Others seem to like to pretend."
"I don't know" is the understood answer to many specific questions, but does not mean we know nothing about the subject, and what we do know may be worth rehearsing -- if only to restrict further arguments from ignorance.
ml/nj: "As for you splitting and/or combining chromosomes, we don't see any grandchildren of any animals with any chromosomial abnormalities, handwaving notwithstanding."
"Handwaving" describes your statement here.
Here's how one article addresses it:
- "Finally, some creationist-intelligent design writers have claimed that if such a fusion had occurred in an individual, that individual would not survive, or, at the least, would be completely infertile.
But researchers have long noted fused chromosomes in both animals and humans.
As Miller points out, a 2013 Chinese report described a 25-year-old male, otherwise completely healthy, with only 22 pairs of chromosomes instead of 23, the result of a fusion of chromosome pairs 14 and 15.
Similarly, a Spanish study described a case in which both parents of a family had by chance carried a fusion between chromosome pairs 13 and 14.
Three of their six children inherited the same fused chromosome pairs.
In short, none of these objections stand up to scrutiny.
Fusion happened, and humans and chimpanzees share a common biological ancestor."
- " The fusion of chromosome 2 did not present a significant barrier to reproduction.
The de novo mutation that produced chromosome 2 took place by means of a Robertson translocation.
Robertsonian translocation occasionally occur today in the human population, although they are seldom noticed.
The reason that they are unnoticed is because they don’t significantly affect the phenotype.
Robertsonian translocations don’t even produce a significant reproduction barrier.
One reason Robertsonian translocations don’t have a significant effect is that the Robertsonian translocation preserves the centromeres.
The chromosomes in the germline cell ‘recognize’ each other by their centromeres.
So as long as the centromeres are conserved, meiosis is no big deal...
"...Let me qualify what I just said though.
The Robertsonian translocation that caused the fusion of chromosome 2 probably caused an extremely small hybridization barrier that would be virtually unnoticeable in the first few generations after the de novo mutation.
The fusion of chromosome 2 would cause an extremely small hybridization barrier.
It would not be anywhere as big as the famous case of mules and hinnys.
Horses and donkeys have incompatible chromosomes due to a couple of de novo mutations that occurred a long time ago.
The apes with fused chromosome 2 would have been nearly as fertile as the apes without this mutation.
There would be a slight increase in the frequency of Down’s syndrome in crossings between apes with the fusion and without the fusion.
It would hardly be noticed in humans, let alone apes.
However, this small increase in risk could have caused a separation of ‘species’ over many, many generations.
People with a Robertsonian translocation crossing with people without the transplocation may have a slightly increased possibility of having offspring with trisomy 21.
Trisomy 21 causes Down’s syndrome, which in protohumans would have been fatal.
The increase in susceptibility is slight, but there probably is one."
How strong is the chromosome fusion idea?
Well, the first article above refers to it as the "fusion hypothesis", saying:
- "Creationists have also argued that there aren’t as many telomeres, or copies of the TTAGGG sequence, on either side of the fusion site as on the ends of most chromosomes.
But this too is actually consistent with the fusion hypothesis..."
- "Needless to say, Yunis’ and Prakash’s discovery largely confirmed the hopeful hypothesis that had been made decades earlier.
Nonetheless, conclusive, molecular-level evidence had to wait until the completion of the human genome project in 2003."
- "Some creationist-intelligent design writers, recognizing the strength of DNA evidence, have tried to mount arguments against it.
As Kenneth Miller notes in The Human Instinct, the Institute for Creation Research recently claimed that an active gene is located at the chromosome 2 fusion site, and therefore the whole chromosome 2 fusion theory is falsified."