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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?
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/
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."
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."
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.