas the newly forming species are on either side of the desert.  Over time, there will be three species where there was originally one.  Now, you can see how it is not correct to ask who the original two parents of the new species were.    Here is the link to that video. http://www.youtube.com/watch?v=YCoEiLOV8jc   Of course, many will say "that's microevolution, not macroevolution." Interestingly, most biologists don't find the term microevolution all that useful. This distinction really misses the point: These are the mechanisms that logically will inevitably lead to changes in species, and if the fossil record and genomic evidence is to be believed, it is reasonable to infer that these smaller changes do accumulate to bring about remarkable changes. 

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



7/10/2012 at 9:13:00 PM GMT
Posts: 12
Thank you for your reply, Randy, that does help a lot. I’ll be interested in seeing other replies as well. I see another reply has come through but it will be a little while before I can respond.


7/11/2012 at 8:49:38 PM GMT
Posts: 12
encourage specialists to respond

Randy. I know you are the current Executive Director of the ASA and I appreciate your taking the time to respond to some of these forum discussions when you could probably have a much greater impact speaking or writing in more widely viewed publications. I think you recognize that there is an important ministry simply in speaking to sometimes even just a single individual. There are people like myself who simply need to discuss our questions with a specialist. Could I suggest that, whenever you have opportunity, encourage other specialists to watch the ASA forums, at least check out the topics that are being covered, so that they too might be able to use their expertise to give needed information to nonspecialists like myself? I think they too could find this to be a very important ministry.

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




7/12/2012 at 1:14:49 AM GMT
Posts: 12
Thank you for your reply, Randy. I know I introduced myself as someone who, as a non-scientist, is just looking for clarification and understanding. Forgive me for my almost Jekyll and Hyde change in demeanor but I’m going to have to strongly dispute some of your statements.

Having read Dennis Venema’s Sept 2010 PSCF article I do think the evidence for common descent is now much stronger than it has been in the past and that we do have to accept that human evolution occurred within relatively large populations (that is, a bottleneck of maybe 10,000 interbreeding individuals as compared to two). I’ve accepted the arguments for common descent for many years and have no problem there. It is your claim that speciation occurs gradually and that it cannot be discussed in terms of individuals that I question. Just because population genetics works this way does not mean that we cannot look at individuals and discuss the issue in terms of individuals.

Wasn’t one of the reasons the punctuated equilibrium model was developed was because of the problems of the apparent suddenness of appearance of new organisms in the geological record? Michael Denton in his critique of evolution some years ago (Evolution, A Theory in Crises) pointed out that there are grave problems with some of the changes from one organism to another as we get higher on the scale of taxonomic categories. The change from the reptile to bird lung, for example, looks like something requiring multiple, simultaneous, beneficial, genetic mutations. I haven’t kept up on the discussions to know whether this claim has ever been adequately answered but it seems that there is a least a problem for the gradualists.

You say, "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.” But if the genome of each zebra, dog, cat, human, etc. defines that species, genus, etc. (the parameters of variation for each genome, if that is the proper term here, increasing as we reach higher categories) then it seems that, necessarily, the first organism to possess that particular genome was the first of its kind. If we have a genetic change, a mutation that finally makes a new species or even subspecies, then it is a new species or subspecies and there is a true first one of a kind.

It shouldn’t be difficult to imagine that a new species or subspecies may begin with a final mutation after a number of others. The previous mutations may not produce much change or even any change but with the final mutation the organism becomes very different from its parents. Surely the idea of one significant mutation (as I say, maybe a final mutation) producing a beneficial change and bestowing an advantage greater than that possessed by the rest of the population, is a feasible means of evolutionary change. Wouldn’t this be even more likely in a population of 6,000 to 10,000? So we have here a means of gradually diminishing and eliminating the previous (non-human) population while at the same time increasing the human population. But it also follows that the mutation has produced an individual of a new subspecies and the subspecies can be significantly different from the parent subspecies.

For the sake of the argument, let’s assume that your very gradualistic description is accurate for all evolutionary change (other than by asexual reproduction). We still have no good reason to think that this must be the case for humans. The genetic difference between ourselves and our last primate ancestor, whether great or small, is significant enough to make us very different from that ancestor. With the Upper Paleolithic Revolution, it appears that humans had become something quite different than their predecessors.

Now if it is simply illegitimate for scientists to think of there being a first human, then if nothing else, we should see that at least God would recognize when the first human came into being, that God would know that one primate is not human and another is. It seems more likely that God would deal with that individual (or couple) rather than with some other representative human or human couple of a larger population of humans. But there are difficulties with this representative view. For example, it would require the representative humans exist later than the original, first human individual or couple. We have a problem with a representative couple acting retroactively for previous individuals. If Genesis present Adam as a metaphor for humanity, we have other problems. Does all of humanity simultaneously choose to disobey God? John Schneider’s supralapsarian approach (again in the Sept 2010 PSCF) could certainly assume such a thing but it falls prey to the same problems we find in similar Calvinistic or other deterministic theologies. It holds people responsible for acts they cannot help but commit and thus it makes God unjust. So if at least God can identify and deal with a first human couple, this is more likely what the Genesis account records.

With this, I think we can keep the Genesis account as an accurate description of spiritual truths. Being poetic literature it should be read poetically. With our newer genetic information we have a better grasp of what actually happened though this information certainly does not contradict the Genesis account. Maybe after you critique this blog I will say a little more about how I now see the Genesis account, what it teaches, and how it relates to the actual historical events. I’d be interested in seeing your critique of this as well.


7/12/2012 at 2:40:15 PM GMT
Posts: 6
Species concept

One thing you are getting into, DJ, is the very challenging topic of "What is a Species?"  or "Species Concept" and just a caution (from a biologist) that this is itself a very challenging topic within the field of biology. Suffice to say there are many ways to define what a species is. Of course Wikipedia can give you a good treatment of the topic. There are over 10 different ways listed there to define a species: http://en.wikipedia.org/wiki/Species   Good luck!  

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



7/12/2012 at 9:21:08 PM GMT
Posts: 6
Speciation
I also want to welcome you to the ASA and the ASA forum.  My name is Keith Miller and I am a long-time member of the ASA.

I will try top respond to your inquiry as well as I can in a brief post.  I am not an evolutionary biologist or geneticist, but a paleontologist.  So I come to such questions from the perspective of the fossil record.

As stated by Randy, evolution and speciation is a population phenomena, not one of individuals.  That is because the genome of a species is a population genome that includes all of the genetic diversity within that interbreeding population.  The genetics of those populations, and the anatomical characteristics that are expressions of the genetics, change within those populations.  The biological species definition is a population definition -- "a population of interbreeding individuals that are reproductively isolated from other similar populations under natural conditions.”


The recognition of modern species is not a straightforward process.  There are populations of organisms that form a continuum of conditions from completely genetically isolated, to species populations with limited but non-zero genetic interchange, to subspecies that may interbreed when they come into contact (and form hybrids), to ring species that vary across their geographic range populations but cannot interbreed where the two terminal populations come into contact.  The difficulty in identifying living species is significant -- usually species are simply identified by a set of diagnostic anatomical characters and not according to the formal biological species definition.  

When defining species from the fossil record, the biological species definition obviously cannot be applied, and all that is left is the suite of observable anatomical features (and an incomplete set at that).  Fossil species are usually described as a population of specimens with a certain range of variation around some mean of specific character states.  The observed variation within the defined species population should be less than the difference between those traits and those of other defined species populations.   If later discoveries show that the defining characters significantly overlap between two defined species, then those species become "synonyms.”  Species always imply a certain degree of morphologic variation.  Now because of the limits of the fossil record, we may only have a few specimens that have been designated as a distinct species.  This happens if they are distinctive enough from all other known previously known specimens.  But what may, and often does happen, is that when more new fossils are discovered those species definitions are abandoned or redefined. In a very real sense the vagaries of preservation on the fossil record determine our species definitions because the samples are discontinuous in time and space.

"Punctuated equilibrium” has generally been very misunderstood by the lay public (and even some in the scientific community).  It was not intended to imply discontinuity at the level of evolving populations, but rather it was applying the concept of allopatric speciation to the fossil record.  Allopatric speciation argues that the most common mechanism for speciation is the isolation of a small population due to some physical, climatic, or other barrier to gene flow.  The resulting genetic isolation (or very reduced gene flow) allows the small population to evolve at a higher rate because it has less genetic inertia.  Because the more rapidly evolving isolated population is very small, and occupies a small geographic area, it will have little or no chance of actually being preserved in the fossil record.  Only once the species population has expanded both in size and geographic extent will it have some change of being recorded in the fossil record.  However, population genetics suggests that rapid evolution within large populations in difficult -- unless there is some long-term environmental change that forces adaptation.  Thus the fossil record would most commonly record large slowly-evolving species populations, and fossil records of the speciation process itself would be rare. Evolutionary rates are thus variable over time (they are punctuated), and the fossil record is not likely to capture those changes occurring during speciation itself.  There are examples in the fossil record, but they are rare.

Finally, it is very important to recognize that named taxa above the species level are abstractions.  They are the result of the application of particular rules for classification and grouping of species.  Higher taxonomic categories (genus, family, order, class, etc.)are also highly fluid and change as the body of fossil data increases and as taxonomic procedures change. The appearance of a new higher taxon in the fossil record is simply a speciation event -- no more, and no less.  There is nothing especially dramatic involved. In fact, two species placed in different higher taxonomic groups may be, and often are, virtually indistinguishable.  I discuss this in my chapter - "Common descent, transitional forms, and the fossil record” - in my edited volume "Perspectives on an Evolving Creation.”

All the best,

Keith



7/12/2012 at 10:29:38 PM GMT
Posts: 12
Craig, thank you for your comments. I’m not sure that the definition of a species is the important thing. The idea of any class of all organisms that can interbreed is good enough for our purposes. The first humans would have actually been a subspecies given this definition if they could have interbred with their parent population of non-humans. The important issue would be whether the two, even if they were both mere subspecies of the same species, were sufficiently different that one could relate to God and the other could not. At least we do not know if animals relate to God; if they do, it is in some way we do not understand. The following are some comments I had made before seeing your new response.

Looking at the salamander example you raise, wouldn’t the two new subspecies (not species yet since it appears that they can interbreed) each have essentially a limited form of the genome that is found in the parent population? Where then is there any substantial evolutionary change? Isn’t it when an individual has a beneficial mutation that a real change in an offspring (and then its breeding population) occurs? Might the color variations in the salamanders, while beneficial for survival, have resulted from mere genetic variation in the species? How then can this be called evolution? And even if we do have true speciation occurring (suppose the bright red salamander in the video represents a new species) then we still had a first salamander with the genome that defined that species. 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.


7/12/2012 at 11:49:33 PM GMT
Posts: 12
The Genesis account given the new genetic studies.

Before responding to Keith Miller's new comments, I wanted to throw out a possible scenario regarding how we should see the Genesis account given the newer genetic and other scientific information we now have. So far, my only disagreement with some of my other correspondents is that it seems to me undeniable that there was a first human couple and this couple was most likely the biblical Adam and Eve.

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.



Last edited Friday, July 13, 2012