I am no expert on evolution. Not even close. But I have read an article of two on speciation and how that may occur. Fascinating reading.
One of the things that I gathered is that it is not necessarily the number of chromosomes that is important, it is the sequence of genes upon the chromosomes themselves that matters. Apparently you can have a chromosome split and still have viable offspring if the information sequence is maintained. You would just have lower fertility, but not infertility.
Apparently for complete speciation to happen you would have to eventually have two individuals with the split chromosome have offspring. AND then you would have to have further changes to assure that the new prospective species did in fact become a new species.
Kind of complex and way out of my specialty but interesting stuff. Apparently it is the sequencing of the genes on two of the ape genes that leads scientists to believe we have common ancestors. Anybody willing can google up chromome 2, 2A, and 2B for men and apes and get some fascinating reading.
