Continuation of reply to Alec’s post 327. First part of my reply is post 408
Dear Alec,
Your readable format is sincerely appreciated. Thank you. My first objective was to read your evidence for understanding.
I did get hung up about the alleles for humans and the DRB1 gene and ended up giving my preference for clarifying. The whole bit of sharing groups of alleles with apes was fascinating. Finding the date for divergence was to me an exciting discovery. At that point, I put on my philosopher’s hat and shared some of my early perceptions about evolution. Just so you knew my limited background.
The rest of the presentation was more difficult. Though I did jot down questions, they don’t have to be answered because I think it is possible to do a simple summary. Did I use the word simple?
The second objective was to look for answers to some of my own curious questions. I found that the genomic make-up of human beings was well established. Evidence suggests that there was an origin that pre-dated the divergence of the chimp and human lineages. I’m assuming that this origin would be the common ancestor. I never figured there would be a bottleneck.
My third objective would be to describe the common ancestor. There were papers that looked like they contained descriptions. However, I will rely on your evaluation of them as to how complete the description is and on what it is based. I have my own imaginative description of the common ancestor in that it would have to contain the genomics of both sides of the split.
(Am I using genomics right?) plus it would have some genes which would be its own characteristics, give it its own existence. It does exist, doesn’t it? Then there has to be something which precipitates the split. Or is the common ancestor only two halves stuck together with Elmer’s glue? (Sorry, but I couldn’t resist that image.

)
The bottleneck in the rest of your presentation is a new idea for me. I jotted down a bunch of questions, but again I think they can be easily summarized.
hecd2:
Many of the DRB1 groups of alleles diverged many millions of years in the past, before the divergence of the human-chimpanzee lineages. Ayala (the same Ayala who is presenting a paper at the March conference at the Gregorian University) calculates that six million years ago at the time of the chimp-human divergence there were 21 lineages of allele which have survived to today, and that is not possible if humans have passed through a population bottleneck of just one couple.
Please note: I’m not after individual answers. Rather, I’m trying to picture what is happening. How would I draw it on a piece of paper? Maybe a time-line of stages? If there are stages?
I’m having trouble with the bottleneck concept and the divergence action. What basically is a bottleneck during human evolution?
Were there a lot of common ancestors carrying the exact combination of genes that would spontaneously divide into humans and chimps? Yet, there are studies which show that humans and other primates carry similar genes. Would there be a common ancestor for each of the human/primate combinations?
Regarding the bottleneck, here are some studies: Are they totally compatible with each other?
Apolipoprotein C II:
Xiong et al, ‘No severe bottleneck during human evolution; evidence from two apolipoprotein C II alleles’, Am J Hum Genet 48, 383 -389
Nuclear genome:
Rogers and Jorde, ‘Genetic evidence on the origin of modern humans’,
Hum Biol 67, 1 - 36, show that a modest bottleneck of 10,000 individuals is consistent with the data.
General studies:
Hawks et al, Population bottlenecks and Pleistocene human evolution, *Mol Bio Evol *17, 2 – 22 (2000)
Does the following study answer the question about the bottleneck stretching across continents?
Liu et al, A geographically explicit model of worldwide human settlement history,
Am J Hum Gen 79, 230 – 237 (2006)
Such a severe bottleneck would leave an unmistakeable signature on other parts of the genome too - other polymorphic sites in the autosomes (the non-sex chromosomes); on the Y-chromosome; in the mitochondrial DNA. All of these analyses agree that the minimum breeding human lineage bottleneck in the last six million was 10,000 individuals and that a bottleneck of two people in the last 200,000 years is just not tenable.
Is this 10,000 individuals describing the idea of --the word is somewhere in someone’s post – humans descending from a bunch of common ancestors?
My fourth objective would be my impression. I don’t have one yet.
Blessings,
granny
All human beings are fascinating.