I posed this question to dwise in the thread "Creation vs Evolution is a 'Red Herring' argument" (I don't know what the thread ID is or I would have included the link) and never received a response. Since I am curious about the answer to this (and it was a bit off topic over there), I am proposing it as new topic.
Message 68
So just what the frak is this imaginary barrier that you're fretting about?
I suppose the barrier that PaulGL is referring to (although he doesn't appear to know what he is referring to) is the fusion of human chromosome 2. This event could bring about the "hopeful monster" you referred to in
Message 62. It is a sudden, major genomic change and contrary to
Message 62:
quote:
Rather, the degree to which each generation of a changing population changes is very slight; "sudden" changes in the fossil record (in geologic time, so in thousands of years) result from the accumulation of lots of small gradual changes with each generation (in generational time, so in one to a couple tens of years, depending on the species in question).
This fusion did not occur a little bit at a time, in small gradual changes. It may have made a small difference morphologically, but it was a major event in the genome.
Now whether this fusion event itself caused infertility or not is uncertain. In at least in one situation, the Przewalski's horse (mentioned by Coragyps in
Message 61), this type of event does not cause infertility but it does result in offspring with a conglomerate of chromosomes ie. 65 as opposed to 64 or 66.
Since none of the great apes are known to have 46 chromosomes, it is most likely that either:
1. The fusion event caused the split OR ...
2. The fusion event occurred within the human lineage (after the chimp / human split)
If option 1 is true then either
1. The fusion caused infertility in which case we have the dilemma that PaulGL supposes OR ...
2. The fusion did not result in infertility in which case we should have a Homo spp. (living or extinct) with a conglomerate of chromosomes, such as with Przewalski's horse.
If option 2 is true then
We should see Homo spp. (living or extinct) with 48 chromosomes, Homo spp. (living or extinct) with 46 chromosomes AND Homo spp. (living or extinct) with chromosome conglomerates, ie. 47.
Is there any evidence that Homo spp. have chromosome numbers other than 46? Note: I do understand that we don't have access to all DNA from all extinct species and that absence of evidence is not evidence of absence.
You assumed that that event had to have happened within a single generation.
Since chromosome fusion is a relatively rare event, I would assume that this event did occur in a single individual and then spread to that individual's descendants. And since all known hominids except humans (Homo spp.) have 48* chromosomes, it seems most plausible that option 1 is true (that is: the fusion event caused the split). And since it is pretty obvious that the human lineage survived (the event did not cause infertility), shouldn't we expect to find Homo spp. (living or extinct) with a conglomerate of chromosomes?
What is the most accepted understanding of this? Are there any known hybrids of species with different chromosome numbers that do not have a conglomerate of chromosomes?
*edited 24 chromosomes to 48 so that all references were to diploid numbers
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for. But until the end of the present exile has come and terminated this our imperfection by which "we know in part," I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
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